Amino Acid Structure Quiz

118 Questions

Which of the following applies to the structure of the isoleucine side chain?

Contains a branched hydrocarbon chain

Which of the following amino acids has the basic properties?

Histidine

Stereoisomers exist for all amino acids, except: Glycine

True

The primary structure of the protein is the ______ in a protein.

linear sequence of amino acids joined by peptide bonds

What type of bond is formed between the non-protein and protein part in the phosphoprotein molecule?

Phosphoester

Match the amino acid with its prevalence in the structure of collagen:

Alanine = No Serine = No Lysine = No Glycine = Yes

What is the isoelectric point?

the pH at which the net charge of the protein is neutral

Choose the reaction of pentose phosphate pathway that is accompanied by dehydrogenation and decarboxylation:

6-phosphogluconate → ribulose-5-phosphate

Choose the reactions of glycolysis that are accompanied by isomerization:

glucose-6-phosphate → fructose-6-phosphate

Choose the correct sequence of the enzymes of pyruvate dehydrogenase complex:

dihydrolipoyl transacetylase

Choose the correct sequence of the coenzymes of multienzyme complex performing oxidative decarboxylation of pyruvate:

NAD+

Choose the correct sequence of citrate cycle stages:

substrate-level phosphorylation at a level of succinyl-CoA

Choose the correct sequence of dehydrogenase reactions in Krebs cycle:

isocitrate dehydrogenation

Choose the possible causes of hyperenzymemia:

Increased number of cells producing the enzyme (tumor)

Hypoenzymemia may be due to:

Congenital enzyme deficiency

Choose the correct answers about parietal digestion of carbohydrates:

Lactose is broken down to glucose and galactose

During anaerobic glycolysis ATP is synthesized by the mechanism of substrate-level phosphorylation.

True

Synthesis of glucose from other organic non-carbohydrate compounds is called ________.

Gluconeogenesis

What is the biological role of the non-oxidative phase of the pentose phosphate pathway?

Provides ribose-5-phosphate

Choose the factors necessary for the elongation of translation:

GTP

Choose the factors necessary for the termination of translation:

codons UAA, UGA or UAG

Choose processes that require GTP energy during translation:

attaching aminoacyl-tRNA to the aminoacyl center

MRNA is involved in the processes of:

transcription

TRNA is involved in the processes of:

translation

Choose main metabolic effect of insulin:

lowers the blood glucose level

Which hormone binds to nuclear receptors?

Thyroxine

Identify the correct sequence of events in the cascade mechanism of hormonal signal transduction:

the formation of second messenger

Waxes are composed of:

Esters of an alcohol and fatty acid

Simple lipids include:

Triacylglycerols

Palmitic acid is a:

Saturated fatty acid containing 16 carbon atoms

Cholesterol belongs to which classification of lipids?

Unsaponifiable lipids

What are common structural components for mono-, di- and triacylglycerols?

Residues of trihydric alcohol glycerol and fatty acids

Which of the following are amphipathic lipids?

Phospholipids and free cholesterol

What region of phospholipid molecules is hydrophobic?

Fatty acid residues attached to the alcohol

Why are triacylglycerols completely insoluble in water?

They do not include groups capable of dissociation or having polarity

The diagnosis confirmation was provided by the finding of high blood level of:

Cortisol

All these effects are characteristic of insulin, except:

It interacts with nuclear receptors

All statements regarding insulin are true, except:

Increases lipolysis in adipose tissue

Insulin is necessary for transport of glucose to the following pair of tissues:

Adipose tissue and skeletal muscle

Binding of insulin to its receptor results in stimulation of enzyme activity, except for:

Glycogen phosphorylase

Diabetes is characterized by all of the following metabolic changes, except:

Stimulation of lipogenesis

Glucocorticoids have a catabolic effect on:

Skeletal muscle

All the following compounds are produced in the liver, except:

Chylomicrons

One of the main functions of the liver is to maintain blood glucose level. Even with the complete exclusion of carbohydrates from the diet, glucose blood level is maintained mainly due to:

