400 Biochemistry MCQ's PDF

Self-evaluation guide for medical students 400 Biochemistry MCQ's Professor Maria R. Sanchez A guide to self-evaluation 400 Biochemistry MCQ's Professor Maria R. Sanchez 400 Biochemistry MCQ's by María R. Sánchez is distributed under a Creative Commons Attribution License- NonCommercial 4.0 International Caracas, 2018 Table of contents Foreword....................................................................................................... 6 Section One....................................................................................................... 7 Reflections on undergraduate Biochemistry........................................7 Teaching, learning and evaluation..........................................................7 The illusion of understanding.............................................................8 Suggestions...........................................................................................10 The teacher’s side................................................................................10 The student’s side................................................................................15 Section Two..................................................................................................... 20 Reflections on evaluating biochemical knowledge...........................20 Evaluation as a tool to achieve objectives......................................21 Section Three.................................................................................................. 26 Multiple choice questions.......................................................................26 On Structure of amino acids and proteins....................................27 On Enzymes......................................................................................... 32 On Cell Biology....................................................................................41 On Membranes...................................................................................58 On Introduction to Metabolism and Signal Transduction..........63 On Krebs cycle and oxidative phosphorylation............................68 Metabolism of Carbohydrates..........................................................81 Metabolism of Lipids..........................................................................94 Metabolism of Amino acids.............................................................106 Hemoproteins and Nucleotide Metabolism..................................111 Nucleotide Metabolism.....................................................................117 Metabolic Integration and Regulation...........................................119 Nutrition and Digestion....................................................................138 Alcoholism........................................................................................... 147 Cutaneous Porphyria in alcoholic patient....................................149 Obesity.................................................................................................. 151 Metabolic Syndrome.........................................................................154 Hypercholesterolemia and overweight........................................155 Hypercholesterolemia IIa.................................................................156 Myocardial infarction........................................................................158 Type 1 Diabetes..................................................................................160 Type 2 Diabetes................................................................................. 162 Iron deficiency anemia.....................................................................165 Anemia associated to infectious processes.................................166 Sickle Cell Anemia.............................................................................167 Glucose 6–P dehydrogenase deficiency.......................................168 Hyaline Membrane............................................................................169 Gilbert’s Syndrome............................................................................170 Biochemistry is also useful in understanding other kinds of medical problems...............................................................................171 References................................................................................................ 175 Foreword This book is intended to be a tool for medical students and their teachers. It is inspired fundamentally by my experience of over thirty years dedicated to teaching Biochemistry at the Razetti School of Medicine (Escuela de Medicina Luis Razetti. Facultad de Medicina. Universidad Central de Venezuela). The student readers will find in it a set of recommendations I hope will be useful for their approach to the study of Biochemistry. There is also a second part with a large series of questions designed for self-evaluation. In that part, younger teachers will find some guidelines for the making of questions, something that may lighten the burden this task poses to them. The book is based on my experience as a teacher, something that over the years has been food for reflection, study and research on the obstacles that hinder student performance. I hope this work will suggest ways for teachers to help students to overcome such obstacles and students to practice self-help on this pressing matter. (1,2,3,4,5). Section One Reflections on undergraduate Biochemistry Teaching, learning and evaluation The illusion of understanding It is a common experience to find that some students do not understand why they get low marks when evaluated on a subject they have the illusory feeling they understand fully and on which they have worked hard. We, teachers, have often met students overwhelmed by that sad situation, something that drives us to feel there is, unfortunately, very little we can do to get them out of error. It is indeed a hard problem and a difficult one to solve; in my view, for students this problem represents a very difficult hurdle and for teachers an even greater challenge than guiding them to grasp and comprehend a difficult concept that they consciously acknowledge not to follow. The causes of this illusion are varied. Some of them have been identified by experts on the subject and lie in a bewildering wide range of factors that span from ‘misconceptions’ to the effect of internet on that illusion, the latter instance clearly shown by recent studies on the theme (6,7,8). It is not my intention to address that subject here. However, experience has allowed me to identify some frequent sources of error that can be treated here, albeit superficially. One of them is the tendency frequently shown by students to satisfy themselves with teleological or functional explanations of what they are studying; this may lead them to believe this is what is expected not realizing that they have to demonstrate their knowledge of the biochemical events involved. An example: To the question ‘Why does the synthesis of ketone bodies increase when fasting?’ The answer is ‘Because there is need to save glucose in order to ensure the function of tissues that need it’ or something of that sort; this answer plainly disregards a series of hormonal and metabolic changes that result in ketone body synthesis. In my opinion, this tendency to try explaining phenomena functionally or by teleology is a reasonable and natural mental process. Such a course of thought may even help us when doing research work in reasoning and understanding (I am sure many scientists will agree on this point). But, and this is a big but, in the student´s case it may actually be an obstacle to learning biochemical phenomena. In the example above, we can help overcome this type of obstacle if, while acquiescing to the ‘functional’ explanation, at the same time point out that cells (let alone molecules) do not ‘think’, and for that reason cannot know there is ‘need to save glucose’; i.e. that there is an essential difference between a series of chemical events and a series of mental events. It is also common among students the noxious idea that transforms biochemical reactions into something akin to alchemy. In this line of thinking molecules change ‘magically’; it goes something like this: ‘oxaloacetate becomes malate’ or ‘glucose becomes glucose 6-phosphate’, and so on. The enzyme concerned is missing! In statements like those just mentioned, there is not a clear notion that when a substrate changes into product a chemical reaction has taken place. This image of a ‘magical transformation’ is probably the reason why students forget to mention the role of enzymes catalyzing intracellular biochemical processes, an all- important point in the biochemical learning process, since regulation of metabolic pathways depends on activation/deactivation of certain enzymes. And that is a key concept to understand and explain metabolic changes happening in the body as an effect of the action of hormones or neurotransmitters. Suggestions The teacher’s side Ways to help Part of the erroneous conceptions many students show may be due to an inability to construct an adequate mental representation of phenomena. In their view, Biochemistry, in contrast to Anatomy or Histology, is an abstract and alien subject and abstraction is not easy at this stage. This inability may have its origin in the way teachers and many textbooks approach some matters. For example, the naïve impression that a cell is a sort of big swimming pool where organelles and molecules move freely; thus we hear statements like “Glut 4 transporter ‘translocates’ from cytoplasm to membrane” that may actually impair a correct interpretation of this phenomenon. In this example, in order to facilitate a mental image of what the students are trying to learn and consequently its comprehension, it would be advisable to mention the role of the cytoskeleton, membrane adhesion molecules, membrane interconnection, etc. in order to facilitate a mental image of what the students are trying to learn and consequently its comprehension This mention to structure need not be detailed or extensive; a brief mention will suffice in most cases. Another important point is that too often we, the teachers, fail to mention what to us but not for the student, is obvious; this simple lapse in explaining may be the reason for a lack of understanding a biochemical process. An outstanding example of this is found when biochemical knowledge is presented like alchemy and the need for molecular contact is not explained, when it should be stressed that ‘molecules must come into contact’ for a chemical change to happen; e.g. typically, transference of cholesterol and apoprotein between two lipoproteins is described in a majority of textbooks with expressions like ‘HDL transfers…’ etc. When explaining, we fail to emphasize the fact that for a chemical reaction to take place there must be