Exam 3 Questions - Biochemistry PDF

Exam 3 Questions- Biochemistry Part 1 1. What is the relationship between hexokinase (HK) and glucokinase (GK)? a. Answer: GK optimized for high flux glucose due to its increased Kcat and Km; HK optimized for low flux glucose due to its decreased Km. 2. In the liver, whi...

Exam 3 Questions- Biochemistry Part 1 1. What is the relationship between hexokinase (HK) and glucokinase (GK)? a. Answer: GK optimized for high flux glucose due to its increased Kcat and Km; HK optimized for low flux glucose due to its decreased Km. 2. In the liver, which results from insulin-stimulated dephosphorylation of the bifunctional enzyme phosphofructokinase-2/fructose bisphosphatase-2 (PFK2/FBP2)? a. Answer: Increased fructose 2,6-bisphosphate; Increased fructose 1,6-bisphosphate. 3. In the liver, which results from glucagon-stimulated phosphorylation of the bifunctional enzyme phosphofructokinase-2/fructose bisphosphatase-2 (PFK2/FBP2)? a. Answer: Fructose 1,6-bisphosphate is dephosphorylated to fructose 6-phosphate. 4. In the liver, which results from insulin-stimulated dephosphorylation of pyruvate kinase? a. Answer: Increased pyruvate. 5. In muscle, which results from increased levels of fructose 1,6-bisphosphate effect on pyruvate kinase? a. Answer: Increased pyruvate. 6. In vigorously exercising, oxygen depleted muscle, which enzyme provides the majority supply of NAD+ for oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate? a. Answer: Lactate dehydrogenase. 7. In vigorously exercising, oxygen depleted muscle, which reaction provides the majority supply of NAD+ for oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate? a. Answer: Reduction of pyruvate to lactate. 8. Which pair of enzymes have the uncanny ability to generate ATP by utilizing substrate-level phosphorylation of ADP? a. Answer: Phosphoglycerate kinase and pyruvate kinase. Part 2 1. In resting and well oxygenated muscle, which reaction provides the majority supply of NAD+ for oxidation of glyceraldehyde 3-phosphate to 1,3- bisphosphoglycerate? a. Answer: Reduction of oxaloacetate to malate in cytosol. 2. In resting and well oxygenated muscle, which enzyme provides the majority supply of NAD+ for oxidation of glyceraldehyde 3-phosphate to 1,3- bisphosphoglycerate? a. Answer: Cytosolic malate dehydrogenase. 3. Which is/are products) of the pyruvate dehydrogenase complex (PDH) reaction? a. Answer: CO2 +acetyl CoA +NADH 4. Which are substrates of the pyruvate dehydrogenase complex (PDH) reaction? a. Answer: Pyruvate + CoA + NAD+ 5. In exercising muscle, which occurs with pyruvate dehydrogenase (PDH)? a. Answer: Increased Ca2+ stimulates PDH dephosphorylation and activation. 6. In well-fed, resting muscle, which occurs with pyruvate dehydrogenase (PDH)? a. Answer: Increased NADH stimulates PDH phosphorylation and inactivation. 7. Which relates pyruvate dehydrogenase and a-ketoglutarate dehydrogenase? a. Answer: Both catalyze oxidative decarboxylation using TPP, lipoamide, CoA, FAD, and NAD+. 8. Which pair of enzymes BOTH catalyze oxidative decarboxylation using TPP, lipoamide, CoA, FAD, and NAD+? a. Answer: Pyruvate dehydrogenase and a- ketoglutarate dehydrogenase. 9. In the TCA cycle, which set of enzymes ALL produce NADH? a. Answer: Isocitrate dehydrogenase, a- ketoglutarate dehydrogenase, and malate dehydrogenase. 10. In the TCA cycle, which pair of enzymes produce BOTH NADH and CO2? a. Answer: Isocitrate dehydrogenase and a- ketoglutarate dehydrogenase. 11. In mitochondrial electron transport, which transfers reducing equivalents between NADH dehydrogenase and cytochrome ba? a. Answer: Coenzyme Q.  12. For transfer of reducing equivalents from FADH2 through the electron transport chain, which molecules pump protons out of the mitochondrial matrix to drive ATP synthesis? a. Answer: Cytochrome bc, (Complex Ill) and cytochrome c oxidase (Complex IV). 13. For transfer of reducing equivalents from NADH through the electron transport chain, which molecules pump protons out of the mitochondrial matrix to drive ATP synthesis? a. Answer: NADH dehydrogenase (Complex 1), cytochrome bc, (Complex IIl), and cytochrome c oxidase (Complex IV). 