Biochem Col 1 2020 PDF

BIOCHEM COL 1 COLLOQUIUM 1 2020 Nr Question and answer 1 Which one of the following amino acid side chains may be considered as hydrophobic at physiological pH of 7.4? A) Threonine B) Argi C) Aspartic acid D) Isoleucine 2 Explanation Threonine (A) has a polar side chain with a hydroxyl (-OH) group...

BIOCHEM COL 1 COLLOQUIUM 1 2020 Nr Question and answer 1 Which one of the following amino acid side chains may be considered as hydrophobic at physiological pH of 7.4? A) Threonine B) Argi C) Aspartic acid D) Isoleucine 2 Explanation Threonine (A) has a polar side chain with a hydroxyl (-OH) group that can form hydrogen bonds with water molecules, making it hydrophilic. Arginine (B) has a positively charged guanidinium group that can form ionic bonds with negatively charged groups in aqueous solutions, making it hydrophilic. Aspartic acid (C) has a negatively charged carboxylate group that can form ionic bonds with positively charged groups in aqueous solutions, making it hydrophilic. Isoleucine (D) has a nonpolar side chain composed of a branched alkyl group, which is hydrophobic and tends to avoid contact with water molecules. In one form of B-thalassemia, patients have significantly reduced • levels of B- globin transcripts. Notably, these B-globin transcripts are less than half the length of the normal B-globin mRNA. These • patients exhibit elevated levels of HbF and no detectable HbA1. Which of the following best explains the molecular reasons for • these observations? * a) b) c) d) Promoter mutations in the B-globin gene Covalent modification of the B-globin protein Improper folding of the B-globin protein Splicing alteration of the B-globin mRNA • • • B-thalassemia is a genetic disorder characterized by reduced or absent synthesis of the beta-globin chains of hemoglobin. The beta-globin chain is encoded by the HBB gene and requires proper splicing of the HBB pre-mRNA. Mutations in the HBB gene can result in aberrant splicing of the pre-mRNA, leading to truncated mRNA transcripts àreduced levels of functional betaglobin protein, and ultimately, anemia. In this particular form of B-thalassemia there is a splicing alteration of the Bglobin mRNA, leading to truncated mRNA transcripts. The elevated levels of HbF (fetal hemoglobin) and no detectable HbA1 (adult hemoglobin) is because the HBB gene is normally silenced after birth, and the alpha-globin chain is paired with the beta-globin chain to form HbA1. But in the absence of functional beta-globin protein, the HBB gene remains active, leading to increased production of HbF. 3 Aspirin and ibuprofen are inhibitors of? ** • a) 5-enol pyruvylshikimate-3-phosphatesynthase b) Dihydro folate reductase • c) Acetylcholinesterase d) Cyclooxygenase (COX) • 4 Which of the following vitamins is an integral component of • coenzyme A that allows two carbon units to enter the TCA cycle? • a) Thiamine • b) Pantothenic acid • c) Vitamin A • d) Biotin 5 Collagen chains are composed of large amounts of? * • A) Proline and alanine • B) Proline and glycine • C) Tyrosine and glycine D) Alanine and glycine Aspirin and ibuprofen are non-steroidal anti-inflammatory drugs (NSAIDs) and work by inhibiting the activity of the enzyme cyclooxygenase (COX) that plays a key role in the production of prostaglandins, which are signaling molecules that regulate inflammation, pain, and fever. There are two isoforms of COX: - COX-1, which is constitutively expressed in many tissues and plays a role in maintaining normal physiological functions - COX-2, which is induced by inflammatory stimuli, responsible for the production of prostaglandins that mediate pain, fever, and inflammation. Aspirin and ibuprofen inhibit COX by binding irreversibly or reversibly, respectively, to the active site of the enzyme à inhibiting prostaglandins production à leading to a reduction in pain, fever, and inflammation. Pantothenic acid is an integral component of coenzyme A that allows two carbon units to enter the TCA cycle. Coenzyme A (CoA) plays a critical role in pathways like the citric acid cycle and the synthesis and degradation of fatty acids. Pantothenic acid (vit B5), an essential nutrient required for the synthesis of CoA. In the TCA cycle, acetyl-CoA is the starting substrate and is oxidized to produce energy. Pantothenic acid is required for the conversion of pyruvate to acetyl-CoA (catalyzed by the enzyme pyruvate dehydrogenase) à is dependent on pantothenic acid (vit B5), thiamine (vit B1) and riboflavin (vit B2). Collagen, a fibrous protein that is an important component of connective tissue; skin, tendons, ligaments, and cartilage. The primary structure of collagen consists of three polypeptide chains coiled together in a triple helix. Each chain composed of a repeated sequence of amino acids, with glycine being the most common amino acid residue and proline, the lather being particularly important for stabilizing the triple helix structure of collagen. 6 Mammalian chromosomes have specialized structures with highly repetitive DNA at their ends (telomeres). Which of the following aspects of telomeric DNA replication are different from that of other chromosomal regions? a) A special DNA polymerase called telomerase can reverse the direction of replication at DNA termini. b) DNA polymerase has a special activity that cross-links DNA ends c) A special DNA polymerase called telomerase contains a template RNA- primer d) DNA polymerase contain a unique telomeric oligonucleotide used on chromosome ends • • Telomeres are specialized structures found at the ends of chromosomes consisting of repetitive DNA sequences that protect the coding regions of chromosomes from degradation and rearrangement. During DNA replication, the 3' ends of DNA molecules cannot be completely replicated by DNA polymerases à after each cell division telomeres shorten à For protection à telomerase, specialized DNA polymerase containing RNA template for extending the 3' end of the chromosome serves as a primer for DNA synthesis, allowing telomerase to add new telomeric repeats to the end of the chromosome. - Option A is incorrect because telomerase does not reverse the direction of replication at DNA termini. Instead, it adds new DNA nucleotides to the 3' end of the DNA molecule. - Option B is incorrect because DNA polymerase does not cross-link DNA ends. Rather, it catalyzes the formation of phosphodiester bonds between adjacent nucleotides in the growing DNA strand. - Option D is incorrect because there is no unique telomeric oligonucleotide used on chromosome ends. The sequence of telomeric repeats varies between species and can be composed of different numbers and arrangements of nucleotides. 