a physical interaction between reactants. There must be an efficient interaction between molecules for a transformation to happen. It may seem obvious to us, but if it is not given due emphasis, for some students the result may be their inability to relate adequately a concatenated series of events. They do not grasp the idea that this contact is necessary and we do not realize we are using a biochemical language familiar to us but not to them. As Miguel de Unamuno (Spanish philosopher, 1864- 1936) used to say ‘There is great need daily to repeat what, being so well known, is forgotten’ 1 The way students approach studying Medical students are for the most part studious and disciplined; from this statement it follows that if they have problems with academic performance in Biochemistry, it is seldom due to lack of work; their problems are far more likely to arise from an inadequate way of tackling the subject matter. A superlative example is the use of flash cards. This may induce the person that makes them to feel they know their contents, when probably all it does, at most, is ring a bell. Some students spend much time making impeccable cards or summaries, something that probably soothes their anguish because they get the impression that all contents is organized. It is sad to think that in fact they have wasted precious time that would have been better used in trying to understand what they are writing down in the card. Wrongly, they feel that summaries are abbreviated copies of the program’s contents instead of what they should be: a brief of what they have comprehended and understood. Alas! Making summaries makes sense when it is a personal synthesis of what has been learned. In my university there exists the figure of Advisory Teacher: students attaining poor results are assigned to a lecturer for guidance. As part of my work I played that role for many years. I always started by asking students to show me their notes, summaries and any other relevant material of study they made and used for studying. In many cases there were beautifully color-illustrated copybooks and to my surprise, some of them had been handed down by students that had previously passed the Biochemistry course. They were baffled when told ‘Throw away the lot, for it is of no use to you’. Surprisingly (or not?) very few took my advice! Another fact of relatively new occurrence is the use of internet. It may goad the student into the belief that this information in the web is akin to having it ‘inside their head’ (8). Although not intending to reinforce memorization, I firmly believe it is indispensable to memorize some ideas and facts. In teaching, it is generally taken as pejorative dogma that to memorize is sinful. Nevertheless, it is virtually impossible, for example, to deduct what happens in metabolism when there is lack of insulin if a few facts are not taken into account. And evidently those facts are used in the deducting process because they are in our memory. What is certainly inconvenient is to memorize mere facts and/or useless (or nearly so) knowledge. For instance, it is of little use, if any, to memorize all the reactions of glycolysis if there is no comprehension of glycolytic activity within the frame of particular metabolism of the diverse tissues. and the functioning of the organism as a whole. In ultimate terms, this is what really matters from a physiological point of view. The importance of insisting on the regulation of enzyme activity in the various metabolic pathways and the complex interactions among them cannot be overestimated. Teachers have a significant role here in the guidance of the student on what should be memorized and what should not. 2 The importance of Biochemistry in medical studies Most medical schools feel the need to stress the important relationship between Biochemistry (and other so-called ‘basic sciences’) and sound medical practice. This has brought the incidence of new ways of teaching, the restructuring of programs and the use of vignettes referring to clinical conditions. I contend that it is not good practice to obviate some biochemical knowledge just because it cannot be evidently related to disease and clinical practice. In my view some instances of basic biochemical knowledge are necessary to understand medical publications or certain clinical conditions. For example, the enzymic concept of the constant K M is an essential one to understand the activity of enzymes dealing with glucose in hepatocytes. There is another pitfall on this subject, which is to make a forced relationship with a clinical subject, something that may easily upend Biochemistry teachers. An outstanding example: using a case of acute porphyria to highlight the importance of biochemical knowledge. Normally, a case is presented of a patient that comes to hospital with abdominal pain of unknown etiology, a typically challenging case for doctors. But then biochemists make up questions about biochemical aspects of porphyria that have nothing to do with the pain that brought the patient to hospital or the biochemical changes that contribute to this pain appearing… simply because, to this day, nobody knows for certain the reason for such pain! This is a clear [wrong] message to students: the relationship of Biochemistry and clinical studies is something esoteric. Would it not be better to use a case of hematopoietic porphyria? This disease, besides being more frequent, does allow relating the effect of sunlight on molecules with the patient’s symptoms. And also, using it as model would allow the connection to the use of δ aminolevulinic acid in phototherapy. This porphyria may be less interesting from the intellectual clinical point of view, but it shows a clear link between biochemical knowledge and understanding disease from the scientific angle. Yes, it is an agreed dogma that a scientific training is an obvious necessity for a good doctor. On the other hand, it is of the utmost importance to realize that the practice of Medicine is a complex endeavor: without the ability to communicate with patients and an understanding of their individuality, clinical Medicine loses a sizeable part of its sense and efficacy. This poses a dilemma: arguably, scientific knowledge is not the most important part of the skills a medical student must acquire. And, yes again, at the other end of the spectrum is the emphasis on irrelevant biochemical detail for the comprehension of molecular basis of disease. An amalgam of these two factors, the individuality of patients and irrelevant detail might make the student believe that there is no need for Biochemical knowledge to be a doctor. Following this line of argument, let us think about the idea of highlighting the relationship between Biochemistry and Medicine by means of the use of rare diseases as examples. This may be very illustrative of the importance of a particular enzyme, like the deficiency of muscle glycogen phosphorylase (McArdle’s disease). This may be very interesting for biochemists, but for medical students it might suggest that Biochemistry is related only to strange diseases of little frequency. If this type of example is to be used, there must be caution and emphasis in that these diseases are examples and the students are unlikely to see a case of any of them in their whole life. Actually, there are frequent pathologies, like diabetes, obesity, hyperlipidemias, iron deficiency anemia, liver diseases and cancer among others, that offer good opportunities to illustrate the important relationship of Biochemistry and Medicine. I do not apologize for my insistence on this point, it is wholly intentional. Furthermore, making the case for Biochemistry in Medicine and in parallel with the above warning, there is no doubt that biochemical knowledge is essential to confront some misleading offers of drug advertising, a tendency that in present day world is no small matter. Nowadays and with increasing frequency, a doctor who has the discipline or the need or just plain and simple curiosity of reading scientific articles, faces (in any field) a very strange language, fit for experts, full of terms and abbreviations that seem to make up a secret code. In this area teachers of Biochemistry have a task as important as linking Biochemistry and Medicine: capacitate the student for self-learning, for continuous education. This has become a very important matter and, in fact, it is a problem that tends to get more complicated with time. The student’s side Suggestions for students: How to study. The following recommendations are complementary to those on hygiene of study habits (not dealt with here) and are specific for studying Biochemistry. Question the book. Do not read it as a novel. Work on the concepts, and since it is known that attention to study diminishes after about 45 minutes, it is advisable to take a small break after this lapse of work. This also means that if you spent that time reading generalities you will have ‘wasted’ time reading not-very-important issues. It is indeed surprising how little students use the analytical index to look for what they want to know. Try to get familiar with its use, it will save a lot of time. Try to make a study plan encompassing all you want to revise. Try to be specific on what you want to know, which requires assessing with precision what you know or think you know. Previous evaluations, if accessible, may be very useful for this. I consider it excellent habit that teachers foster analysis of student´s mistakes in evaluations. Don´t be afraid of chemical formulae: they may be useful to understand processes. Searching through Internet I recommend finding and using criteria of confidence for information found in Internet. There are quite a few universities’ pages on the subject. Here I mention some of them: http://guides.lib.berkeley.edu/evaluating-resources http://www.library.georgetown.edu/tutorials/research- guides/evaluating-internet-content It is also recommended learning to make your search more efficient: http://www.ed.ac.uk/information-services/library-museum- gallery/finding-resources/library-databases/databases-overview/ databases-search http://libraryguides.mta.ca/research_help/research_tips/ academic_research While it is important to become an expert searcher it may be harmful to become a compulsive searcher. Keep in mind that finding relevant and trustworthy information does not mean it is understood. In just the same way it is unnecessary to read three (or many) textbooks to learn the basics, it is unnecessary to spend hours searching internet for something you can easily find in a textbook. Actually, the internet features that may be of great help in understanding and gaining insight and knowledge are animations and simulations. Here again, it is vital to make sure the source is valid. Now, a few helpful tips that may be used to study metabolism. Bear in mind that an immense majority of biochemical transformations are catalyzed by enzymes and that they will not