14. Which is the fate of reducing equivalents from NADH that enter the mitochondrial electron transport chain? a. Answer: O2 is reduced to H2O by cytochrome c oxidase. 15. What is the fate of reducing equivalents from FADH, that enter the mitochondrial electron transport chain? a. Answer: O2 is reduced to H2O by cytochrome c oxidase. Part 3 1. After feeding, how is glycogenesis stimulated in both liver and muscle? a. Answer: Insulin activates protein phosphatase, which dephosphorylates and inactivates both glycogen phosphorylase and glycogen phosphorylase kinase; and dephosphorylates and activates glycogen synthase. 2. During strenuous exercise, how is glycogenolysis stimulated in muscle? a. Answer: Ca2+-bound calmodulin activates phosphorylase kinase, which phosphorylates and activates glycogen phosphorylase; AMP directly activates glycogen phosphorylase. 3. During prolonged starvation, how is glycogenolysis stimulated in the liver? a. Answer: CAMP-activated protein kinase phosphorylates and activates glycogen phosphorylase kinase, which phosphorylates and activates glycogen phosphorylase. 4. Which set of enzymes operate exclusively in glycolysis, i.e., NOT gluconeogenesis? a. Answer: Hexokinase, phosphofructokinase-1, and pyruvate kinase. 5. Which set of enzymes operate exclusively in gluconeogenesis, i.e., NOT glycolysis? a. Answer: Pyruvate carboxylase, PEP carboxykinase, and fructose bisphosphatase-1.  6. In the liver, which is the immediate consequence of glucagon-stimulated phosphorylation of pyruvate kinase? a. Answer: Decreased production of pyruvate by glycolysis. 7. In the liver, which is the immediate consequence of glucagon-stimulated phosphorylation of the bifunctional enzyme, phosphofructokinase-2/fructose bisphosphatase-2? a. Answer: Decreased levels of fructose 2,6- bisphosphate. 8. Which is the consequence of liver glucose 6- phosphatase deficiency? a. Answer: Severe hypoglycemia, since glucose production and release from liver by either glycogenolysis or gluconeogenesis is compromised. 9. In the liver, which reaction produces phosphoenolpyruvate (PEP) in gluconeogenesis? a. Answer: Oxaloacetate +GTP → PEP +GDP +CO2 Part 4 1. A mother began weaning her 4-month old boy off breast milk by bottle feeding orange juice. Some time afterward, the child broke into tremors, night sweats, and vomiting. Doctor's examination revealed an enlarged liver. Which most likely explains? a. Answer: Aldolase B deficiency. 2. An otherwise normal healthy child became increasingly thirsty with increased frequency of urination. Concerned about the possibility of an early onset of juvenile Type Idiabetes, urine analysis revealed minimal glucose, but elevated fructose. Which most likely explains? a. Answer: Fructokinase deficiency. 3. A Female with galactose 1-phosphate uridyltransferase deficiency grows up to be a perfectly healthy young lady by avoiding lactose-containing products, e.g., dairy, her entire life. On becoming pregnant, she began to worry whether she would be capable of producing mother's milk. Which explains why her milk production will be normal? a. Answer: UDP-galactose can be produced from UDP-glucose by UDP-hexose 4-epimerase. 4. Under conditions when the need for NADPH is minimal, which pair of metabolic intermediates yield production of ribose 5-phosphate for nucleotide biosynthesis? a. Answer: Glyceraldehyde 3-phosphate and fructose 6-phosphate. 5. Under conditions when the need for ribose 5-phosphate is minimal, which pair of metabolic intermediates yield production of NADPH?  a. Answer: Glucose 6-phosphate and 6- phosphogluconate. 6. Which requires reducing equivalents from NADPH? a. Answer: Reduction of oxidized glutathione by glutathione reductase. 7. The summer before starting his first year of medical school, a young man decided to travel and explore a remote area of India where malaria is endemic. By standard measures, he began an oral regimen of primaquine, a highly effective antimalarial that is a strong oxidant. Soon thereafter, he became very weak and fainted. Blood analysis showed very low hemoglobin and hematocrit values due to hemolysis. Which best explains this case of acute onset hemolytic anemia? a. Answer: Decreased NADPH due to glucose 6-phosphate dehydrogenase deficiency. Part 5 1. In liver and adipose, which reaction provides immediate starting materials to initiate fatty acid synthesis? a. Answer: Citrate + CoA + ATP →oxaloacetate + acetyl CoA +ADP + Pi (by ATP-citrate lyase). 