7 The aldehyde and ketone moieties of the carbohydrate with 5 and 6 carbons will spontaneously react with alcohol groups present in neighboring carbons to produce ring structures. The rings can open and close allowing for different configurations of the atoms in the ring. Which of the following represents the carbon, where this rotation occurs? a) Anomeric b) Hydroxy c) Glycosidic d) Chiral 8 Which of the following describes a common theme in the structure of DNA binding proteins? a) The presence of a specific helix that lies across the major groove of DNA b) The ability to form multiple hydrogen bonds between the protein peptide backbone and the DNA phosphodiester backbone c) Ability to form dimers with disulfide linkage d) The presence of zinc Option A, the anomeric carbon is the carbon atom that undergoes rotation during the ring-opening and closing process. Option B, hydroxy, refers to the hydroxyl groups that can react with the aldehyde or ketone group to form the cyclic structure. Option C, glycosidic, refers to the bond formed between two sugar molecules through the reaction between the anomeric carbon of one sugar and the hydroxyl group of another sugar. Option D, chiral, a carbon atom that is bonded to four different chemical groups àtwo possible configurations (R and S) that are mirror images of each other. Most carbon atoms in sugars are chiral, Option A is correct; Many DNA binding proteins contain a common structural motif; helix-turn-helix (HTH), which is involved in the recognition and binding of specific DNA sequences. HTH motif consists of two alpha helices connected by a short turn, with one helix lying across the major groove of the DNA, allowing for specific interactions with the DNA bases. Option B is incorrect because DNA binding proteins generally form hydrogen bonds with the nitrogenous bases of DNA, not the phosphodiester backbone. Option C is incorrect because not all DNA binding proteins form dimers, and disulfide linkages are not a common mode of dimerization for DNA binding proteins. Option D is incorrect because while some DNA binding proteins do contain zinc ions in their structures, this is not a universal feature of all DNA binding proteins, and it is not a defining characteristic of the DNA binding mechanism. 9 The function of many enzymes, membrane transporters and other proteins can be quickly activated or deactivated by phosphorylation of specific amino acid residues catalyzed by enzymes called: • a) Cyclases b) Phosphatases c) Proteases • D) Kinases; enzymes responsible for phosphorylating specific amino acid residues in proteins. - This phosphorylation can activate or deactivate the function of enzymes, membrane transporters, and other proteins. - Phosphorylation is a common mechanism for regulating cellular signaling pathways and controlling various cellular processes such as metabolism, growth, and differentiation. On the other hand, phosphatases are responsible for removing the phosphate group from phosphorylated amino acid residues, thus reversing the effects of kinases and restoring the original state of the protein. d) Kinases 10 A patient was diagnosed with a deficiency of the lysosomal enzyme a- glycosidase. The name of the deficient enzyme suggests that it hydrolyzes glycosidic bond, which is a bond formed? * a) Internally between the anomeric carbon of a monosaccharide and its own 5th hydroxyl group b) Between the anomeric carbon of a sugar and an oxygen or nitrogen of another molecule c) Through multiple hydrogen bonds between two sugar molecules d) Between two anomeric carbons in polysaccharides B) The name of the deficient enzyme "a-glycosidase" suggests that it hydrolyzes a glycosidic bond wich are covalent bonds that link a sugar molecule to another molecule, such as another sugar or nitrogen or oxygen. They are formed between the anomeric carbon of a sugar molecule (the carbon that is involved in ring closure) and the oxygen or nitrogen of another molecule. Hydrolysis of a glycosidic bond involves breaking this covalent bond with the addition of a water molecule, which can be catalyzed by enzymes like aglycosidase. Lysosomal enzymes like a-glycosidase are involved in the breakdown glycoproteins and glycolipids, which require the hydrolysis of glycosidic bonds to release their constituent monosaccharides. 11 Synthetases are enzymes which catalyze: a) isomerization reactions b) Joining of two substrates, using ATP c) Lysis, forming a double bond d) Group transfer reactions • • This process is known as ligation and results in the formation of a new covalent bond between the two substrates. Synthetases are typically named after the substrates they ligate, for example ATP synthetases, which join ADP and Pi to form ATP. A) isomerases; catalyze the rearrangement of atoms within a molecule to form an isomer. C) Lysis involves the cleavage of a covalent bond to form two or more smaller molecules, which is typically catalyzed by lyases. D) Group transfer reactions involve the transfer of a functional group from one molecule to another, catalyzed by transferases. 12 During the normal processes of the cell cycle, specific types of DNA - protein complexes form and dissociate which allow condensation and decondensation of the chromosomes. Which of the following is the major attractive force between the DNA and the proteins, allowing these complexes to form? a) Electro static interactions b) Vander Waals forces c) Hydrophobic interactions d) Disulfide linkages A) The major attractive force between DNA and proteins that allows the formation of specific types of DNA-protein complexes during the normal processes of the cell cycle is electrostatic interactions. These interactions involve the attraction between positively charged amino acid residues on the proteins, such as lysine and arginine, and the negatively charged phosphate groups on the DNA backbone. The formation of electrostatic interactions between DNA and proteins is important for the compaction of DNA into chromatin during the cell cycle, which allows the chromosomes to be efficiently segregated during cell division. Vander Waals forces and hydrophobic interactions are also important in proteinDNA interactions but to a lesser extent. Disulfide linkages involve the covalent bonding of two cysteine residues through a sulfur-sulfur bond and are not typically involved in protein-DNA interactions. 13 Which of the following sentences concerning vitamin A is correct? a) Retinol is transported to the liver by the plasma retinolbinding-protein A) Retinol is transported to the liver by the plasma retinol-binding protein (RBP). This is correct also but it has to be processed by the intestinal mucosa. B) B-carotene is cleaved in the intestinal mucosa by beta-carotene dioxygenase, yielding retinal. b) B-carotene is cleaved in the intestinal mucosa by carotene dioxygenase, yielding retinal c) Retinal is a gene regulator d) Retinoic acid is the prosthetic group of the rhodopsin’s C) Retinal is a form of vitamin A that is involved in vision. While it is true that retinoids, including retinal, can act as gene regulators, it is not a primary function of vitamin A. D) Retinoic acid is a metabolite of vitamin A that is involved in gene expression and is not the prosthetic group of the rhodopsin’s. The prosthetic group of rhodopsin is retinal, which is derived from vitamin A. 14 Protein kinases phosphorylate proteins only at certain hydroxyl groups on amino acid side chains. Which of the following groups of amino acids all contain side chain hydroxyl groups? a) b) c) d) Lysine, Arginine, Proline Aspartate, tathamate, serine Serine, threonine, tyrosine Threonine, phenylalanine, arginine 15 Clinitest is a copper reduction method of detecting reducing sugars. Which one of the following sugars cannot be detected with clinitest: a) b) c) d) Galactose Fructose Lactose Sucrose 16 A cytosolic protein has a helical structure. The non-polar amino acids form cluster: a) b) c) d) The interior and surface of the protein Non-polar aminoacid cannot form helical structures The surface of the protein In the interior of the protein 17 Which post-translational protein modification is reversible, rapid and affects Ser, Thr, Tyr. (Serine, threonine tyrosine) ** A) Hydroxylation B) N-glycosylation C) Phosphorylation D) Gamma-carboxylation Proteins have parts that are polar or non-polar. In a helical protein, the non-polar parts are usually grouped together in the middle of the protein, away from the watery environment outside. The polar parts are on the outside, where they can interact with water and other molecules. Phosphorylation is the process of adding a phosphate group to a protein molecule. This modification can occur on the side chains of serine, threonine, and tyrosine residues. Phosphorylation is a reversible modification, and it is rapidly regulated by the activity of enzymes called protein kinases and protein phosphatases, which add or remove phosphate groups, respectively. 