happen at any detectable speed in the absence of a specific enzyme; this is a basic reason why every time you refer to a biochemical transformation, the enzyme involved in catalysis must be mentioned. Draw a scheme on a sheet of paper for every metabolic pathway, especially pointing: Tissue where it takes place and subcellular location Irreversible reactions Reactions where ATP is formed or spent (Also GTP) Reactions where oxidation-reduction coenzymes are at work (NAD, NADP, FAD) Reactions where branching of a metabolic pathway occurs or where there is connection to another pathway. Regulatory enzymes. Keep these sheets handy all the time you are studying, for you will have to refer to them constantly for specific reactions. Don’t try to memorize them at the first approach. As you analyze each metabolic pathway, its regulation and relationships to other pathways, you will memorize them effortlessly, if that should turn out to be necessary. You must make it clear in your mind whether an enzyme is a regulatory one, and if so: To what kind of regulation is it subject? Does a hormone trigger its activation of inhibition (‘signal transduction’)? Identify the enzymes that interconnect pathways that happen + simultaneously. For example, reactions that use NADH + H from beta oxidation of fatty acids for gluconeogenesis. Identify biochemical facts that allow these interactions. Keep in mind that neither molecules nor cells ‘think’ and therefore a biochemical transformation only happens if the enzymes involved are not only present but in thei0r active form, besides other necessary chemical conditions. Separate pathways according to the physiological situation in which they occur. Enumerate those in fasting condition (glucagon and adrenalin prevalence) and those in post absorptive state (insulin is prevalent) Identify in each physiological situation which ways are oxidative or catabolic and which anabolic. Notice that in each physiological situation oxidative ways provide the reducing power and energy for the synthetic ways happening simultaneously. Identify hormonal changes that bring about changes in each situation as well as the way in which hormones influence enzymatic activity: Receptors, G proteins, transcription factors Production of ‘second messengers’. (Which?) Activation and or inhibition of enzymes (Which?), via what mechanism? Allosteric? Covalent modification? Regulation of gene expression Following these guidelines may help you to understand better what you read and minimize the need for memorizing facts. As for the themes dealing with storage and transmission of genetic information, once again: Enzymes, enzymes, enzymes. Particular features of each one of those processes depend on enzyme characteristics. For example, the impossibility of DNA polymerase to initiate synthesis starting from two mononucleotides explains the need for a primer. Make sure you understand what 5’ and 3’ mean. Keep in mind that all relationships among nucleic acids are given by complementarity anti parallelism. It may be obvious for many, but even as generally explained: first replication and then transcription and translation, only the latter two are sequential. At which point in cell life do replication, transcription and translation occur? How are they regulated? If you understand the basics, you will find little trouble in understanding the rest of it. Section Two Reflections on evaluating biochemical knowledge Evaluation as a tool to achieve objectives Any conception teachers have on the role of Biochemistry in medical studies will be inevitably found in the way they evaluate students, something that to my mind would lead to the desirable practice of self-questioning on this subject. In spite of the teacher insisting on the importance of a certain point, or the emphasis on that point made in the textbook, the student will not realize his understanding (or lack of ) until the point turns up in evaluation. And this is one of the functions of evaluation, be it formative or additive: to make the student conscious of what has been understood and what has not. But this is a valid point only if evaluation is rightly done. The way we plan and deploy evaluation can contribute to overcoming obstacles to understanding…or foster them! For example, if when evaluating we insist on molecular details of little relevance for a clear understanding of the theme, then students will focus their attention on those details when studying. We humans have a knack for interpreting signals that point to what is expected from us. The teacher must ask himself what he/she wants the students to learn. Sometimes it is good practice to write the answer we would like to receive before writing the question to which ‘that’ is the answer. When we assemble multiple selection questions, we frequently think of erroneous (false answer) items because we remember mistakes made by students. A good question can be a stimulus to curiosity or direct attention to aspects not taken into the picture previously. The importance that questions considered easy may attain cannot be underestimated: they may be clarifying and integrating, thus becoming organizers of thought. If the main interest is to underline relationships between tissues, processes and/or metabolic pathways, some questions may be very easy. For example: Apo B48 and Apo B100 have in common: a) The kind of lipoprotein that transports them b) The receptor to which they attach c) The gene that codifies for them d) Being freely transferable between lipoproteins e) The tissue where they are synthesized Just intends to bring attention to RNA processing and lipoprotein metabolism. Multiple choice questions There is much bibliography pointing to features a good multiple-choice question should have. I especially recommend: Item Writing Manual from National Board of Medical Examiners (NBME) http://www.nbme.org/publications/item-writing-manual.html - Test Construction: Some Practical Ideas for Marilla D. Svinicki, available in: http://www.rubrics4assessment.net/test_construction.pdf Presently I include a summary: 1. The leading statement must be meaningful itself. It may or may not be a question. One word statements are not recommended 2. It should not contain non-pertinent material 3. As far as possible, avoid negative statements. Like ‘The following are NOT properties…’ 4. All items must be grammatically congruent with the leading statement 5. There must be only one correct answer. Avoid the use of ‘the most correct…’ or ‘the best explanation…’ 6. Item length should not be a clue i.e. the correct answer should not be the longest 7. All items should be plausible. Avoid items too obviously wrong. 8. Reduce to a minimum or 0 the use of special alternatives like ‘All of the above’, None of the above’, A and C are correct, etc. 9. Avoid the use of interdependent answers, that is: only if one answer is correct it is possible to answer another correctly Questions with ‘all of the above’ should not be abused of, but they may be useful to drawing the student’s attention towards some aspects they may overlook or that we know are frequent sources of error. In this case they become good questions for self-evaluation sessions. In this book it is avoided to show questions that in the leading statement have expressions like ‘except’, ‘it is not correct’, etc. There will always be one correct answer item. To my mind it is counter to good sense making the correct answer a false statement and I think it may even add to confusion as a component of the question. Making questions in Biochemistry for evaluation of medical students The following suggestions may help teachers to make questions to evaluate medical students of Biochemistry. Obviously, they do not exclude others more elaborate and complex. Nevertheless, their usefulness may derive from the fact that in most instances, university teachers of the subject are in the job mainly by being experts in Biochemistry rather than experts on education. Evaluation in Biochemical themes often involves questions on the following aspects of the subject: 1. MOLECULES: Characteristics that make some molecules stand out due to some aspects of their structure or function or in some cases the relationship between the two. Metabolic intermediates, energy-reserve molecules, enzymes, transporters, storage-association, genetic expression, etc. 2. PROCESSES: Digestion and absorption of nutrients, transport mechanisms through membranes, storage, genetic expression, signal transduction, etc. 3. METHODS: Techniques and procedures used to achieve biochemical knowledge. On all these it is possible to inquire about their: 1. REGULATION: Ways to regulate enzyme activity and processes. Role of hormone-generated signals. 2. STRUCTURE: Outstanding aspects of molecular structure, mainly those related to their function. 3. LOCALIZATION: Subcellular, cell or tissue location of enzymes and/or processes. 4. INTER RELATION of processes among them, according to the physiological situation, location, etc. 5. ENERGY AND EQUILIBRIUM: Thermodynamic aspects related to reactions 6. FUNCTION: Role of a molecule or enzyme, a reaction or process in cellular function. It may also be useful to be guided in what is to be asked by what is expected in the answer. It may be: 1. DEFINE Group by categories and subcategories Identify essential properties 2. COMPARE: Establish similarities and differences 3. DESCRIBE Enumerate qualities, properties, characteristics of the object or phenomenon being described 4. EXPLAIN Establish causal relationships Establish conditional judgement (of the sort If…then…) Of course, the kind of question depends on the expected achievement, of objectives or competences to be evaluated. Some associations are easier than others to establish. In multiple-choice evaluation this organization of the aspects to be evaluated will help in the choice of items, drawing attention to certain points. Examples Example A: DEFINE THE STRUCTURE OF A MOLECULE Identify the following functional group: a) Aldehyde b) Carboxyl c) Hydroxyl d) Ester e) Ketone Example B: EXPLAIN WHEN A REACTION IS AT EQUILIBRIUM A chemical reaction is at equilibrium when: a) initial speed is the same as final speed b) velocities of formation of reactants and products are equal c) all reactants have become products d) concentrations of reactants and products are equal e) the speed of product formation is greater than that of products Example C: A combination TO DEFINE THE STRUCTURE AND FUNCTION OF A MACROMOLECULE Bacterial structures known as plasmids are: a) two-chain DNA molecules b) extrachromosomal DNA molecules c) copied many times in each cell division d) molecules carrying genes (that confer antibiotic resistance to bac e) all of the above Section Three Multiple choice questions On Structure of amino acids and proteins 1) Alanine’s lateral chain (-CH3) is classified as: a) aromatic b) polar c) non polar d) acid e) basic A1 2) In the following ionization reactions of functional groups of amino