Gluconeogenesis

Unconjugated bilirubin in blood is transferred bound to albumin because:

It is poorly soluble in water

Feces normally contain:

Stercobilin

Obstructive jaundice is accompanied by increasing blood level of:

Direct bilirubin

Hemolytic jaundice is accompanied by:

Stercobilin increase in urine

Decreased antitoxic function of the liver is accompanied by the following changes in the blood:

Increasing indirect bilirubin

This reaction is used in the processes of: a) oxidative deamination b) indirect deamination of amino acids c) citric acid cycle d) ornithine cycle

a, c

Choose the enzymes involved in the oxidative deamination of amino acids in the human body: a) oxidases of D-amino acids b) glutamate dehydrogenase c) α-ketoglutarate dehydrogenase d) glutamine synthetase

a, c

Choose ketogenic amino acids: a) Gly b) Lys c) Leu d) Ala

a, c

Choose possible ways to use nitrogen-free products of the transamination and deamination reactions: a) the synthesis of new amino acids b) use as an energy source c) conversion to glucose d) conversion to nucleotides

a, c, d

Amino acids are the main substrates for gluconeogenesis in fasting. Choose the amino acid metabolites that can be used for the synthesis of glucose: a) pyruvate b) HMG-CoA c) acetoacetyl-CoA d) oxaloacetate

b, d

After a meal, amino acids are the primary energy producing substrates for hepatocytes. Choose the pathways which allow to use ALA as an energy source during this period: a) synthesis of ketone bodies b) transamination c) oxidative decarboxylation of pyruvate d) TCA cycle

b, c, d

Choose the correct answer. Hydrochloric acid in the stomach: a) cause denaturation of proteins b) has a bactericidal effect c) stimulates lipase d) cause activation of pepsinogen

a, c, d

Choose exopeptidases: a) carboxypeptidases A and B b) aminopeptidase c) trypsin d) elastase

a, c

Choose the coenzyme of transaminases:

Pyridoxal phosphate

Choose an enzyme involved in the neutralization of biogenic amines:

Oxidase

Choose the compound that is formed from aspartate in the transamination reaction:

Oxaloacetate

Histamine is formed in the process of:

Decarboxylation of His

Choose the function of GABA:

Inhibitory transmitter in the central nervous system

From these statements, choose the one that characterizes the serotonin:

It is a transmitter in the central nervous system

Choose the correct ending of the sentence. Aminotransferases:

Use pyridoxal phosphate as a coenzyme

Which vitamin is a part of coenzyme that is used by amino acid decarboxylases?

Pyridoxine

Catecholamines are synthesized from:

Tyrosine

What disease is caused by the deficiency of phenylalanine hydroxylase?

Phenylketonuria

Melanin is synthesized from:

Tyrosine

Which enzyme catalyzes the following reaction: Pyruvate + Glutamate ↔ Alanine + α-Ketoglutarate

Alanine aminotransferase

Match the missing component to the ornithine cycle reaction:

? = arginine

Select the appropriate enzyme for the ornithine cycle reaction: citrulline + aspartate → argininosuccinate

argininosuccinate synthetase

The final product of detoxification of ammonia in the liver is:

urea

Select the cause of elevated level of urea in blood:

renal failure

Choose the amino acid that participates in the formation of disulfide bonds:

cysteine

Choose the amino acid that is a precursor of catecholamines:

tyrosine

Select the altered chemical reaction in patients with alcaptonuria:

homogentisate → fumarylacetoacetate

Choose the enzyme that catalyzes the reaction Glu + NH3 + ATP → Gln +ADP + H3PO4:

glutamine synthetase

Choose the correct statement:

carbamoylphosphate synthetase I neutralizes ammonia in the liver

Select the pathology associated with DOPA decarboxylase deficiency:

Parkinson's disease

What transformations occur during post-transcriptional mRNA processing? Match each process to its description:

a, b = splicing, capping, polyadenylation b, d = repression, emulsification a, c = splicing, polyadenylation

The diagnosis confirmation was provided by the finding of high blood level of:

Cortisol

All these effects are characteristic of insulin, except:

It interacts with nuclear receptors

All statements regarding insulin are true, except:

Increases lipolysis in adipose tissue

Insulin is necessary for transport of glucose to the following pair of tissues:

Adipose tissue and skeletal muscle

Binding of insulin to its receptor results in stimulation of enzyme activity, except for:

Glycogen phosphorylase

Diabetes is characterized by all of the following metabolic changes, except:

Stimulation of lipogenesis

Glucocorticoids have a catabolic effect on:

Skeletal muscle

All the following compounds are produced in the liver, except:

Chylomicrons

One of the main functions of the liver is to maintain blood glucose level. Even with the complete exclusion of carbohydrates from the diet, glucose blood level is maintained mainly due to:

Gluconeogenesis

Unconjugated bilirubin in blood is transferred bound to albumin because:

It is poorly soluble in water

Indirect bilirubin is produced in:

Macrophages

Ethanol oxidation has the following characteristics:

Occurs mostly in the liver

Obstructive jaundice is accompanied by increasing blood level of:

Direct bilirubin

Hemolytic jaundice is accompanied by:

Stercobilin increase in urine

Hepatic jaundice is accompanied by:

Appearing of urobilin in urine

Hageman factor:

Is a serine protease

Initiation complex of extrinsic pathway of coagulation contains:

Сa2+

Tenase complex contains:

Factor VIIIa

Choose the correct statements about role of calcium ions (factor IV) in blood coagulation:

Activate some plasma clotting factors

Antithrombin III:

Is a natural primary anticoagulant

The anticoagulant activity of heparin is based on:

Its ability to activate antithrombin III

Choose the plasminogen activators:

Protein С (S)

Protein C:

Hydrolyses factor Va

Factor Xa:

Is a vitamin K-dependent protein

Factor XIII:

Is a transpeptid

Vitamin K takes part in the synthesis of γ-carboxyglutamate in:

Factor Х

Plasma proteins have all these functions, except:

False

Albumins perform all of the following functions, except:

False

Haptoglobin - is:

True

Paraproteinemia - is:

True

The reduced content of haptoglobin in blood results in:

True

Choose the correct statements regarding the formation of ketone bodies:

Ketone bodies are synthesized from acetyl-CoA

In diabetes, ketosis could develop due to the following reasons:

Oxaloacetate deficiency and decreased utilization of acetyl-CoA in Krebs cycle

For ketone bodies utilization, the following conditions are required:

Sufficient level of oxaloacetate in cells to ensure the functioning Krebs cycle

Choose the correct statements regarding the ketone bodies:

Ketosis develops when 'insulin/glucagon' ratio in blood decreases

Liberation of arachidonic acid from membrane phospholipids catalyzed by phospholipase A2 is inhibited by:

Glucocorticoids

Anti-inflammatory activity of aspirin is based on inhibition of:

Cyclooxygenase

Key enzyme in leukotriene synthesis is:

Lipoxygenase

Study Notes

Amino Acid Structure

Isoleucine side chain contains a branched hydrocarbon chain
Phenylalanine side chain contains an aromatic ring
Methionine side chain contains a sulfomethyl group
Histidine has basic properties
Glycine is the only amino acid that does not have stereo-isomers
Lysine, arginine, and histidine have no charge in a weakly alkaline medium
All hydrophobic amino acids except lysine have no charge

Protein Structure

Primary structure: linear sequence of amino acids joined by peptide bonds
Primary structure is stabilized by peptide bonds
Basis of the protein primary structure is the polypeptide chain
Tertiary structure: arrangement of the entire polypeptide chain in space
Factors that form the protein tertiary structure: water environment, hydrophobic interactions, and ionic bonds
Quaternary structure: location of protomers and the character of bonds between them in an oligomeric protein

Protein-Ligand Interactions

Western blot analysis involves antigen-antibody interactions
Protein-ligand interactions are complementary in shape and charge
Myoglobin has a non-protein part (heme) that binds to globin via a coordination bond
In lipoproteins, hydrophobic bonds are formed between lipid and protein parts
In nucleoproteins, ionic bonds are formed between nucleic acid and protein parts