18 A 48-year man presents to the emergency department with acute abdominal pain. Serum amylase and lipase activity were significantly elevated, but the bilirubin concentration was within the reference range. Which of the following disease explains the information provided? ** a) b) c) d) Prostate cancer Kidney cancer Acute pancreatitis Viral hepatitis 19 Mothers taking warfarin for anticoagulation during pregnancy may have children with fetal warfarin syndrome involving very short nose and skeletal changes. Studies of the action of the anticoagulants dicumarol and warfarin (The latter also a hemorrhagic rat poison) - have revealed which of the following? a) Vitamin K is a clotting factor b) The action of vitamin E is antagonized by these compounds c) Vitamin K is essential for gamma-carboxylation of glutamate d) Vitamin C is necessary for the synthesis of fibrinogen 20 Sigmoidal enzyme kinetics are common for: a) b) c) d) Elevated serum amylase and lipase levels are characteristic laboratory findings in acute pancreatitis. On the other hand: Prostate cancer (option A), kidney cancer (option B), and viral hepatitis (option D) are unlikely to cause acute abdominal pain and elevated amylase and lipase levels. All enzymes Enzymes inhibited by a competitive inhibitiors Multimeric enzymes No enzymes Warfarin is an anticoagulant drug à inhibits vitamin K-dependent enzyme àinhibits gamma-carboxylation of glutamate residues on clotting factors II, VII, IX, and X (crucial for the activation of these clotting factors and their binding to calcium)à necessary for blood coagulation. Vitamin E (option B) is not directly affected by warfarin, as it is not involved in blood coagulation. Vitamin C (option D) is not necessary for the synthesis of fibrinogen, even if it does play a role in collagen synthesis and other connective tissue proteins. Vitamin K (option A) is not a clotting factor itself, but it plays a critical role in the coagulation cascade à enabling the gamma-carboxylation of specific amino acid residues on clotting factor Multimeric enzymes are composed of two or more subunits that can interact with each other, leading to cooperative binding of substrates and/or allosteric modulators. This cooperative behavior can result in sigmoidal enzyme kinetics, which means that the reaction rate initially increases slowly, then accelerates rapidly, and finally levels off at a maximum rate. Examples; hemoglobin, which binds oxygen cooperatively, and aspartate transcarbamoylase, which is regulated by allosteric interactions between its catalytic and regulatory subunits. 21 Which of the following best describes the characteristics of polar amino acids? • a) Positively charged - b) More likely to be exposed to water than to be found in the interior of a folded protein c) Partially charged due to the oxygen atom in their carboxyl group d) Ionizable in water Polar amino acids have a polar side chain, which makes them hydrophilic (water-loving). they are more likely to be exposed to water than to be found in the interior of a folded protein. This property is important for the solubility and stability of proteins. Option A is incorrect because positively charged amino acids (such as lysine and arginine) are called basic amino acids, not polar amino acids. Option C is partially correct, but not a complete description. Polar amino acids do contain a carboxyl group (-COOH) which can make them partially charged due to the electronegative oxygen atom in the group. However, not all polar amino acids contain a carboxyl group (such as serine and threonine) and not all carboxyl groups in amino acids are partially charged. Option D is also partially correct, but not a complete description. Polar amino acids can be ionizable in water because of their polar side chains or carboxyl groups. However, not all polar amino acids are ionizable, and there are other amino acids that can be ionizable in water, such as acidic and basic amino acids. 22 Hemoglobin and myoglobin are proteins composed primarily of which of the following types of secondary structures? * a) Disulfide bond b) Alpha helix c) Triple helix d) Beta-pleated sheet • • • Alpha helix is a common secondary structure in proteins, formed by the twisting of a polypeptide chain into a right-handed coil. Hemoglobin and myoglobin are both heme-containing proteins that play important roles in oxygen transport and storage in the body. The alpha helices in these proteins are arranged in a compact globular structure, with the heme group bound to a histidine residue in the protein. 23 An infant present with growth retardation, weak muscle tone and lethargy. He is diagnosed with pyruvate carboxylase deficiency. Which of the following vitamins is required as a coenzyme for its action? ** a) Lipoicacid b) Riboflavin c) Niacin d) Biotin (VIT B7) HARPERS: Gluconeogenesis & Control of the Blood Glucose; chptr 19; p 153: A. PYRUVATE & PHOSPHOENOLPYRUVATE: Mitochondrial pyruvate carboxylase catalyzes the carboxylation of pyruvate to oxaloacetate, an ATP-requiring reaction in which the vitamin biotin is the coenzyme. Biotin binds CO2 from bicarbonate as carboxybiotin prior to the addition of the CO2 to pyruvate. • • • 24 Which of the following sentences Wilson disease is correct? * a) In this condition copper is absorbed by gastrointestinal tract, but cannot be transported to blood b) The condition is treated with chelation medications to bind body copper and increase its urinary excretion c) It is caused by the mutation in the gene for ATP7A protein Pyruvate carboxylase, an enzyme with crucial role in gluconeogenesis. Pyruvate carboxylase deficiency impairs gluconeogenesis, leading to a decrease in glucose production. Biotin (vit B7), coenzyme required for the action of pyruvate carboxylase, serves as a covalently-bound prosthetic group that is essential for the enzymatic activity of the protein. Wilson's disease is a rare genetic disorder that causes copper to accumulate in the body, including the liver, brain, and eyes. Copper is absorbed by the gastrointestinal tract but cannot be transported to the blood leading to accumulation of copper in the liver, which can cause liver damage and other complications. The disease is caused by mutations in the ATP7B gene, which encodes a coppertransporting ATPase that has a role in the excretion of copper from the liver into the bile. Treatmen; d) During the disease the excretion of excess copper in the urine is blocked Lab manual page; 8. 