acids: R-COOH →R-COO- + H+ R-NH2 + H+→ R-NH3+ a) R-COO- is the conjugate base of R-COOH b) R-COOH and R-NH2 are non dissociated acids c) R-COO- y R-NH3+ are conjugated bases d) R-NH3+ is the conjugate base of R-NH2 e) R-COOH y R-NH2 are conjugated bases A2 3) What is the net charge of glycine at pH = 6? pK COOH= 2,3 ; pK NH3+ =9,7 a) -1 b) 0 c) -2 d) +1 e) 2 A3 A1 C← A2 A ← A3 B ← 4) Which of the following forms of Arginine predominates at pH 7? a) A b) B c) C d) D e) E A4 5) Peptide: ala-glu-ser-lys-gly will bind to an anion exchange resin at pH: a) 13 b) 7 c) 5 d) 1 e) equal to the peptide’s pH A5 A4 C← A5 A ← 6) In electrophoresis, which of the following peptides will migrate to the cathode at pH 7? a) ala-glu-ser-phe-gly (A-E-S-F-G) b) asp-gly-glu-ser-asp (D-G-E-S-D) c) tyr-ser-tyr-thr-ser (Y-S-Y-T-S) d) ala-leu-ile-gly-val (A-L-I-G-V) e) his-arg-tyr-lys-val( H-R-Y-K-V) A6 7) At pH 7, which of the following forms of glutamate prevails? a) A b) B c) C d) D e) E A7 A6 E← A7 C ← 8) The binding of oxygen to Hb: a) Is favored by a decrease in pH b) displaces the proximal histidine residue to the plane of the heme ring c) brings about the oxidation of heme from ferrous to ferric d) Is favored by 2,3 biphosphoglycerate e) brings about the formation of inter and intramolecular salt bridges A8 9) In proteins, primary structure refers to the: a) amino acid sequence b) subunit contents c) tridimensional conformation d) alfa helix or beta pleated sheet contents e) salt bridges and disulfide bonds contents A9 10) Tertiary structure of proteins is stabilized by means of a) hydrogen bonds b) salt bridges c) van der Waals’ forces d) disulfide bonds e) all of the above A10 A8 B← A9 A ← A10 E ← 11) The unfolded protein response (UPR) may include: a) decrease in protein synthesis b) stimulation of the synthesis of more chaperon proteins c) bring about the degradation of badly folded proteins d) induce cellular apoptosis e) all of the above A11 12) Chaperonins are proteins that recognize badly folded proteins by means of regions that are: a) hydrophobic and exposed to the aqueous environment b) rich in positively charged amino acids that bind to ATP c) randomly folded d) folded as beta when they should be alpha helical A12 13) An Unfolded Protein Response (UPR) may arise in: a) viral infections b) parasite infections c) fever d) obesity e) all of the above A13 A11 E← A12 A ← A13 E ← On Enzymes 14) The graph below represents the relationship between concentration of glucose and the velocity of the reaction catalized by hexokinase: Glucose +ATP → glucose 6 P + ADP Identify what is represented by each number a) 1= Vmax; 2= KM; 3= ½ Vmax b) 1= Vmax; 2 = ½ Vmax; 3= 1/2 [S] c) 1= Vmax; 2= ½ Vmax; 3= KM d) 1= KM; 2= ½ Vmax; 3= Vmax e) 1= Vmax; 2= ½ KM; 3= KM A14 15) Enzymes catalyze reactions because they decrease the: a) velocity of formation of the ES complex b) reaction’s energy of activation c) velocity of dissociation of the EP complex d) difference in energy existing between reactans and products e) reaction’s Keq A15 A14 D← A15 B ← 16) An international unit of an enzyme is the amount of: a) enzyme that transforms 1 μmol de substrate per minute per mg de protein b) substrate that can be transformed per molecule of enzyme per second c) enzyme that transforms 1 mol of substrate per second d) enzyme that transforms 1 μmol of substrate per minute e) enzyme total present in a sample A16 17) Trypsin is secreted as a precursor of the type known as zymogens, characterized by being: a) multiple forms of the same enzyme b) activated by covalent irreversible modification c) denatured enzymes d) activated when they join their apoenzyme e) enzymes that have no prosthetic group A17 18) The following reaction is catalized by a transaminase, which belongs to the group of: a) hydrolases b) transferases c) lyases d) ligases e) isomerases A18 A16 D← A17 B ← A18 B ← 19) In a metabolic pathway, the enzyme proportionally least limiting the velocity is that which: a) is at the beginning of the pathway b) catalyzes an irreversible reaction c) catalyzes reactions that are near equilibrium d) shows low activity due to a high K or low Vmax M e) is present in low concentration A19 20) In an enzymatic reaction, a non-competitive inhibitor: a) diminishes KM b) diminishes Vmax c) diminishes KM and Vmax d) does not affect Vmax e) augments KM A20 21) Relating to kinetic characteristics of an enzymatic reaction, it is correct to assert that: a) KM is a measure of the velocity of reaction b) Vmax is reached when enzyme and substrate concentrations become equal c) ½ de Vmax is reached when S is equal to KM d) Vmax is independent from enzyme concentration e) KM is equal to 1/S which is the point when ½ Vmax is reached A21 A19 C← A20 B ← A21 C ← 22) Phosphofructokinase I is an allosteric enzyme, so it follows that its active site: a) may suffer modifications in amino acid sequence due to regulating metabolites b) has little specificity for the substrate, which gives the enzyme its regulatory character c) besides the substrate, it can recognize some regulating metabolites d) can be spatially reorganized when a regulator molecule binds to the enzyme A22 23) The conversion of trypsin zymogen into the active enzyme is achieved through: a) covalent irreversible changes b) covalent reversible changes c) non-covalent modifications d) allosteric modulation A23 24) Regulation of enzymatic activity through irreversible covalent modification implies: a) hydrolysis of specific peptide bonds b) binding of components at points different from the active site c) phosphorylation d) breaking of disulphur bridges e) polymerization of multienzymatic complexes A24 A22 E← A23 A ← A24 D ← 25) When glucose concentration is equal to KM of hexokinase, the velocity of reaction is: a) Vmax b) 0,5 Vmax c) 2 Vmax d) numerically equal to KM e) the initial velocity A25 26) In the following representation of Lineweaver-Burk’s equation, what does point a represent? a) KM b) 1/ KM c) - KM d) -1/ KM e) 1- KM A26 27) KM of glucokinase is ~ 7 mM. When the concentration of glucose is much lower than that value, the reaction’s velocity is: a) equal to maximum velocity b) proportional to substrate concentration c) half maximum velocity d) very slow e) cannot be measured A27 A25 B← A26 A ← A27 B ← 28) Which one of the following is an indispensable condition for the reaction to proceed? Glucose + ATP → glucose 6P + ADP + Pi ΔG°’= -4,0 kJ mol-1 a) increase the concentration of ATP b) increase the temperature c) presence of hexokinase d) hydrolysis of ATP e) increase the concentration of glucose A28 29) The velocity of the immense majority of reactions inside cells will depend on the: a) ∆G value b) Keq value c) presence of an enzyme d) concentration of products e) concentration of reactants A29 30) The maximum velocity of an enzymatic reaction depends on the: a) proportion of molecules in transition state b) affinity of the enzyme for its substrate c) value of the equilibrium constant d) concentration of substrate e) ΔG° of the reaction A30 A28 C ← Despite the reaction having a negative ∆G, it will not proceed at any detectable speed unless an enzyme is present. Whence the importance of always making sure an enzyme is present when depicting intracellular reactions. A29 C← A30 A ← 31) Coenzymes supply the enzymatic reactions in which they participate with: a) a regulatory site for the enzyme activity b) stability for the enzyme-substrate complex c) a functional group participating in catalysis d) the necessary energy to reach the transition state A31 32) A substrate and an allosteric regulator of a given enzyme have in common that they: a) bind covalently to their respective sites in the enzyme b) determine conformational changes on the enzyme c) are found in equimolar concentrations d) are modified during the reaction A32 33) An inhibitor is more specific a) the more it resembles the substrate b) If it binds covalently to the enzyme c) It binds covalently to the functional groups of the active site of the enzyme d) If it impairs efficiently the binding of the substrate to the enzyme A33 A31 C← A32 B ← A33 A ← 34) In an enzymatic reaction the transition state is characterized by: a) the substrate is its maximum molecular distortion state b) both enzyme and substrate are in a distorted electronic configuration c) having an unstable electronic configuration d) having a high energetic level e) all of the above A34 35) Statins share in their structure the following chemical They are drugs used to inhibit hydroxymethyglutaryl coenzyme A reductase (HMG-CoA reductase) an enzyme participating in cholesterol synthesis by catalysis of this reaction: What kind of inhibition is that of statins over HMG-CoA reductase?: a) allosteric b) acompetitive c) non-competitive d) competitive A35 A34 E← A35 D ← 36) pH changes affect reactions catalized by enzymes because they produce changes in the ionization of: a) amino acid residues involved in the binding of the substrate b) amino acid residues involved in catalysis c) substrate groups d) amino acid residues involved in enzyme stability e) all of the above A36 37) The Michaelis-Menten constant (KM) is: a) low for enzymes having a greater Vmax b) numerically equal to the equilibrium constant for the reaction of dissociation of the complex (E-P) to E + P c) the substrate concentration at which v = ½ Vmax d) higher the higher the affinity of the enzyme for the substrate e) all of the above A37 38) Generally speaking, regulatory enzymes catalyze reactions: a) at the beginning of metabolic pathways b) at branching points of metabolic pathways c) far from chemical equilibrium d) whose velocity is modified by small changes in substrate concentration e) all of the above A38 A36 E← A37 C ← A38 E ← 39) In clinical lab results enzyme activity is generally reported as: a) Specific activity b) International units c) Enzymatic activity d) Catalytic activity e) katals A39 40) The specificity of the reaction catalized by an enzyme is determined by: a) the chemical structure of the substrate b) the amino acid residues in the active site c) its KM value d) its sensitivity to regulatory mechanisms A40 On Cell Biology 41) DNA and RNA polymerases have in common: a) the need for a DNA template b) direction of synthesis (5´ →3´) c) liberation of pyrophosphate as a product d) catalysis of ester bond formation e) all of the above A41 A39 C← A40 B ← A41 E ← 42) Sterol accumulation in the plasma membranes is a characteristic of cells that are: a) apoptotic b) malignant c) in phase S of the cell cycle d) foam cells e) stem cells A42 43) In order to incorporate the genetic information contained in an mRNA to a bacterial genome it is indispensable to use: a) the enzyme reverse transcriptase b) a plasmid c) the enzyme DNA ligase d) a restriction endonuclease e) all of the above A43 44) Restriction enzymes: a) hydrolyze phosphodiester bonds in all types of nucleic acids b) require a free 3’ –OH for their activity c) pull apart the two chains of