2. In liver and adipose, which regulates fatty acid synthesis after enjoying Holiday celebration dinner followed by consumption of two large pieces of cake? a. Answer: Insulin stimulated dephosphorylation and activation of acetyl CoA carboxylase. 3. During periods of sustained aerobic exercise, which occurs in adipocytes? a. Answer: Epinephrine stimulated phosphorylation and activation of hormone sensitive lipase. 4. Which molecule(s) is/are oxdized by FAD to produce FADH,? a. Answer: Mitochondrial faty acyl CoA, glycerol -3 phosphate, and succinate. 5. During periods of sustained aerobic exercise, which most occurs in muscle? a. Answer: Oxidation of3-hydroxyacy| CoAto 3 ketoacyl CoA (one of the steps in B-oxidation, step 4 on P3L5 S13). 6. Which is the ATP(+GTP) yield for complete oxidation of fatty acyl 18:2(9,12) CoA? a. Answer: 144. (+8 FADH2, +8 NADH, +9 actyl CoA, 2-X unsaturated double bonds (FADH2))  7. Which is the ATP(+GTP) yield for complete oxidation of fatty acyl 18:3(9,12, 15) CoA? a. Answer: 142. (+8 FADH2, +8 NADH, +9 actyl COA, -3X unsaturated double bonds (FADH2)) 8. In MUSCLE during periods of starvation, which is the outcome of fatty acid oxidation? a. Answer: Acetoacetyl CoA →2 acetyl CoA. 9. In LIVER during periods of starvation, which is the outcome of fatty acid oxidation? a. Answer: Acetoacetyl CoA →HMG CoA → acetoacetate Part 6 1. Which is the term for amino acids whose catabolism yields either acetyl CoA or acetoacetate? a. Answer: Ketogenic. 2. Which is the term for amino acids whose catabolism yields pyruvate or one of the intermediates of the TCA cycle? a. Answer: Glucogenic. 3. Which results from an aminotransferase-catalyzed reaction between alanine and a-ketoglutarate? a. Answer: Pyruvate and glutamate. 4. Which results from an aminotransferase-catalyzed reaction between glutamate and oxaloacetate? a. Answer: a-Ketoglutarate and aspartate. 5. Which reaction produces urea? a. Answer: Hydrolysis of side chain guanidino of arginine. 6. Urea is synthesized from CO2 and nitrogen from two different sources, ammonia and aspartate. Which is the immediate source of nitrogen found in both ammonia and aspartate? a. Answer: Glutamate. 7. For a newborn with rapidly developing hyperammonemia and marked elevation of argininosuccinate, which enzyme is most likely to be deficient?  a. Answer: Argininosuccinate lyase. 8. Genetic deficiencies in urea cycle enzymes lead to "congenital" hyperammonemia during the first weeks following birth. Which best describes recommended treatment options? a. Answer: Restriction of dietary protein and administration of phenylbutyrate. 9. In muscle, which enzyme requires pyridoxyl phosphate (PLP) and catalyzes conversion of branched-chain amino acids, i.e., Leu, Val, and Ile, to their a-keto acid forms? a. Answer: Branched-chain aminotransferase. 10. In muscle, which enzyme requires TPP, lipoamide, CoA, FAD, and NAD+ and catalyzes oxidative decarboxylation in the branched-chain amino acid catabolic pathway? a. Answer: Branched-chain a-keto acid dehydrogenase. 11. Which vitamins are required as precursors for coenzyme(s) used to convert homocysteine to methionine? a. Answer: Folate (B9) and Cobalamine (B12) 12. Which vitamins are required as precursors for coenzyme(s) used to convert homocysteine to cysteine? a. Answer: Pyridoxine (B6). 13. Which is the most likely explanation for high serum levels of phenylpyruvate, phelyacetate, and phenyllactate in a patient that shows normal amounts of phenylalanine hydroxylase activity? a. Answer: Deficiency in dihydropteridine (BH2) reductase. 14. Which is the most likely explanation for high serum levels of pheny|pyruvate, phelyacetate, and phenyllactate in a patient that shows normal amounts of dihydropteridine (BH2) reductase activity? a. Answer: Deficiency in phenylalanine hydroxylase. 15. Which list contains compounds whose serum levels would AL be decreased by deficiency in dihydropteridine (BH2) reductase? a. Answer: Tyrosine, DOPA, dopamine, 5- hydroxytryptophan, and serotonin.