25 Choose the incorrect feature of human genetic code: a) Overlapping b) Not punctuated Harpers Illustrated Biochemistry; THE GENETIC CODE IS DEGENERATE, UNAMBIGUOUS, NONOVERLAPPING, WITHOUT PUNCTUATION, & UNIVERSAL • The genetic code is punctuated, meaning that it is read in three-letter sequences called codons. Each codon corresponds to a specific amino acid or a stop signal. PROTEIN SYNTHESIS & THE GENETIC CODE p;359: - As discussed below, the reading of the genetic code during the process of protein synthesis does not involve any overlap of codons. Thus, the genetic code is nonoverlapping. Furthermore, once the reading is commenced at a specific codon, there is no punctuation between codons, and the message is read in a continuing sequence of nucleotide triplets until a translation stop codon is reached. • The code is also degenerate, meaning that multiple codons can encode the same amino acid. Additionally, the genetic code is universal, meaning that the same codons encode the same amino acids across all living organisms. The genetic code is not overlapping in humans, as each codon is read sequentially without overlap. c) Universal d) Degenerte • • 26 Enzymes are effective catalysts because they can do which of the following? * a) Catalyze reactions that otherwise would not occur b) Shift the equilibrium of reactions toward more complete conversion to product. C) Decrease the free energy of activation of reactants D) Decrease the standard free energy change (∆G0’) of reactions 27 Alpha-1-antitrypsin a) Is involved in elastin biosynthesis and formation of elastin cross-links b) Its deficiency is lethal because it is a potent inhibitor of neutrophil elastase c) Inhibits N- or C- terminal procollagen peptidases and is produced by collagen- secreting cells d) Inhibits neutrophil elastase, is produced mainly in the liver and compromises more than 90% of the alpha1-globulin fraction of normal serum Option A) is incorrect because enzymes do not catalyze reactions that would not occur at all, but rather they enhance the rate of reactions that would occur spontaneously, but too slowly to be biologically relevant. Option B) is incorrect because enzymes do not shift the equilibrium of reactions toward more complete conversion to products. Enzymes increase the rate of both the forward and reverse reactions equally, thus they do not affect the equilibrium point of the reaction. Option D) is incorrect because enzymes do not affect the standard free energy change (∆G 0) of reactions, which represents the ae in free energy between the products and reactants in their standard states. Enzymes only reduce the activation energy of the reaction. FERRIER; UNIT I: Protein Structure and Function, Fibrous Proteins; p142: - - Blood and other body fluids contain α1 -antitrypsin (AAT or A1AT), which inhibits a number of proteolytic enzymes (called proteases or proteinases) that hydrolyze and destroy proteins. AAT has the important physiologic role of inhibiting neutrophil elastase, a powerful protease that is released into the extracellular space and degrades elastin of alveolar walls as well as other structural proteins in a variety of tissues. Most of the AAT found in plasma is synthesized and secreted by the liver. AAT comprises more than 90% of the α1 -globulin fraction of normal plasma. Extrahepatic synthesis occurs in monocytes and alveolar macrophages. 28 Which one of the following statements is correct? Choose one answer: a) Beta-bends often contain proline b) The alpha-helix is stabilized primarily by ionic interactions between the side chains of amino acids c) Beta-sheets exist only in the antiparallel form d) The alpha-helix can be composed of more than one polypeptide chain FERRIER; UNIT I: Protein Structure and Function, Structure of Proteins; p: 56 β-Bends (reverse turns, β-turns): • β-Bends reverse the direction of a polypeptide chain, helping it form a compact, globular shape. They are usually found on the surface of protein molecules and often include charged residues and are stabilized by the formation of hydrogen and ionic bonds. • β-Bends are generally composed of four amino acids, one of which may be proline, the amino acid that causes a kink in the polypeptide chain. • Glycine, the amino acid with the smallest R group, is also frequently found in βbends. B) no, because the alpha-helix is primarily stabilized by hydrogen bonding between the carbonyl group of one amino acid and the amide group of another amino acid, forming a helical structure. C) no, because Beta-sheets can exist in both parallel and antiparallel forms, depending on the orientation of the neighboring strands. D) no because the alpha-helix is composed of a single polypeptide chain, and it is not typically found in multi-chain protein structures. 29 Kinases are a class of enzymes that incorporate a phosphate onto their substrates. The catalytic activity of kinases classifies them as members of which of the following enzyme families? * a) Hydrolases b) Ligases c) Isomerases d) Transferases • Kinases are enzymes that transfer a phosphate group from a donor molecule (usually ATP) to a specific amino acid residue on a substrate protein. Therefor they are classified as members of the transferase family of enzymes. - Hydrolases catalyze the cleavage of chemical bonds using water, Ligases join two molecules together. Isomerases catalyze the rearrangement of chemical bonds within a molecule. 30 Which of the following sentences concerning vitamin C is false? a) It participates in the synthesis of epinephrine b) It participates in regeneration of vitamin E c) It improves Iron absorption d) It maintains metal cofactors in their higher valence state Vitamin C can act as a reducing agent, but it does not maintain metal cofactors in their higher valence state. In fact, vitamin C can chelate metal ions and enhance their excretion from the body, which can be important in cases of metal toxicity. And its main function is to maintain metal cofactors in the lower valence state. Vitamin C, also known as ascorbic acid, has several important functions in the body, including: A. Participation in the synthesis of epinephrine and other neurotransmitters B. Regeneration of vitamin E, which is an important antioxidant C. Enhancement of iron absorption by reducing non-heme iron to a more absorbable form Lecture slide p; 48: 31 In iron deficiency anemia we observe the following? * a) Low serum iron level and low transferrin b) High serum iron level and low TIBC (total iron-binding capacity) c) Low serum iron level and low TIBC d) Low serum iron level and high TIBC 32 Which of the following substance is most prone to peroxidation Iron deficiency anemia is caused by insufficient iron in the body. The body cannot produce enough hemoglobin. Iron is an essential component of hemoglobin, and without enough iron, the body cannot make enough hemoglobin, resulting in anemia. In iron deficiency anemia, the - serum iron level is low because there is not enough iron in the body. - The TIBC (total iron-binding capacity) is high because the body is trying to increase its capacity to bind and transport iron, indicating that the body is in a state of iron deficiency. • Linoleic acid is an unsaturated fatty acid with two double bonds, which makes it highly susceptible to oxidation by reactive oxygen species, resulting in the formation of peroxides. • Aspartic, palmitic, and glutamic - acid are amino acids and do not undergo peroxidation in the same way that linoleic acid does. • Katal (kat) is a unit of measurement for enzyme activity, defined as: - The amount of enzyme that catalyzes the conversion of 1 mole of substrate per second under specified conditions (pH, temperature, etc.). a) Linoleic acid b) Aspartic acid c) Palmitic acid d) Glutamic acid 33 Katal (kat) is defined as enzyme activity which will catalyze the transformation of? * a) mol of substrate transformed per second in specified system b) Mol of substrate transformed per minute in specified system c) Micro mol of substrate transformed by second in spec system d) Micro mol of substrate transformed per minute in specified system - This means that one katal of enzyme activity is equivalent to the transformation of one mole of substrate per second in a specified system. 