DNA in specific regions d) have editing function e) are specific for pulling apart DNA chains in regions separating genes A44 A42 D← A43 E ← A44 C ← 45) The correct sequence in the transference process called ‘southern blot’ is: a) alkaline dissociation of DNA to separate the strands, electrophoresis in agarose gel, digestion by a restriction enzyme, transfer to a nitrocellulose membrane b) digestion of DNA by a restriction enzyme, alkaline dissociation to separate the strands, electrophoresis in agarose gel, transfer to a nitrocellulose membrane c) digestion of DNA by a restriction enzyme, electrophoresis in agarose gel, alkaline dissociation to separate the strands, transfer to a nitrocellulose membrane d) alkaline digestion to separate strands, digestion with a restriction enzyme, electrophoresis in agarose gel, transfer to a cellulose membrane e) digestion of DNA by a restriction enzyme, electrophoresis in a nitrocellulose membrane, alkaline dissociation to separate strands, transfer to an agarose gel A45 46) Bacterial structures called plasmids are: a) double stranded DNA molecules b) extrachromosomal DNA molecules c) copied many times in each cell division. d) gene carriers that confer antibiotic resistance to bacteria. e) all of the above A46 A45 C← A46 E ← 47) To perform a polymerase chain reaction (PCR) it is indispensable to have: a) a DNA template b) deoxyribonucleotides c) RNA primers d) tag polymerase e) all of the above A47 48) The PCR reaction in real time is different from conventional or standard PCR because it: a) needs recently extracted DNA b) does not amplify DNA but RNA c) is more efficient, but slower than conventional d) allows quantification of the amplified product e) may be used to determine the sequence of the amplified product A48 49) The following reaction:....C-C-U-A-U-C-OH- →..C-U-A-U-OH + C Is catalized by: a) DNA polymerase I b) helicase c) gyrase d) DNA ligase e) 3´-5´ exonuclease A49 A47 E← A48 D ← A49 E ← 50) If transcription of the DNA fragment depicted below were from left to right.... ATTCAG..... 5´....TAAGTC...… The sequence of the resulting RNA fragment would be: a) 5´....GACUUA... b) 5´....ATTCAG.... c) 5´....AUUCAG.... d) 5´....UAAGUC.... e) 5´....CTGAAT.... A50 51) Analysis of a nucleic acid fragment results in adenine concentration different from that of thymine and guanine different from cytosine, the conclusion would be: a) double helix DNA b) double helix RNA c) single stranded RNA d) single stranded DNA e) messenger RNA A51 A50 C← A51 D ← 52) In the process of protein synthesis: a) each amino acid recognizes its place on mRNA owing to its specific structure b) the binding of ribosomal RNA to mRNA is possible due to their bases homology c) each amino acid binds selectively to the anticodon of a specific tRNA d) the place of each amino acid in the chain is determined by the mRNA sequence e) all of the above A52 53) Given the following sequence of mRNA, choose which tRNA will be next to incorporate: a) 1 b) 2 c) 3 d) 4 e) 5 A53 A52 D← A53 B ← 54) Replication is said to be semiconservative because: a) DNA polymerase III does not make mistakes b) each new resulting double helix is made up of one original strand and a new one c) only one of the strands is conserved by replication d) DNA polymerase I makes a mistake every 100 million bases e) each of the four resulting chains is made by 50 per cent DNA of original chains and fifty percent of new DNA A54 55) In order to obtain mRNA from a given cell type affinity chromatography may be used joining the matrix to a polynucleotide with a base sequence: a) poly U b) complementary to the introns c) repetitive o initiation codons d) repetitive of initiation anticodons e) in which phosphate is replaced by another polyvalent cation A55 56) Highly repetitive DNA is made up of sequences that go from hundreds to millions of copies that: a) are the regions recognized by transcription factors b) guarantee there are enough copies of the constituting genes c) codify only for rRNA and tRNA d) codify for histones e) are not transcribed A56 A54 D← A55 A ← A56 E ← 57) Tetracyclines are antibiotics capable of inhibiting: a) peptidyl transferase b) the start of translation c) the cell cycle d) the activation of amino acids A57 58) If a sample of double stranded DNA has 20% moles of guanine, what would be the percentage of moles of thymine? a) 20% b) 30% c) 40% d) 80% e) not known. Insufficient data A58 59) In prokaryotes, as translation proceeds the growing polypeptide chain remains bound to the ribosome through: a) an amino acid-bearing protein b) ribosomal 5S RNA c) a segment of mRNA d) an aminoacyl-tRNA e) peptidyl transferase A59 A57 B← A58 B ← A59 D ← 60) Which of the following antibiotics inhibits peptidyl transferase? a) streptomycin b) rifamycin c) actinomycin D d) tetracycline e) chloramphenicol A60 61) In eukaryotes one of the characteristics of mRNA that differentiates it from ribosomal and tRNA is: a) to have a poly A tail b) being synthesized in the nucleus c) be modified after transcription d) to have methylated bases e) to have double-helix regions A61 62) How many amino acids will have the peptide product of the expression of the following polydeoxyribonucleotide? 5´-CCTACCGCGGAATCATTAACAT-3´ Start codon = AUG a) 4 b) 5 c) 6 d) 7 e) 8 A62 A60 E← A61 A ← A62 A ← 63) Transcription of an eukaryotic gene may give rise to: a) an oligomeric protein b) a polypeptide c) several polypeptides d) a ribonucleic acid e) a double stranded chain of DNA A63 64) During replication, helicase acts: a) stabilizing the replication bubble b) avoiding DNA supercoiling c) hydrolyzing phosphodiester bonds in the direction 5´ → 3´ d) breaking hydrogen bonds between base-pairs of DNA e) recognizing the promoter site A64 65) It is said that the genetic code is partially degenerate because: a) there are amino acids not codified by any codon b) some codons do not codify for any amino acid c) an amino acid has the same codon in all species d) a codon may codify for more than one amino acid e) an amino acid may have several codons A65 A63 D← A64 D ← A65 E ← 66) The high fidelity of the process of protein synthesis is due mainly to: a) the activity of peptidyl transferase b) coupling between the ribosome and transfer RNA c) the correction activity of aminoacyl-tRNA synthetase d) the presence of initiation and elongation factors la for each aminoacyl-tRNA e) all of the above A66 67) Bearing in mind that according to the genetic code, each one of the following codons determines the incorporation of the amino acid at its right: UUU phenylalanine (F) AAA lysine (K) AAU asparagine (N) AUA isoleucine (I) UUA leucine (L) UAU tyrosine (Y) Then, if in an in vitro system for protein synthesis artificial poly (UA) is used as messenger RNA it would be expected that peptides formed will contain: a) phenylalanine (F) and lysine (K) b) asparagine (N) and lysine (K) c) phenylalanine (F) and leucine (L) d) polyleucine (L) e) tyrosine (Y) and isoleucine (I) A67 A66 C← A67 B ← 68) DNA ligase catalyzes the: a) incorporation of deoxyribonucleotides in order to join DNA fragments b) formation of hydrogen bonds to join both chains of DNA after replication c) formation of phosphodiester links that close DNA interruptions d) joining of primer and DNA to start replication A68 69) In the process of protein synthesis: a) each amino acid recognizes its place in mRNA thanks to its specific structure b) each codon anticodon pair must have identical sequence to avoid reading errors c) binding of mRNA to ribosomal RNA is possible due to the similarity of bases d) each amino acid binds selectively to the anticodon of its specific tRNA e) the placement of each amino acid depends on the codons of mRNA A69 70) Genomic imprinting is: a) expression of genes that cause diseases b) presence of certain genes in the genome c) differential expression of one of the alleles d) absence of certain genes from the genome e) presence in the genome of genes that allow individual identification A70 A68 C← A69 E ← A70 C ← 71) Polymorphisms are certain DNA sequences that: a) codify for proteins that the human species shares with other species b) vary among individuals c) are repetitive d) are palindromes A71 72) Proto-oncogenes codify for proteins that: a) repair DNA b) suppress tumor growth c) deliver a signal for apoptosis d) regulate the proliferation and growth of cells A72 73) Among transcription factors motifs may be found: a) helix-turn-helix b) helix-loop-helix c) zinc finger d) leucine zippers e) all of the above A73 74) DNA replication in cell is carried out: a) to guarantee there is protein synthesis b) when there is stimulus for cell division c) as a step previous to transcription d) as a consequence of mitosis e) when cells grow old A74 A71 B← A72 D ← A73 E ← A74 B ← 75) The function of DNA replication is a) to guarantee the supply of enough copies of regulatory genes for transcription b) the supply of enough sites for the start of transcription c) mitosis to take effect d) all of the above A75 76) Epigenetic modifications include: a) changes in the structure of nucleosomes b) synthesis of interference RNAs c) methylation of DNA bases d) all of the above A76 77) Alleles are: a) different forms of the same gene b) copies of the same gene within a chromosome c) each of the complementary chains of a gene d) all the genes given by one of the parents A77 78) Transgenic organisms: a) those in which a gene is deleted b) express genes from a different organism c) present mutations induced in their own genes d) are induced to increase the transcription of a gene A78 A75 C← A76 E ← A77 A ← A78 B ← 79) Deacetylation of histones by situins (enzymes with deacylase activity) brings about: a) favored binding to DNA b) impaired transcription of some genes c) favored DNA organization in nucleosomes d) all of the above A79 80) Shortening of chromosomes as a result of repeated cell divisions is a consequence of the a) progressive cell aging b) increased expression of telomerase in aged cells c) need of a primer for DNA polymerases activity d) progressive loss of the repair ability of DNA polymerase I A80 81) Telomerase is a: a) primase b) exonuclease c) endonuclease d) reverse transcriptase A81 82) Interference RNA is a double helix RNA that: a) contains sequences complementary to some mRNAs b) contains information for the synthesis of transcription factors c) impairs transcription of some genes d) participates in the removal of introns in RNA e) mimics the structure of tRNAs impairing their binding to the ribosome A82 A79 C← A80 C ← A81 D ← A82 A ← 83) DNA methylation is different from histones acetylation in that the former: a) impairs the formation of nucleosomes b) is a signal for the corrective activity of DNA polymerase I c) contributes to recognition of sensitive regions of restriction endonucleases d) does not change the DNA sequence but is inheritable e) impairs the initiation of transcription A83 84) The process of transcription: a) happens