Protein Stability and Denaturation

Factors affecting protein stability: charge of the protein molecule, hydration shell, and molecular weight
Denaturation involves the destruction of non-covalent bonds, including hydrogen, ionic, and disulfide bonds
Denaturation leads to changes in protein solubility, loss of function, and changes in non-covalent bonds

Enzymes

Characteristics of enzymes: high specificity, high efficiency, and optimal pH and temperature
Factors affecting enzyme activity: substrate concentration, enzyme concentration, pH, temperature, and inhibitors
Competitive inhibitors bind to the active site, while non-competitive inhibitors bind to an allosteric site
Allosteric effectors can be activators or inhibitors, and their action can be reversed by increasing substrate concentration
Coenzymes: NAD+, NADP+, FMN, and FAD are coenzymes of oxidoreductases
Enzyme regulation: feedback inhibition, allosteric regulation, and covalent modification

Enzyme Kinetics

Michaelis-Menten constant (Km) is the substrate concentration at which the reaction rate is half-maximal
Km value indicates the enzyme's affinity for the substrate
Lineweaver-Burk graph: built in the double reciprocals of enzymatic reaction rate and substrate concentration
Types of enzyme inhibitors: competitive, non-competitive, and uncompetitive

Enzyme Classification

Oxidoreductases: catalyze oxidation-reduction reactions
Transferases: catalyze the transfer of a functional group
Hydrolases: catalyze the hydrolysis of a covalent bond
Ligases: catalyze the formation of a covalent bond
Lyases: catalyze the cleavage of a covalent bond without hydrolysis
Isomerases: catalyze the rearrangement of a molecule### Enzymes
A quaternary structure refers to the arrangement of multiple polypeptide chains (subunits) in an enzyme
Enzymes have 4 isoenzyme forms
Lactate dehydrogenase catalyzes the reaction of reversible conversion of pyruvate to lactate
Oxidoreductases, like lactate dehydrogenase, catalyze oxidation and reduction reactions
Enzymes can be used as drugs, but their use is limited by their short duration of action, high specificity, low stability, and difficulty in obtaining highly purified preparations

Enzyme Leaks

Enzyme leakage from the cell into the blood is influenced by:
- Size of enzyme molecules
- Presence of enzyme activators
- Intracellular localization of enzymes
- Enzyme life-time

Immobilized Enzymes

Advantages of immobilized enzymes over non-immobilized enzymes:
- Reusability
- Increased stability
- Directional transport (targeted delivery)

Urine Diastase

Urine diastase is:
- A diagnostic test for pancreatic diseases
- Measures amylase activity in urine
- Not a measure of starch or its cleavage products in urine

Treatment of Septic Wounds

Enzymes used in treatment of septic wounds:
- Trypsin
- Deoxyribonuclease
- Not alkaline phosphatase or amylase

Pancreatic Autolysis

Activation of trypsin and other enzymes can lead to pancreatic autolysis

Indicator Enzymes

Indicator enzymes are:
- Enzymes whose increased activity in plasma indicates pathology in internal organs and tissues
- Examples: aminotransferases, lactate dehydrogenase, creatine kinase

Aerobic Glycolysis

Reaction of aerobic glycolysis associated with oxidative phosphorylation:
- Glyceraldehyde 3-phosphate + NAD+ + H3PO4 → 1,3-Diphosphoglycerate + NADH

Gluconeogenesis

Gluconeogenesis is the synthesis of glucose from non-carbohydrate sources
Gluconeogenesis involves the reversal of glycolysis, with some modifications
Phosphofructokinase is not a gluconeogenic enzyme

Glycogenolysis

Glycogenolysis is the breakdown of glycogen to glucose
Glycogen phosphorylase cleaves α-1,4-glycosidic bonds in glycogen

Glycogen Synthesis

Glycogen synthase catalyzes the formation of α-1,4-glycosidic bonds in glycogen
The inclusion of 1 mole of glucose into glycogen requires 6 moles of high-energy compounds