34 The greatest buffering capacity at physiological pH would be provided by a protein rich in which of the following amino acids? * a) Cysteine • • Histidine has a side chain with a pKa value that is close to physiological pH (around 7.4), thus in this pH histidine can act as both a proton donor and acceptor, making it an effective buffer. Histidine residues are also often found in the active sites of enzymes, where they can play important roles in catalysis. b) Histidine - c) Proline - d) Alanine 35 Which of the following vitamins becomes a major electron acceptor as a coenzyme, aiding in the oxidation of numerous substrates? a) VitaminB6 b) VitaminB1 c) Biotin d) Niacin • • • Cysteine has a thiol group in its side chain that can act as a weak acid, but its pKa is much lower than physiological pH, not effective buffer at this pH. Proline and alanine do not have any charged side chains, so they would not be able to act as buffers. Niacin (Vit B3) a component of the coenzymes NAD+ (nicotinamide adenine dinucleotide) and NADP+ (nicotinamide adenine dinucleotide phosphate) involved in oxidation-reduction reactions. Serving as electron carriers, accepting electrons from substrates being oxidized and transferring them to molecules being reduced. Process is crucial for the production of ATP in the mitochondria. ü Vitamin B1 (thiamine) is involved in the metabolism of carbohydrates. ü Vitamin B6 (pyridoxine) plays a role in amino acid metabolism. ü Biotin is involved in the metabolism of fatty acids, glucose, and certain amino acids, but it does not act as an electron acceptor. 36 Over 200 disorders with complex phenotypes derive from changes in human chromosomes. Given that the chromosome of mammalian cells may be 20 times as large as those of E-coli, how can replication of mammalian chromosomes be carried out in just a few minutes? a) Eukaryotic DNA polymerases are extraordinarily fast compared with prokaryotic polymerases. b) The higher temperature of mammalian cells allows for an exponentially higher replication rate. c) Hundreds of replication forks work simultaneously on each piece of chromosomal DNA. • • • During replication, the two DNA strands are opened by helicase at multiple sites à Multiple Replication forks are created where the two strands are separated. The replication fork then moves along the DNA strand, adding new nucleotides to each strand by DNA polymerase. Multiple replication forks allows the rapid replication of large chromosomes. ü Eukaryotic DNA polymerases are not necessarily faster than prokaryotic polymerases. ü The higher temperature of mammalian cells does not allow for a significantly higher replication rate. ü RNA polymerases are not involved in DNA replication. d) Many different RNA polymerases carry out replication simultaneously on chromosomal DNA. 37 Osteogenesis imperfecta? * a) Develops when collagen is exposed chronically to low levels of neutrophil elastase b) Is a disease caused by the production of abnormal pro-alphachains, which prevent the formation of required triple helical conformation of collagen. c) Is the result of abnormal iron of copper metabolism, and thus the low activity of prolyl or lysis oxidase d) Is a brittle bone syndrome, related to the low activity of alpha-1antitrypsin Osteogenesis imperfecta, a genetic disorder affecting the formation and quality of collagen; main protein in bone tissue. - is caused by mutations in genes that are involved in the production of collagen, most commonly COL1A1 and COL1A2. These genes encode the pro-alpha chains of type I collagen, the most abundant form of collagen in bone tissue. Mutations in these genes can result in the production of abnormal proalpha chains that prevent the formation of the required triple helical conformation of collagen. As a result, the collagen produced is weaker and more prone to fractures. 38 Choose the incorrect application of the PCR technique: • a) Detection of specific tissue proteins. b) Detection of low-abundance nucleic acid and sequencers. PCR (polymerase chain reaction) is a laboratory technique used to amplify specific segments of DNA or RNA. It is a powerful tool used in many different applications, including: ü Detection of low-abundance nucleic acid and sequencers ü Forensic analysis of DNA samples ü Prenatal diagnosis and carrier detection, for example cystic fibrosis c) Forensic analysis of DNA samples. d) Prenatal diagnosis and carrier detection, for example cystic fibrosis. • PCR is not used to detect specific tissue proteins. - Protein detection typically involves techniques such as Western blotting, ELISA, or immunohistochemistry, which rely on the specific binding of antibodies to the target protein. 39 Which of the following carbohydrate or its derivative is mostly present in a furanose form: • Ribose is a monosaccharide with five carbon atoms (furanose) is mostly present in the furanose form. a) Glucuronic acid b) D-galactose c) Ribose d) L-iduronic acid ü Glucuronic acid (option a) and L-iduronic acid (option d) are both hexuronic acids and exist in the pyranose (six carbon) form. ü D-galactose (option b) can exist in both furanose and pyranose forms, but it is more commonly found in the pyranose form. 40 Choose the tetrahydrofolate dependent reaction: a) Synthesis of glycine from serine. b) Transfer of methyl groups to vitamin B12. c) Synthesis of thymine d) All answers are correct Ferrier A) page: 723; 2. Serine: This amino acid can be converted to glycine and N 5, N 10 -methylenetetrahydrofolate (Figure 20.6A). Serine can also be converted to pyruvate by serine dehydratase (Figure 20.6B). B) page: 726; a. Resynthesis of methionine: Hcy accepts a methyl group from N5-methyl-tetra-hydrofolate (N 5 methyl-THF) in a reaction requiring methylcobalamin, a coenzyme derived from vitamin B 12 à Cobalamin is remethylated from N 5 -methyl-THF. C) page: 831; E. Synthesis of deoxythymidine monophosphate by thymidylate synthase, which uses N 5, N 10 methylene tetrahydrofolate as the source of the methyl group. Inhibitors of thymidylate synthase include thymine analogs such as 5-fluoro-uracil, which serve as antitumor agents. ü DHF can be reduced to THF by dihydrofolate reductase an enzyme that is inhibited by folate analogs such as methotrexate. ü By decreasing the supply of THF, these drugs inhibit purine synthesis, prevent methylation à decrease the availability of essential component of DNA. ü DNA synthesis is inhibited and cell growth slowed. Thus, these drugs are used to decrease the growth rate of cancer cells. LECTURE; page 95,VITAMINS 41 A teenage boy is diagnosed with Kearns-Sayre disease by demonstrating a deletion of mitochondrial DNA in tissue obtained by muscle biopsy. Unique properties of mitochondrial DNA are