after DNA replication b) depends on the type of cell c) does not depend on supply of ATP d) allows a single RNA to give rise to different proteins A84 85) In paternity tests, any cell from the alleged child may be used because: a) the selection of DNA segment to study depends on the type of primer used b) in all cells there are enzymes capable of synthesizing DNA c) the DNA polymerase used in the PCR test is not very specific d) all cells have the same genetic charge A85 A83 E← A84 D ← A85 D ← 86) Microsatellites are: a) small DNA fragments repeated in consecutive fashion b) DNA fragments found at the chromosomes’ extremes c) DNA fragments that join the chromosomes’ arms d) DNA fragments able to go from one point to another in the chromosome A86 87) Microsatellites are useful in individual identification studies because they are: a) easily accessible from a technical point of view b) small fragments c) polymorphic d) inheritable e) more abundant in sexual chromosomes A87 88) According to the WHO, the principal cause of proliferation of resistant bacterial strains to antibiotics is the a) inadequate use of antibiotics b) high frequency of DNA mutations in bacteria c) high frequency of transmission of plasmids among bacteria d) high mobility of human populations e) loss of vaccination effectiveness A88 A86 A← A87 C ← A88 A ← 89)A point mutation is: a) the change of a nitrogen base by another in the base sequence of DNA b) the elimination of a single nitrogen base in the sequence of bases of DNA c) the addition of a single nitrogen base to the sequence of bases of DNA d) the substitution of a single amino acid by another in the amino acid sequence of a chain of protein A89 On Membranes 90) Kt for the erythrocyte glucose transporter (GLUT 1) is approximately 2mM and that of the beta cell transporter (GLUT 2) is approximately 10mM. If the glycemia value is 5mM, the transport speed: a) is greater in the erythrocyte than in the beta cell b) is half of the maximum for GLUT 2 c) by GLUT 1 decreases because it is saturated d) of GLUT 2 may increase but not that of GLUT 1 A90 91) Simple diffusion and facilitated diffusion have in common that they: a) possess rectangular hyperbolic kinetics b) are done in a favorable gradient c) may reach saturation d) are specific e) all of the above A91 A89 A← A90 D ← A91 B ← 92) The fluidity of the cell membrane: a) decreases with increasing length of the chain of the fatty acids present b) depends on its protein content c) is inversely proportional to the permeability of the membrane d) increases with the amount of transporters present in it e) increases with the degree of unsaturation of the fatty acids present A92 93) The carbohydrates present in the plasma membrane determine the function of proteins that act as: a) enzymes b) receptors c) transporters d) recognition proteins e) signal transducing proteins A93 A92 E← A93 D ← 94) The following is a representation of the absorption of glucose in the intestine. His analysis allows us to conclude that it is done by: a) two types of transporters b) two different types of transport c) a cotransporter d) its coupling to a sodium gradient A94 95) A solution is isotonic with respect to the plasma when it has the same: a) glucose concentration b) sodium chloride concentration c) ion concentration plus glucose d) osmolarity e) amount of solutes A95 A94 B← A95 D ← 96) The passage of substances through channels in the plasma membrane differs from the passage through transporters in that: a) it is less specific b) it is not saturable c) can be affected by voltage changes d) always occurs in favor of a gradient e) the channels are not always protein structure A96 97) The following graph represents the kinetics of the transport of two substances through the membrane, its analysis leads to the conclusion that: a) the transport of A is more specific than that of B b) the transport of A is active and that of B passive c) the transport of B is active and that of A passive d) both transports can be saturated e) both A and B are transported by a favorable gradient A97 A96 C← A97 D ← 98) Which of the following goes across the membrane in the process of osmosis: a) water b) gases c) glucose d) small solutes e) all of the above A98 99) Cholesterol is an essential component of membranes because: a) participates in some systems of cotransport b) prevents the formation of bumps in the lipid bilayer c) protects its integrity d) facilitates the incorporation of some proteins e) acts regulating its fluidity A99 100) Lipid rafts are structures of the plasma membrane that: a) do not have cholesterol b) are rich in unsaturated fatty acids c) are microdomains related to signal transduction d) have more fluidity than the rest of the membrane e) all of the above A100 A98 A← A99 E ← A100 D ← 101) Lidocaine hydrochloride is a local anesthetic that, in addition to its anesthetic effect, can cause other changes in cells, depending on dose and the route of administration. Based on the analysis of its formula, which statements can be true regarding lidocaine: a) it has an amphipathic nature b) it can be incorporated into cell membranes c) it can interfere with signal transduction d) it can cause dysfunction of the electronic transport chain e) all of the above A101 On Introduction to Metabolism and Signal Transduction 102) The mechanisms regulating enzymatic activity both allosteric and covalent, reversible and irreversible have as a common effect that they a) alter the enzyme’s charge b) change the active site conformation c) require the participation of other enzymes d) change the primary structure of the enzyme e) bring about changes in quaternary structure of the enzyme A102 A101 E← A102 B ← 103) Anabolic and catabolic pathways share this characteristic: a) they happen until equilibrium is reached b) their ∆G values are negative c) acetyl-coA is a common intermediary d) each one has specific regulatory mechanisms A103 104) Regulation of metabolism is advantageous because: a) allows hormones to exert their action b) limits the number of reactions necessary for each metabolic pathway c) determines energy saving d) prevents all reactions from reaching equilibrium A104 105) Hormones may influence metabolism in effector cells by producing: a) changes in the speed of protein synthesis b) activation or inhibition of some enzymes c) changes in permeability of the plasmatic membrane d) epigenetic modifications e) all of the above A105 106) Hormones involved in cellular energetic metabolism: a) promote its reaching equilibrium b) allow the body to stay away from equilibrium c) are liberated in response to equilibrium alterations d) are the only way of affecting the equilibrium constants of reactions catalized by regulatory enzymes A106 A103 B← A104 D ← A105 E ← A106 B ← 107) One of the mechanisms trough which insulin affects cAMP concentration in effector tissues is: a) inhibition of protein GEF (guanine nucleotide exchange factor) b) stimulation of protein GDI (guanosine nucleotide dissociation inhibitor) c) stimulation of phosphodiesterase d) increase in the concentration of metabolites inhibiting adenyl cyclase A107 108) The result of the stimulation G proteins may be the intracellular liberation of: a) cAMP b) cGMP c) IP3 d) ionic calcium e) all of the above A108 109) Effector systems of the action of hormones include: a) stimulation of an enzymatic activity of the receptor b) activation of G proteins c) opening of the ionic canals d) regulation of gene transcription e) all of the above A109 A107 C← A108 E ← A109 E ← 110) Cessation of G proteins activation happens when: a) the hormone separates from the receptor b) an G-inhibiting protein is activated c) cAMP is hydrolyzed d) alpha subunits separate e) GTP bound to the alfa subunit is hydrolyzed A110 111) As a consequence of the action of cholera toxin: a) the concentration of intracellular cAMP decreases b) the dissociation of the subunits of G protein is inhibited c) protein kinase A becomes inactive d) phosphodiesterase becomes inactive e) the alpha subunit of G protein loses its GTPase activity A111 112) Steroid hormones act at the cellular level: a) inhibiting pre existing enzymes b) through a second messenger c) by regulating gene expression d) through G proteins e) modifying the concentration of intracellular ionic calcium A112 113) G proteins: a) act as receptors for some hormones b) are signal transductors through the membranes c) synthesize intracellular second messengers d) catalyze la synthesis of cAMP from ATP e) act as intracellular messengers for some hormones A113 A110 E← A111 E ← A112 C ← A113 B ← 114) Steroid hormones are characterized because a) they bind to specific genes in DNA modifying their transcription b) when binding to their receptor they increase its affinity to DNA c) affect transcription by regulating the activity of RNA polymerase d) bind to the mRNAs that codify for some proteins inhibiting its degradation A114 115) A common characteristic to all oncogenes is that they codify for proteins that: a) are viral b) are tumor markers c) impair the emergence of tumors d) intervene in signal transduction e) have abnormal folding due to mutations A115 116) Protein kinases A and C have in common that they: a) are membrane proteins b) are allosterically activated c) depend on ionic calcium for their activation d) are activated by alpha subunits of G proteins e) all of the above A116 A114 B← A115 D ← A116 B ← 117) Kinases dependent on AMP and cAMP have in common that: a) their activity depends on the ‘energetic charge’ of the cell b) they are activated as a response to glucagon c) they can be phosphorylated d) they are serine kinases A117 On Krebs cycle and oxidative phosphorylation Is spite of widespread opinion among doctors and students that it is useless to know the reactions of the Krebs cycle, many alterations seen in diabetes mellitus are related to the cycle; the same is true for metabolic adaptations during fasting or following food ingestion. 