Phosphofructokinase

Phosphofructokinase catalyzes the phosphorylation of fructose-6-phosphate to fructose-1,6-diphosphate

Glycolysis

Pyruvate kinase catalyzes the conversion of phosphoenolpyruvate to pyruvate
During anaerobic glycolysis, NADH is oxidized to NAD+ while reducing pyruvate to lactate
During aerobic glycolysis, NADH is oxidized to NAD+ in the electron transport chain

Glucose Transport

Insulin-dependent glucose transporters are present in:
- Adipose tissue
- Skeletal muscles

Indigestible Polysaccharides

Indigestible polysaccharides include:
- Cellulose
- Pectins
- Not glycogen or lactulose

Carbohydrate Metabolism

Stages of aerobic glucose oxidation to end products (CO2 and H2O):
- Glycolysis
- Oxidative decarboxylation of pyruvate
- Tricarboxylic acid cycle

Pentose Phosphate Pathway

The pentose phosphate pathway:
- Generates NADPH in the cytosol
- Provides ribose-5-phosphate for nucleic acid synthesis
- Involves the reduction of NADP+

Uronic Acid Pathway

The uronic acid pathway:
- Provides UDP-glucuronic acid for detoxification of xenobiotics and biosynthesis of glycosaminoglycans
- Involves the oxidation of glucose to glucuronic acid

Glucose-6-Phosphatase Deficiency

Glucose-6-phosphatase deficiency leads to:
- Von Gierke's disease
- Impaired glycogenolysis and glucose release from the liver

Blood Glucose Regulation

Insulin decreases blood glucose by:
- Stimulating glycolysis
- Inhibiting gluconeogenesis and glycogenolysis
Glucagon and epinephrine increase blood glucose by:
- Stimulating glycogenolysis and gluconeogenesis
- Inhibiting glycolysisHere are the study notes:
Lipid Metabolism*

Fatty Acid Oxidation

Electron Transport Chain: Uncoupling of tissue respiration and phosphorylation occurs due to increasing the permeability of the inner mitochondrial membrane to protons.
Inhibitors of Cytochrome c Oxidoreductase: Cyanides bind to the iron atoms of cytochromes a and a3, inhibiting tissue respiration.

Regulation of Lipid Metabolism

Regulatory Enzymes of Citric Acid Cycle: Isocitrate dehydrogenase is the regulatory enzyme of the citric acid cycle.
Inhibitor of Regulatory Enzymes: ATP is an inhibitor of regulatory enzymes of the citric acid cycle.

Lipid Structure and Classification

Triacylglycerols: Consist of a glycerol backbone and three fatty acid chains.
Phospholipids: Amphipathic molecules composed of a glycerol backbone, two fatty acid chains, and a phosphate group.
Lecithin: A type of phospholipid with a choline head group.
Sphingomyelin: A type of phospholipid with a sphingosine backbone and a choline head group.
Styrene: A type of simple lipid.
Cholesterol: A type of unsaponifiable lipid.

Lipid Digestion and Absorption

Lipases: Pancreatic lipase hydrolyzes triacylglycerols into fatty acids and glycerol.
Micelle Formation: Bile salts facilitate the formation of micelles, which are absorbed into enterocytes.

Fatty Acid Synthesis

Acetyl-CoA Carboxylase: The key enzyme in fatty acid synthesis, catalyzing the reaction of acetyl-CoA and CO2 to form malonyl-CoA.
NADPH: The coenzyme required for fatty acid synthesis.

Cholesterol Synthesis

Mevalonate: An intermediate in cholesterol synthesis.
Farnesyl Pyrophosphate: An intermediate in cholesterol synthesis, with 15 carbon atoms.

Eicosanoids

Arachidonic Acid: The precursor for eicosanoid synthesis.
Thromboxanes: Involved in platelet aggregation.

Let me know if you'd like me to clarify or expand on any of these points!

Identify the structural features of various amino acids, including isoleucine and phenylalanine.

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