best summarized as which of the following? * a) Linear duplex DNA that encodes over 70 proteins of the respiratory chain and has a mutation rate 5-10 times higher than nuclear DNA b) Circular, single-stranded, compromising 1% of cellular DNA with high mutation rate c) Circular, single-stranded DNA with low mutation rate that encodes a minority of mitochondrial peptides d) Linear duplex DNA with a length similar to that of one nuclear chromosome, present as 50-100 copies per cell. Mitochondrial DNA is a: • Circular, double-stranded DNA, although circular, it is referred to as "linear duplex DNA" to indicate its double-stranded nature. • Maternally inherited and present in multiple copies in each cell. • Its length is similar to that of one nuclear chromosome • encodes for 13 proteins that are essential components of the oxidative phosphorylation system, which produces ATP in mitochondria. HARPERS; ONE PERCENT OF CELLULAR DNA IS IN MITOCHONDRIA, page 332; • Human mitochondria contain two to ten copies of a small circular doublestranded DNA molecule that makes up approximately 1% of total cellular DNA that codes for mt ribosomal and transfer RNAs and for 13 proteins that play key roles in the respiratory chain. • Although it is circular, it is referred to as "linear duplex DNA" to indicate its double-stranded nature. • mtDNA has several unique properties that distinguish it from nuclear DNA. These properties are best summarized as follows: ü Unlike nuclear DNA, which exists as two copies in each cell, mitochondrial DNA can be present in multiple copies ranging from 50 to 100 per cell, depending on the cell type. ü Mutation rate is relatively higher than that of nuclear DNA, but it is still lower than the mutation rate of single-stranded DNA. ü Mutation rate it is generally higher for mitochondrial DNA due to reactive oxygen species generated during oxidative phosphorylation and the limited DNA repair mechanisms in mitochondria. 42 A high homocysteine level could be associated with deficiency of which of the following vitamins? • a) VitaminB3 b) Vitamin C c) Vitamin B12 d) Vitamin B1 Homocysteine à amino acid produced as a byproduct of protein metabolism. Deficiencies in vit B12, B6, and folic acid lead to elevation of homocysteine due to these vitamins are involved in the metabolism of homocysteine. FERRIER; page. 1027; III. COBALAMIN (VITAMIN B12): Vitamin B 12 is required in humans for two essential enzymatic reactions: 1) The re-methylation of homocysteine (Hcy) to methionine. ü Note: Folic acid (N 5 -methyl THF) is also required in the re-methylation of Hcy). Therefore, deficiency of B 12 or folate results in elevated Hcy levels) 2) The isomerization of methyl-malonyl coenzyme A (CoA), à produced during degradation of; isoleucine, valine, threonine, methionine, and fatty acids with odd numbers of carbon atoms. • 43 Choose the correct answer: When cobalamin is deficient, unusual (branched) FAs accumulate and become incorporated into cell membranes, including those of the central nervous system (CNS). This may account for some of the neurologic manifestations of vitamin B 12 deficiency A) Restriction endonucleases recognize and cut DNA seq recognition sequences wich are palindromicà for ex; GAATTC and AAGCTT. a) A sequence that can be recognized by restriction endonucleases is ATCAGC. B) NO; A DNA sequence that is recognized by a restriction enzyme is called a restriction site or recognition sequence à cut the DNA at specific locations b) A DNA sequence that is recognized by a restriction enzyme is generating fragments with specific ends à used for DNA cloning, sequencing…. called polymerase site. On the other hand, a polymerase site refers to a DNA sequence that serves as a binding site for a DNA polymerase enzyme during DNA replication or PCR. c) Two DNA fragments from different sources cannot be cut by the same restriction endonuclease. C) restriction enzymes can cut DNA from different organisms and different regions of the same genome. d) Restriction endonucleases are bacterial enzymes that cleave the double- stranded DNA into smaller fragments at specific D) Restriction endonucleases (restriction enzymes) are bacterial enzymesà nucleotide sequence recognize and cut DNA at specific nucleotide sequences. 44 Some proteins can aggregate and form amyloid deposits. Such deposits: a) Are formed by helical proteins, because the helical structure is resistant to proteolytic action b) Are characteristics for Alzheimer's disease c) Results from the accumulation of denatured protein that have random conformations d) Are associated with the accumulation of amyloid precursor protein 45 Cleavage of procollagen molecules: a) Is catalyzed by N-and C-procollagen peptidases in the cell cytoplasm b) Is catalyzed by copper-dependent enzyme c) Is catalyzed by N- and C-procollagen peptidases in the extracellular space d) Is catalyzed by iron-dependent enzymes FERRIER; page.66; VI. PROTEIN MISFOLDING: A. Amyloid diseases • • • • • • • Misfolding of proteins may cause normal proteins to take on a unique conformational state that leads to long, fibrillar protein consisting of βpleated sheets. Accumulation of these insoluble, spontaneously aggregating proteins, called amyloids à degenerative diseases such as Parkinson and Huntington and particularly in Alzheimer disease. The dominant component of the amyloid plaque is amyloid β (Aβ), an extracellular peptide containing 40–42 amino acid residues. This peptide, when aggregated in a β-pleated sheet configuration, is neurotoxic and is the central pathogenic event leading to the cognitive impairment. Procollagen is a precursor of collagen, the most abundant protein in the extracellular matrix of connective tissues. Procollagen is secreted by cells in a triple-stranded form, which is then cleaved to form mature collagen molecules. The cleavage of procollagen is catalyzed by specific enzymes called procollagen peptidases, which cleave the N- and C-terminal pro-peptides from the procollagen molecule, allowing it to assemble into mature collagen fibrils. ü The cleavage of procollagen occurs in the extracellular space, not in the cell cytoplasm, and is not catalyzed by copper- or iron-dependent enzymes. COLLOQUIUM 1, FIRST RETAKE. * = question was on last year's colloquium 46 Drugs that inhibit enzymes in a noncompetitive manner • Non-competitive Inhibition of enzyme à inhibitor binds to not active site on enzyme. will have which of the following effects on the Michaelis • Maximum velocity (Vmax) of the enzyme reaction is reduced without affecting the Menten equation derived parameters: Vmax and or Km? * enzyme substrate (Km) affinity. • Since non-competitive inhibition does not affect Km, the value of Km remains the a) A decrease km but no effect on Vmax same. However, since non-competitive inhibition reduces the maximum velocity of the reaction, Vmax is decreased. b) Decreases both Vmax and KM c) Decrease Vmax but no change in Km d) Increase Km but no change in Vmax 47 In Schilling test low excretion with urine of radiolabeled vitamin B12 in the 1 stage and normal excretion of this vitamin in the 2´nd stage may occur in patients? ** • • The Schilling test; diagnostic test à determine pernicious anemia, caused by a deficiency in vitamin B12. Administration of a small amount of radioactive vitamin B12à teste ability to absorb B12 by measuring the amount of vitamin B12 excreted in the urine. 