118) With the exception of citrate synthase, enzymes regulating the speed of the Krebs cycle have in common that they: a) catalize negative ΔG°’ reactions b) catalize oxidation-reduction reactions c) function with catalytic levels of substrate d) catalize oxidative decarboxylation reactions + e) are regulated allosterically by the concentration of NAD A118 A117 D← A118 C ← 119) During a fast, in spite of increased activity of pyruvate carboxylase, the concentration of oxaloacetate inside liver mitochondria stays low because: a) it passes through the mitochondrial membrane into the cytoplasm b) the speed of the Krebs cycle is increased c) it is used to make aspartate, compensating for the amino acid deficit provoked by fasting d) most of it serves as a substrate for citrate synthase to form citrate that constantly exits the mitochondria in that situation e) the Keq of the reaction catalized by malate dehydrogenase favors accumulation of malate A119 120) A patient of chronic alcoholism may present a thiamine deficiency (B1 vitamin), because alcohol inhibits its intestinal absorption. In this case the functioning of which enzyme would be impaired? a) glutamate dehydrogenase b) succinate dehydrogenase c) isocitrate dehydrogenase d) pyruvate dehydrogenase e) malate dehydrogenase A120 A119 E← A120 D ← 121) Which of the following Krebs cycle enzymes is located in the internal mitochondrial membrane? a) malate dehydrogenase b) isocitrate dehydrogenase c) α-ketoglutarate dehydrogenase d) succinate dehydrogenase e) citrate synthase A121 122) The fact that ΔG°’ of the reaction catalized by malate dehydrogenase is +7,0 kcl.mol-1 implies that: a) it is a regulatory enzyme of the Krebs cycle b) it allows the interrelation of the Krebs cycle with other metabolic pathways c) the reaction is exergonic d) its Keq is larger than 1 e) at equilibrium, malate production predominates A122 123) Which of the following Krebs cycle reactions is associated to the production of NADH + H+?: a) succinyl-CoAà succinate b) acetyl-CoA + oxaloacetate à citrate c) malate à oxaloacetate d) citrate à isocitrate e) succinate à fumarate A123 A121 D← A122 E ← A123 C ← 124) The Krebs cycle is considered an amphibolic pathway because: a) its intermediaries are precursors for metabolic pathways b) it functions as final way of cell catabolism c) its metabolites participate in the cell’s anabolism as well as catabolism d) it is present in all cell of the body e) all its reactions are reversible A124 125) In the Krebs cycle, anaplerotic reactions are those catalized by the enzymes: a) citrate synthase and glutamate dehydrogenase b) pyruvate dehydrogenase and malate dehydrogenase c) pyruvate dehydrogenase and pyruvate carboxylase d) glutamate dehydrogenase and pyruvate carboxylase e) glutamate dehydrogenase and pyruvate dehydrogenase A125 126) When oxidative phosphorylation is uncoupled oxygen consumption: a) accelerates but phosphorylation of ADP is unaffected b) increases and phosphorylation of ADP ceases c) ceases but phosphorylation of ADP is unaffected d) ceases and phosphorylation of ADP decreases e) and phosphorylation of ADP increase A126 A124 C← A125 D ← A126 B ← 127) The Chemiosmotic theory of oxidative phosphorylation contends that: a) the energy of a proton gradient is utilized for the synthesis of ATP b) an electron gradient is generated at the internal mitochondrial membrane c) hydrolysis of ATP is used for the formation of an energy rich proton gradient d) protons accumulate in the mitochondrial matrix and are then pumped out through the complex Fo-F1 e) gradients of electrons as well as protons are generated on both sides of the internal mitochondrial membrane A127 128) Substrate-level phosphorylation requires: a) the oxidation of NADPH instead of NADH b) the formation of an electron gradient c) inhibition of the respiratory chain. d) a high energy charge inside the cell e) the formation of a high energy intermediary A128 129) ATP synthesized in mitochondria: a) diffuses freely to the outside of mitochondria b) exits from them through the Fo-F1 ATPase complex c) is transported to the cytosol by a protein in exchange for ADP d) is actively expelled to cytosol by an energy-requiring pump e) is transported to the cytosol by a protein coupled to the Na+/K+ pump A129 A127 A← A128 E ← A129 C ← 130) Identify the oxidizing agent in the following reaction (E= enzyme): NADH + H+ + E-FMN ↔ NAD+ + E-FMNH2 a) NADH + H+ b) E-FMN c) NAD+ d) E-FMNH2 A130 131) Given the following reaction and its ΔGº value A+C→B+D ΔGº = -15 kcal/mol It can be inferred that: a) its equilibrium constant is greater than 1 b) it will only happen if coupled to an exergonic reaction c) the products have more free energy than the reactants d) it does not require a catalyst e) it has a high velocity of reaction A131 132) ATP is a high energy compound because: a) in its structure there are easily transferable phosphate groups b) its ionic character confers to the molecule an electronic distribution favoring hydrolysis c) Its energy of hydrolysis is –7 kcal/mol d) Its hydrolysis products are more stable e) all of the above A132 A130 B← A131 A ← A132 E ← 133) Cytochromes are: a) hydrogen atoms transporters b) proton acceptors c) hydrure ions acceptors d) electron acceptors A133 134) Phosphorylation of complex IV in the mitochondrial electron transport chain by protein kinase A: a) allows its inhibition by ATP b) stimulates electron transport c) facilitates its activation by AMP d) triggers uncoupling of oxidative phosphorylation A134 135) An uncoupling molecule might be used to bring about weight loss because: a) heat would be liberated, accelerating metabolism b) there would be heat liberation, favoring fatty acid mobilization through the mitochondrial membrane c) part of the energy coming from food oxidation would be dissipated as heat d) all of the above A135 A133 D← A134 A ← A135 C ← 136) Atractyloside interferes with the synthesis of ATP in the mitochondrion because it: a) inhibits the transference of electrons between cytochromes b and c1 b) inhibits the ADP/ATP transport system c) blocks the transference of electrons at the complex IV level of the respiratory chain is a protonophore and dissipates the proton gradient d) impairs the formation of high-energy intermediates A136 137) Antimycin and rotenone act as follows: a) inhibiting transport of H+ through the Fo-F1-ATPase complex b) destroying the H+ gradient through the membrane c) blocking ATP/ADP transport d) increasing oxygen consumption e) inhibiting electron transport A137 138) When the standard free energy change of a chemical reaction is > 0: a) its Keq > 1 b) it is endergonic c) it proceeds at very low speed d) it continues until running out of substrates A138 A136 B← A137 E ← A138 B ← 139) The energetic charge of the cell is defined by the: a) energy liberated by hydrolysis of ATP and other high-energy molecules b) state of oxidation / reduction of coenzymes c) ratio ATP/ ADP + AMP d) total of high-energy compounds e) availability of oxidable substrates A139 140) Some of the reactive oxygen species (ROS): a) are active in the regulation of metabolism b) participate in immune response c) cause oxidative damage to biomolecules d) participate in the synthesis of essential molecules e) all of the above A140 141) Among ROS the most reactive is: a) superoxide anion radical (O2.-) b) hydroperoxide radical (HOO.) c) hydroxyl radical (OH.) d) hydroxide ion (OH-) e) hydrogen peroxide (H2O2) A141 A139 C← A140 E ← A141 C ← 142) It has been postulated that the damage by re perfusion after a period of ischemia is probably due to: a) increase in anaerobic oxidation of glucose during ischemia b) accumulation of NADH + H+ during ischemia c) saturation by electrons of the respiratory chain components during ischemia d) overproduction of ROS when blood flow is reestablished leading to insufficient antioxidant defense e) all of the above A142 143) α-ketoglutarate dehydrogenase and pyruvate dehydrogenase are dissimilar because: a) they catalyze irreversible reactions b) of the type of reaction that catalyze c) they use a different coenzyme d) their regulation mechanisms are different e) of their subcellular location A143 144) Ketone bodies synthesis is a way: a) of reoxidizing mitochondrial NADH b) to export reducing equivalents to peripheral tissues c) of regenerating CoA d) all of the above A144 A142 E← A143 D ← A144 E ← 145) Oxaloacetate does not pass through the internal mitochondrial membrane because: a) in its absence, all acetyl-CoA would be concerted to ketone bodies b) it is necessary to guarantee the function of the Krebs cycle c) its half- life inside the mitochondrion is too short d) there is no transporter for it in the membrane A145 146) Some reactions of the Krebs cycle: a) allow the extraction of reducing equivalents from cell fuels b) constitute the main source of CO2 in the body c) are indispensable for the conversion of carbohydrates into fat d) participate in the conversion of amino acids and lactate into glucose e) all of the above A146 147) The cyclic character of the Krebs cycle implies that: a) coenzymes can be re used b) all reactions are reversible c) requires a constant supply of acetyl-CoA d) citrate is regenerated at each round of the cycle e) malate in catalytic concentrations accelerates oxygen consumption A147 A145 D← A146 E ← A147 E ← 148) Coupling between electron transport and ATP synthesis in mitochondria is due to the: a) appearance of a proton gradient b) vector organization of the components of the respiratory chain c) existence of an inter membrane space d) structure of the FoF1 complex e) redox potential of the components of the respiratory chain A148 149) A decrease in mitochondrial ADP concentration can inhibit electron transport because: a) the energetic charge of the cell is high b) the concomitant ATP increase inhibits complex I c) the flow of protons through the FoF1 complex d) the Krebs cycle slows down A149 150) The malate shuttle allows the net transport from cytosol to mitochondria of: a) ATP b) NADH c) ketoacids d) amino acids e) reducing equivalents A150 A148 A← A149 C ← A150 E ← 151) α-ketoglutarate dehydrogenase and pyruvate dehydrogenase: a) show a negative delta G. that makes them catalyze irreversible reactions b) catalyze reactions of oxidative decarboxylation c) are regulated by the concentration of NAD+ d) are multi-enzyme complexes e) all of the above A151 152) Hydrolysis of pyrophosphate produced in a reaction may shift the equilibrium because: a) it modifies delta Gº of the reaction b) it does not require an enzyme to participate c) increases the speed of the reaction d) decreases the concentration of the reaction products e) hydrolysis pyrophosphate shows a negative ΔGº A152 153) The activity of citrate synthase is regulated by: a) phosphorylation / dephosphorylation b) allosteric inhibition by ATP c) allosteric activation by NAD+ d) retro inhibition by citrate e) inhibition by acetyl-CoA A153 A151 E← A152 D ← A153 D ← 154) A decrease in ATP/ADP + AMP ratio may increase the Krebs cycle speed because allosterically it activates: a) α-ketoglutarate dehydrogenase b) isocitrate dehydrogenase c) succinate dehydrogenase d) malate dehydrogenase e) citrate synthase A154 Metabolism of Carbohydrates 155) Which of these two names expresses best the structure of the following molecule inside the body? Lactate (C 3H5O3-) or lactic acid (C3H6O3): a) the two names represent the same molecule b) lactate, because at physiological pH it exists as its conjugate base c) lactate, because at physiological pH the lactate isomer predominates d) lactic acid because it has all the atoms derived from half a molecule of glucose A155 156) Glucose enters the erythrocyte via a transport type characterized by being: a) simple diffusion b) stimulated by insulin c) facilitated by GLUT 1 d) dependent on the supply of ATP e) facilitated by a sodium ion co-transporter A156 A154 B← A155 B ← A156 C ← 157) Glucose transport into the pancreatic