Biochemistry Exam 3 Questions

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Questions and Answers

What primarily distinguishes glucokinase (GK) from hexokinase (HK)?

GK has a lower Km and Kcat than HK.

HK shows no significant preference for low glucose concentrations.

HK functions optimally in high glucose concentrations.

GK exhibits higher Kcat and Km values, making it more efficient for high flux glucose. (correct)

What effect does insulin-stimulated dephosphorylation of PFK2/FBP2 have in the liver?

Decreased levels of fructose 2,6-bisphosphate.

No effect on fructose metabolism.

Increased levels of pyruvate.

Increased levels of fructose 2,6-bisphosphate and fructose 1,6-bisphosphate. (correct)

What is a consequence of glucagon-stimulated phosphorylation of PFK2/FBP2 in the liver?

Increased activity of pyruvate kinase.

Fructose 1,6-bisphosphate conversion to lactate.

Inactivation of lactate dehydrogenase.

Fructose 1,6-bisphosphate is converted to fructose 6-phosphate. (correct)

Which enzyme is primarily responsible for producing NAD+ in oxygen-depleted, vigorously exercising muscle?

Lactate dehydrogenase. Signup and view all the answers

In the scenario of muscle exertion, what key reaction provides NAD+ for oxidation of glyceraldehyde 3-phosphate?

Reduction of pyruvate to lactate. Signup and view all the answers

In resting and well-oxygenated muscle, which enzyme primarily supplies NAD+ for glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate oxidation?

Cytosolic malate dehydrogenase. Signup and view all the answers

What are the primary products of the pyruvate dehydrogenase complex (PDH) reaction?

Acetyl CoA, NADH, and CO2. Signup and view all the answers

What stimulates dephosphorylation and activation of pyruvate dehydrogenase (PDH) during exercise?

Increased levels of Ca2+. Signup and view all the answers

What effect does increased NADH have on pyruvate dehydrogenase (PDH) activity?

It stimulates PDH phosphorylation and inactivation. Signup and view all the answers

Which enzymes in the TCA cycle produce both NADH and CO2?

Isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase. Signup and view all the answers

Which complexes of the electron transport chain pump protons when transferring reducing equivalents from FADH2?

Cytochrome bc and cytochrome c oxidase. Signup and view all the answers

What is the primary fate of reducing equivalents from NADH entering the mitochondrial electron transport chain?

They reduce O2 to H2O. Signup and view all the answers

Which molecules are primarily responsible for driving ATP synthesis through proton pumping when reducing equivalents from NADH pass through the electron transport chain?

NADH dehydrogenase and cytochrome bc. Signup and view all the answers

How does insulin stimulate glycogenesis in both liver and muscle tissues?

It dephosphorylates and inactivates glycogen phosphorylase. Signup and view all the answers

What stimulates glycogenolysis during strenuous exercise in muscles?

AMP activating glycogen phosphorylase directly. Signup and view all the answers

Which pair of enzymes both catalyze oxidative decarboxylation using common cofactors?

Pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase. Signup and view all the answers

How is glycogenolysis stimulated in the liver during prolonged starvation?

CAMP-activated protein kinase phosphorylates glycogen phosphorylase kinase. Signup and view all the answers

Which set of enzymes operates exclusively in glycolysis?

Hexokinase, phosphofructokinase-1, and pyruvate kinase. Signup and view all the answers

Which enzymes operate exclusively in gluconeogenesis?

Fructose bisphosphatase-1, PEP carboxykinase, and pyruvate carboxylase. Signup and view all the answers

What is the immediate consequence of glucagon-stimulated phosphorylation of pyruvate kinase in the liver?

Decreased production of pyruvate by glycolysis. Signup and view all the answers

Which effect does glucagon-stimulated phosphorylation of phosphofructokinase-2/fructose bisphosphatase-2 have in the liver?

Decreased levels of fructose 2,6-bisphosphate. Signup and view all the answers

What severe condition may result from liver glucose 6-phosphatase deficiency?

Severe hypoglycemia due to compromised glucose production. Signup and view all the answers

Which reaction produces phosphoenolpyruvate (PEP) in gluconeogenesis?

Oxaloacetate + GTP → PEP + GDP + CO2. Signup and view all the answers

Which condition is most likely to explain tremors, night sweats, and vomiting in a child after exposure to orange juice?

Aldolase B deficiency leading to fructose intolerance. Signup and view all the answers

Which pair of metabolic intermediates produces ribose 5-phosphate when the need for NADPH is minimal?

Glyceraldehyde 3-phosphate and fructose 6-phosphate Signup and view all the answers

Which pair of intermediates yields NADPH when ribose 5-phosphate production is minimal?

Glucose 6-phosphate and 6-phosphogluconate Signup and view all the answers

What reaction requires reducing equivalents from NADPH?

Reduction of oxidized glutathione by glutathione reductase Signup and view all the answers

What explains the case of acute onset hemolytic anemia in the individual taking primaquine?

Increased oxidative stress due to lack of NADPH Signup and view all the answers

Which reaction provides starting materials for fatty acid synthesis in liver and adipose tissue?

Citrate + CoA + ATP → oxaloacetate + acetyl CoA + ADP + Pi Signup and view all the answers

What regulates fatty acid synthesis after a holiday meal in the liver and adipose tissue?

Insulin-stimulated dephosphorylation and activation of acetyl CoA carboxylase Signup and view all the answers

During prolonged aerobic exercise, which process occurs in adipocytes?

Epinephrine stimulates phosphorylation and activation of hormone-sensitive lipase Signup and view all the answers

What is the ATP (+GTP) yield for complete oxidation of fatty acyl 18:2(9,12) CoA?