1. Stage 1 à patient is given non-radioactive B12 and injection of radioactive B12. If intrinsic factor production issues B12 will not be absorbed à low excretion of radiolabeled vitamin B12 in the urine. 2. Stage 2à patient is given B12 with intrinsic factor. If inability to absorb B12 is due to intrinsic factor lack, a) With problems with intrinsic factor addition of intrinsic factor will allow for normal absorption à excretion of the vitamin in the urine. production LECTURE; page 115, 116; VITAMINS b) With coeliac disease c) On vegan diet d) With malabsorpsjon 48 Which of the following amino acids are not present in protein? a) Taurine, beta-Alanine a) Proline, Valine b) Alanine, selenocystein c) Cystein, Ornithine 49 The best markers for early diagnostics of myocardial infarction are? ** a) Total creatine kinase and aspartate transaminase • • b) Creatine kinase isoenzyme MB and Cardiac troponin ü Lactate dehydrogenase (LDH), aspartate transaminase (AST), amylase, and acidic phosphatase are not specific markers for myocardial infarction and may be elevated in other conditions, such as liver or pancreatic disease. c) Lactate dehydrogenase and amylase d) acidic phosphatase and lactate dehydrogenase 50 A patient was diagnosed with a deficiency of the lysosomal enzyme a- glycosidase. The name of the deficient enzyme suggests that it hydrolyses a glycosidic bond, which is a bond formed? a) Internally between the anomeric carbon of a monosaccharide and its own 5th carbon hydroxyl group b) Between the anomeric carbon of sugar and an O or N of another molecule c) Through multiple hydrogen bonds between two sugar molecules d) Between two anomeric carbons in polysaccharides Creatine kinase (CK) and its isoenzyme CK-MB were previously used as markers for myocardial infarction, but they are less specific and sensitive than cardiac troponin. Cardiac troponin is a protein released into the bloodtam when heart muscle cells are damaged and is considered the most specific and sensitive marker for myocardial infarction. • The name of the enzyme, a-glycosidase, suggests that it hydrolyzes a glycosidic bond (bond that forms between the anomeric carbon of a sugar and an oxygen or nitrogen atom of another molecule, typically another sugar molecule). ü This type of bond à linkage of monosaccharides to form disaccharides or polysaccharides ü The hydrolysis of this bond by enzyme a-glycosidase is important for the breakdown of complex carbohydrates. The anomeric carbon à carbon atom in a sugar molecule that is bonded to both an oxygen atom in the sugar's carbonyl group (C=O) and a hydroxyl group (-OH) in the sugar's ring structure. The term "anomeric" comes from the fact that this carbon atom has a different configuration from the other carbon atoms in the sugar molecule. 51 Nerve gases like tabun and sarin are? *** a) Irreversible inhibitors of dihydrofolate reductase • • b) Reversible inhibitors of dihydrofolate reductase c) Irreversible inhibitors of acetylcholinesterase d) Reversible inhibitors of acetylcholinesterase 52 Which types of collagens are fibrillar and have the ropeline structure? *** • • a) II, IV, VII Acetylcholinesterase is an enzyme that breaks down the neurotransmitter acetylcholine. Tabun and sarin inhibit acetylcholinesterase by covalently binding to the enzyme, causing acetylcholine buildup overstimulating the nervous system. Thus, leading to seizures, respiratory failure, and ultimately, death. The inhibition of acetylcholinesterase by nerve gases is irreversible These three types of collagens are the most abundant fibrillar collagens in the body and have a characteristic rope-like structure due to their triple helix formation. ü Type I collagen is found in skin, bone, and tendon, while ü Type II collagen is found in cartilage and ü Type III collagen is found in blood vessels, skin, and internal organs. b) All types of collagens form fibrillar rope-like structures c) I, II, III d) IX XII 53 You are studying the effects of the addition potential pharmaceutical compound on the ac of your enzyme of interest. You found that the addition of the compound results in an increase of the Km reaction but does not affect the Vmax. Which of the following defines the inhibitor of the compound? ** a) Noncompetitive b) Uncompetitive c) Suicide d) Competitive • • Competitive Inhibition of enzyme à inhibitor binds to active site on enzyme. The increase in Km (enzyme substrate affinity) without any effect on Vmax (Maximum velocity of the enzyme reaction) indicates compound is competing with the substrate for binding to the active site of the enzyme. • The inhibitor and substrate compete for same binding site on the enzyme à results in increased Km value without affecting the Vmax. ü Noncompetitive and uncompetitive inhibitors affect both the Vmax and Km values. ü Suicide inhibitors, also known as irreversible inhibitors, form a covalent bond with the enzyme and permanently inactivate it, 54 Which vitamins are produced in human intestinal microflora? a) Niacin and biotin • • Biotin (vitB7) a water-soluble vitamin plays a role in the metabolism of carbohydrates, fats, and amino acids. Vit K a fat-soluble vitamin that plays a role in blood clotting and bone metabolism. ü Both of these vitamins are produced by certain bacteria that reside in the human intestinal tract. b) Folic acid and niacin c) Riboflavin and vitamin K d) Biotin and vitamin K • Carboxylate group (COO-) of aspartic and glutamic acid has pKa value around 4, thus at physiologic pH (around 7.4), they will be deprotonated and carry a negative charge while at acidic pH, they will become protonated and carry a neutral charge. • Option b) is incorrect since at basic pH, these amino acids will not become positively charged. c) At physiologic pH have neutral charge • Option c) is also incorrect as at physiologic pH, they are negatively charged. d) At acidic pH contain negatively charged carboxylase group (COO-) • Option d) is partly correct but incomplete as the term "carboxylase group" is not a scientific term, and it should be "carboxylate group." 55 Aspartic and glutamic acid? * a) At physiologic pH contain negatively charged carboxylase group (COO-) b) At basic pH are positively charged 56 Which of the following statements about protein structure is correct? * a) The information required for the correct folding of a protein is contained in the specific sequence of amino acids along the polypeptide chain b) The stability of quaternary structure in proteins is mainly a result of peptide bonds among the subunits c) Proteins consisting of one polypeptide can have quaternary structure d) The formation of disulfide bond in a protein requires that the two participating cysteine residues be adjacent to each other in primary sequence of the protein. • The specific sequence of amino acids along the polypeptide chain determines the folding of a protein, which in turn determines its structure and function. ü Option b) is incorrect because the stability of the quaternary structure in proteins is mainly a result of noncovalent interactions such as hydrogen bonding, ionic interactions, and hydrophobic interactions. ü Option c) is also incorrect since proteins consisting of one polypeptide do not have a quaternary structure; quaternary structure refers to the arrangement of multiple polypeptides in a protein complex. ü Option d) is incorrect because disulfide bond formation occurs between two cysteine residues that are not necessarily adjacent to each other in the primary sequence of the protein. 