beta cells is mediated by: a) GLUT1 b) GLUT2 c) GLUT3 d) GLUT4 e) GLUT5 A157 158) Which of the following glucose transporters is activated as a consequence of insulin effect? a) GLUT1 b) GLUT2 c) GLUT3 d) GLUT4 e) GLUT5 A158 159) Compared to other GLUT transporters, GLUT2: a) shows the highest kt for glucose b) is activated by insulin c) transports glucose against a concentration gradient d) co-transports sodium ions together with glucose e) is highly specific for glucose A159 A157 B← A158 D← A159 A ← 160) Hexokinase and glucokinase have in common: a) their tissue location b) their substrates and products c) being inhibited by their products d) being inducible enzymes e) all of the above A160 161) Which of the following mechanisms is involved in the regulation of glucokinase activity? a) allosteric inhibition by citrate b) phosphorylation by protein kinase A c) translocation to the nucleus d) inhibition by its product e) allosteric inhibition by ATP A161 162) The activity of glucokinase is involved in the regulation of glycaemia because: a) its activity increases in proportion to the increase in glycaemia b) favors the utilization of glucose for hepatic glycogen synthesis c) acts as a glycaemia-sensor for the beta cells in the pancreas d) restricts the increase in glycaemia after ingestion of food e) all of the above A162 A160 B← A161 C ← A162 E ← 163) In anaerobic conditions, NADH produced in glycolysis is re- oxidized through the following reaction: a) fructose 1,6-bisphosphateà glyceraldehyde-3P + dihydroxyacetone-P b) glyceraldehyde-3P à 1,3-DPG c) pyruvate à lactate d) dihydroxyacetone-P à glyceraldehyde-3P e) malate à oxaloacetate A163 164) Adenylate kinase catalyzes the following reaction, 2ADP ↔ATP + AMP that in erythrocytes is tightly linked to the activity of glycolysis, because: a) it produces AMP that reverts inhibition of PFK by ATP b) supplies AMP necessary for pyruvate kinase activity c) supplies ATP necessary for phosphorylation of glucose by hexokinase d) it is the main source of ATP for the erythrocyte A164 165) The activity of phosphofructokinase in erythrocytes is inhibited by: a) ADP b) ATP c) AMP d) citrate e) fructose 2,6-bisphosphate A165 A163 C← A164 A ← A165 B ← 166) The speed of hepatic glycolysis is different from that in skeletal muscle in that it: a) increases when cAMP increases b) decreases when ATP increases c) is regulated by insulin d) depends on the ratio NADH/NAD e) increases when AMP increases A166 167) The regulation of pyruvate kinase activity in liver is different from that in skeletal muscle because in the former it is: a) activated by fructose 1,6 bisphosphate b) allosterically inhibited by ATP c) inhibited by protein kinase A d) retro-inhibited by its product e) activated by acetyl CoA A167 168) Lactate liberated to the blood is metabolized preferentially by cardiac tissue because: a) it is easily metabolizable in high energy demands condition b) heart cells have a membrane transporter for lactate c) it protects cardiac cells against the pH change due to lactate d) it represents glucose saving for the cell e) this is favored by the kinetic characteristics of the enzyme LDH-1 (H4) A168 A166 C← A167 C ← A168 E ← 169) Glycolysis and gluconeogenesis have in common that: a) require input of reduced coenzymes b) their speed depends mainly on substrate availability c) they are exergonic processes d) they are inhibited by their respective products A169 170) Which of the following glycolytic reactions is inhibited in the liver through phosphorylation by protein kinase A? a) glucokinase b) pyruvate kinase c) phosphofructokinase d) lactate dehydrogenase e) glyceraldehyde 3 p dehydrogenase A170 171) Muscular glycolysis accelerates following the increase in intracellular concentration of: a) NADH +H+ b) glucose c) AMP d) oxygen e) H+ A171 Glycogen metabolism is regulated in slightly different ways in muscle and liver. In each of these tissues glycogen fulfills different functions. When you study, be sure to notice the way glycogen phosphorylase and glycogen synthase are regulated in each of these tissues. A169 C ← Within the cell reactions that require energy are coupled to those that supply it. Therefore, processes will only happen if the net result is energy liberation. A170 B← A171 C ← 172) Glycogen synthase catalyzes the: a) transference of glucose from UDP-glucose to a glycogen chain residue b) joining of free glucose residues to UDP c) joining of free glucose molecules to a glycogen chain residue d) formation of UDP-glucose + PPi e) branching of the glycogen chain with alfa 1-6 bonds A172 173) Hepatic glycogen phosphorylase, as opposed to that in muscle: a) is phosphorylated by a phosphorylase kinase b) is activated when it is phosphorylated c) is inhibited by glucose d) attaches Pi as such and not from ATP to form glucose-1-P e) is active when the intracellular concentration of cAMP increases A173 174) The increase in calcium ion concentration that stimulates glycogenolysis in muscle is due to: a) increase in AMP concentration b) membrane depolarization c) stimulation of alfa adrenergic receptors d) stimulation of beta adrenergic receptors A174 A172 A← A173 C ← A174 B ← 175) The increase in calcium ion concentration that stimulates glycogenolysis in liver is due to: a) increase in AMP concentration b) the response to membrane depolarization c) stimulation of beta adrenergic receptors d) stimulation of alfa adrenergic receptors A175 176) AMP can stimulate glycogenolysis in muscle because it: a) activates AMP kinase b) it is a signal of decrease in ATP concentration c) stimulates glycogen phosphorylase b activity d) promotes the entry of calcium ions to the cells A176 177) An increase in glycaemia favors glycogen synthesis in liver independently of insulin because glucose: a) enters hepatic cells in exchange for calcium ions that inactivate the calcium/calmodulin-dependent protein kinases b) activates phosphodiesterase diminishing cAMP levels c) can activate protein phosphatase 1 d) activates allosterically glycogen synthase e) increases the activity of glucokinase thus providing substrate to glycogen synthase A177 A175 D← A176 C ← A177 C ← 178) In the liver the reducing equivalents for synthesis of glucose are provided fundamentally by: a) oxidation of ketone bodies b) oxidation of pyruvate by pyruvate dehydrogenase c) β-oxidation d) glycolysis e) oxidation of glutamate A178 179) In kidney the reducing equivalents for synthesis of glucose are provided fundamentally by: a) oxidation of ketone bodies b) oxidation of pyruvate by pyruvate dehydrogenase c) β-oxidation d) glycolysis e) oxidation of glutamate A179 180) Kidney and liver gluconeogenesis have in common that they: a) depend on the input of NADH from β-oxidation b) are linked to excretion of amino nitrogen c) are regulated by pyruvate carboxylase d) are stimulated by glucagon e) stimulated by adrenalin A180 A178 C← A179 E ← A180 B ← 181) Malate dehydrogenase activity in mitochondria and cytosol is important for gluconeogenesis because this: a) allows the transport of reducing equivalents out of mitochondria b) allows the utilization of amino acids’ carbon atoms c) allows the exit of oxaloacetate formed inside mitochondria d) impedes oxaloacetate to be used for citrate synthesis e) all of the above A181 182) Pyruvate dehydrogenase and pyruvate carboxylase have as a common feature that they are regulated by: a) phosphorylation/dephosphorylation b) the concentration of pyruvate c) the concentration of acetyl CoA d) the ratio ATP/ADP e) the ratio NADH/NAD A182 183) The activity of the enzyme pyruvate carboxylase can be allosterically modified by: a) pyruvate b) ATP c) citrate d) acetyl-CoA e) oxaloacetate A183 A181 E← A182 C ← A183 D ← 184) Fructose 2,6-bisphosphate: a) is synthesized by the bifunctional enzyme b) is degraded by the bifunctional enzyme c) stimulates the activity of phosphofructokinase 1 d) inhibits the activity of fructose 1,6 bisphosphate phosphatase e) all of the above A184 185) Gluconeogenesis from pyruvate is favored by high concentrations of: a) citrate b) malonyl-CoA c) acetyl-CoA d) NAD+ e) fructose 2,6-bisphosphate A185 186) The activity of the enzyme pyruvate carboxylase can be modified allosterically by: a) pyruvate b) ATP c) isocitrate d) oxaloacetate e) acetyl-CoA A186 A184 D← A185 C ← A186 E ← 187) Lactate dehydrogenase is an enzyme that may exist in five different forms (isoenzymes), that are different in: a) KM b) regulation c) mechanism of action d) subcellular location e) all of the above A187 188) In human gluconeogenesis cannot be performed from acetyl CoA because: a) thermodynamically it is too unfavorable b) the reaction catalized by pyruvate dehydrogenase is irreversible c) it is not possible to convert a hydrophobic compound into a hydrophilic one d) the oxaloacetate formed in the Krebs cycle does not contain net carbon atoms from acetyl CoA e) glucose is a more oxidized molecule than fatty acids A188 189) A deficiency of glucose 6P dehydrogenase in erythrocytes can affect the linking of oxygen to Hb because: a) it decreases the formation of ATP b) it decreases CO2 formation, preventing the Bohr effect c) glycolysis is predominant and this increases 2,3 diphosphoglycerate formation d) it decreases the capacity to keep the Hb iron in its reduced state e) it alters the structure of membrane proteins with hemolysis A189 A187 A← A188 B ← A189 D ← 190) Referring to the oxidative phase of the pentose phosphate pathway it is correct to assert that: a) for every mol of glucose oxidized two moles of ATPs are consumed b) ribose -5-P is oxidized to CO2 and H2O c) all its reactions are reversible d) for every mol of pentose completely oxidized 2 moles of ATP are formed e) it produces NADPH + CO2 + ribose-5P A190 191) Substrate cycles of futile cycles: a) only happen in catabolic pathways b) constitute a useless expenditure of energy c) decrease the minimum flow of a metabolic pathway d) decrease the speed of a metabolic pathway e) contribute to keep a constant concentration of ATP inside the cell A191 192) During a fast gluconeogenesis is stimulated because: a) it is necessary that glucose be available to tissues that depend on it b) the effect of glucagon predominates over that of insulin c) the input of fatty acids to the liver increases d) the input of amino acids to the liver increases e) all of the above A192 A190 E← A191 C ← A192 B ← 193) What is the advantage of increasing gluconeogenesis during a fast? a) to guarantee glucose availability to tissues depending on it b) to allow the use of energy liberated by fat oxidation c) to allow the use of amino acids carbon atoms liberated from muscle d) all of the above A193 Bear in mind that an ‘advantage’ for the cell or organism is one thing and the biochemical reason for the phenomenon is another matter. Metabolism of Lipids 194) Only a very small proportion of fatty acids is actually free in the body. The immense majority of t

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