57 In the far east, beriberi is a serious health problem. It is characterized by neurologic and cardiac symptoms. Beriberi is caused by a deficiency of which of the following vitamins? a) Ethanolamine • Beriberi is a disease that occurs due to severe thiamine deficiency and is common in populations that rely heavily on polished rice as a staple food, as the milling process removes the thiamine-rich outer layers of the rice kernel. • Thiamine, an essential water-soluble vitamin plays a critical role in energy metabolism. ü It is a cofactor for several enzymes involved in the breakdown of glucose, such as pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase. ü Is also important for the proper functioning of the nervous system and the heart. • Deficiency can lead to symptoms, including neurologic such as muscle weakness, tingling, and difficulty walking, and cardiac symptoms such as rapid heart rate and heart failure. • Options a), b), and c) are incorrect as they do not refer to vitamins. ü Ethanolamine and choline are precursors for the synthesis of phospholipids, ü Glycine is a nonessential amino acid. • Glucose and galactose are both aldohexoses, but they differ in the stereochemistry at the C-4 position. Glucose has an -OH group at the C-4 position, b) Choline c) Glycine d) Thiamine (VitaminB1) 58 Which of the following statements best describes glucose? a) It is a ketose and usually exists as a furanose ring in a solution b) It is a C-4 epimer of galactose Option (a) is incorrect as glucose is an aldose, not a ketose. c) It is produced from dietary starch by the action of a-amylase Option (c) is partially correct in that glucose can be produced from dietary starch by the action of alpha-amylase, an enzyme that cleaves the alpha-1,4 glycosidic linkages in starch. However, other enzymes are also involved in the breakdown of starch to glucose, such as beta-amylase and maltase. d) It is utilized in biological systems only in the L-isomeric form Option (d) is incorrect as glucose is utilized in biological systems primarily in the Disomeric form, not the L-isomeric form. 59 Which substances act as free radical scavengers? a) Vitamins A, E, C b) Vitamins E, A, D c) Vitamins A, D d) Vitamins E, C Harpers; Vitamins & Minerals; Chapter 45: p.482: Vitamin A à Retinol, b-carotene Retinol can neutralize free radicals and reactive oxygen species (ROS) through its ability to donate hydrogen atoms. E à Tocopherols, Tocotrienols Lipid-soluble antioxidant that can prevent lipid peroxidation in cell membranes. C à Ascorbic acid Water-soluble antioxidant that can donate electrons to neutralize free radicals. • Functions b-carotene is an antioxidant Antioxidant, especially in cell membranes Coenzyme in hydroxylation of proline and lysine in collagen synthesis; antioxidant; enhances absorption of iron Option (a) is correct; Vitamins A, E, and C are all known to act as antioxidants and free radical scavengers, helping to protect cells and tissues from oxidative damage. ü Vitamin A (retinol) can neutralize free radicals and reactive oxygen species (ROS) through its ability to donate hydrogen atoms. ü Vitamin E (alpha-tocopherol) is a lipid-soluble antioxidant that can prevent lipid peroxidation in cell membranes. ü Vitamin C (ascorbic acid) is a water-soluble antioxidant that can donate electrons to neutralize free radicals. 60 What is not required for priming of DNA synthesis in Eukaryotes? a) DNA template b) RNA primer c) DNA primer d) DNA polymerase a RNA primers are not required for priming of DNA synthesis in Eukaryotes. Unlike prokaryotic DNA replication (requires RNA primers to initiate DNA synthesis), eukaryotic DNA replication is initiated by the assembly of protein complex called the pre-replication complex (pre-RC) at the origin of replication. 61 Choose the correct sentence? a) Telomeres are specific regions on DNA responsible for production of tRNA and rRNA b) Telomeres are the images of individuals complement of chromosomes arranged by size, length, shape and centromere location. • Option a) is incorrect because telomeres are not responsible for the production of tRNA and rRNA. • Option b) is also incorrect because it describes karyotypes, not telomeres. • Option c) is partially correct in describing telomeres as non-coding regions, but it does not mention their protective function. c) Telomeres are non-coding regions that play a role in regulating the expression of genes by promoting (enhancers) or inhibiting (silencers) specific sequences. d) Telomeres are located on the ends of eukaryotic chromosomes and have a protective function because DNA cannot be replicated all the way to the ends, so telomeres prevent loss of important genes 62 Which of the following sentences concerning vitamin K is false? LECTURE; vitamins all vit k; a) Vitamin K is required for the synthesis of prothrombin b) Menaquinones are found in green vegetables c) Vitamin K is produced by the intestinal microflora d) Vitamin K is required for the y-carboxylation of glutamate residues of osteocalcin in bone a) Menaquinones are found in green vegetables à is false They are made by intestinal bacteria 63 Choose the answer where both subclasses are assigned properly to enzyme classes? a) Peptidase - Ligase; peroxidase - ligase b) Aminotransferase - transferase; esterase axidoreductase c) Dehydrogenase - transferase; epimerase isomerase d) Esterase-hydrolase; dehydrogenaseoxidoreductase 64 Which vitamin functions as a coenzyme for pyruvate dehydrogenase? a) Pyridoxal phosphate b) Riboflavin c) Niacin d) Thiamine (vitamin B1) In this answer, esterase and hydrolase belong to the hydrolase class of enzymes, which catalyze the hydrolysis of various chemical bonds. Similarly, dehydrogenase and oxidoreductase belong to the oxidoreductase class of enzymes, which catalyze oxidation-reduction reactions. LECTURE; ENZYMES page.20; LECTURE; VITAMINS;page. 55 65 The most abundant protein structure is? * a) B-hairpin b) B-barrel c) c) Alfa-helix d) Beta-sheet FERRIER Page 51 & 52; A. α-Helix: • The α-helix is the most common. ü It is a spiral structure, consisting of a tightly packed, coiled polypeptide backbone core, with the side chains of the component amino acids extending outward from the central axis to avoid interfering sterically with each other. • A very diverse group of proteins contains α-helices àKERATINS ü A family of closely related, fibrous proteins ü Structure is nearly entirely α-helical. ü Major component of hair and skin, and their rigidity is determined by the number of disulfide bonds between the constituent polypeptide chains. LECTURE; PROTEINS; page.8: 66 Which of the following sentences concerning vitamin D is correct? a) The 1-alpha-hydroxylase activity is stimulated by high serum concentrations of calcium b) 25-hydroxy cholecalciferol is the major storage form of the vitamin c) 7-dehydrocholesterol undergoes a non-enzymic reaction on exposure to ultraviolet light, yielding ergocalciferol d) Calcitriol (1.25(OH)2D3) is the most potent of the vitamin D metabolites 67 Which of the following sentences is true concerning mutations? a) The exchange of DNA between chromosomes during meiosis is called mutation b) A mutation is a permanent alteration in the base sequence of the DNA c) A DNA repair process that of polynucleotides is called mutation d) a mutation is an acce