144 (+8 FADH2, +8 NADH, +9 acetyl CoA) Signup and view all the answers

What is the outcome of fatty acid oxidation in muscle during periods of starvation?

Acetoacetyl CoA → Acetyl CoA Signup and view all the answers

What is the term for amino acids whose catabolism yields acetyl CoA or acetoacetate?

Ketogenic Signup and view all the answers

What results from the reaction catalyzed by an aminotransferase between alanine and α-ketoglutarate?

Pyruvate and glutamate Signup and view all the answers

Which enzyme is likely to be deficient in a newborn with rapidly developing hyperammonemia and elevated argininosuccinate?

Argininosuccinate lyase Signup and view all the answers

What is the role of the enzyme branched-chain aminotransferase in the muscle?

Convert branched-chain amino acids to their α-keto acid forms Signup and view all the answers

Which vitamins are necessary as precursors for the conversion of homocysteine to methionine?

Folate (B9) and Cobalamine (B12) Signup and view all the answers

Which reaction leads to the production of urea?

Hydrolysis of arginine's guanidino group Signup and view all the answers

What is the immediate source of nitrogen found in ammonia and aspartate used for urea synthesis?

Glutamate Signup and view all the answers

Study Notes

Exam 3 Questions - Biochemistry

Hexokinase (HK) and Glucokinase (GK): Glucokinase is optimized for high glucose flux, due to a higher Kcat and Km. Hexokinase is optimized for low glucose flux due to a lower Km.
Insulin-stimulated De-phosphorylation (Liver): Insulin stimulation leads to dephosphorylation of PFK2/FBP2, increasing fructose 2,6-bisphosphate and fructose 1,6-bisphosphate.
Glucagon-stimulated Phosphorylation (Liver): Glucagon stimulation causes phosphorylation of PFK2/FBP2, dephosphorylating fructose 1,6-bisphosphate into fructose 6-phosphate.
Insulin-stimulated De-phosphorylation (Pyruvate Kinase): Insulin-stimulated dephosphorylation of pyruvate kinase leads to increased pyruvate production.
Fructose 1,6-bisphosphate Effect on Pyruvate Kinase (Muscle): Increased fructose 1,6-bisphosphate in muscle increases pyruvate kinase activity, resulting in increased pyruvate production.
Oxygen Depleted Muscle: Enzyme for NAD+ Supply: Lactate dehydrogenase provides NAD+ for the oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate in vigorously exercising, oxygen-depleted muscle.
Oxygen Depleted Muscle: Major Reaction for NAD+ Supply: The reduction of pyruvate to lactate is the major reaction that provides NAD+ for the oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate.
ATP Generation by Substrate-Level Phosphorylation: Phosphoglycerate kinase and pyruvate kinase generate ATP through substrate-level phosphorylation.

Part 2

NAD+ Supply in Resting Muscle: Cytosolic malate dehydrogenase provides NAD+ for the oxidation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate in resting, well-oxygenated muscle.
Pyruvate Dehydrogenase Complex (PDH) Reaction Products: The PDH reaction produces CO2, acetyl CoA, and NADH.
Pyruvate Dehydrogenase Complex (PDH) Substrates: The PDH reaction uses pyruvate, CoA, and NAD+.
Exercise and PDH Activation/Inactivation: Increased calcium (Ca2+) stimulates de-phosphorylation and activation of pyruvate dehydrogenase (PDH) in exercise. NADH leads to phosphorylation and inactivation of PDH in resting muscle.
Relationship between Pyruvate Dehydrogenase and a-Ketoglutarate Dehydrogenase: Both enzymes catalyze oxidative decarboxylation using TPP, lipoamide, CoA, FAD, and NAD+.
TCA Cycle Enzymes Producing NADH: Isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, and malate dehydrogenase produce NADH in the TCA cycle.
TCA Cycle Enzymes Producing NADH and CO2: Isocitrate dehydrogenase and α-ketoglutarate dehydrogenase both produce NADH and CO2 in the TCA cycle.

Part 3

Glycogenesis Stimulation (Liver and Muscle, After Feeding): Insulin activates protein phosphatase, which deactivates glycogen phosphorylase, deactivates glycogen phosphorylase kinase, and activates glycogen synthase.
Glycogenolysis Stimulation (Muscle, During Strenuous Exercise): Ca2+-bound calmodulin activates phosphorylase kinase, which phosphorylates and activates glycogen phosphorylase; AMP directly activates glycogen phosphorylase.
Glycogenolysis Stimulation (Liver, During Prolonged Starvation): CAMP-activated protein kinase phosphorylates and activates glycogen phosphorylase kinase, which phosphorylates and activates glycogen phosphorylase.
Exclusive Glycolysis Enzymes: Hexokinase, phosphofructokinase-1, and pyruvate kinase.
Exclusive Gluconeogenesis Enzymes: Pyruvate carboxylase, PEP carboxykinase, and fructose bisphosphatase-1.

Part 4

Possible Explanation for a 4-month-old Boy's Symptoms: Aldolase B deficiency.
Possible Explanation for an Otherwise Healthy Child's Symptoms: Fructokinase deficiency.
UDP-Galactose Production in Pregnancy: UDP-hexose 4-epimerase produces UDP-galactose.
Metabolic Intermediates for NADPH Production: Glyceraldehyde 3-phosphate and fructose 6-phosphate.

Part 5

Fatty Acid Synthesis Starting Materials: Citrate + CoA + ATP → oxaloacetate + acetyl CoA +ADP + Pi (through ATP-citrate lyase).
Regulation of Fatty Acid Synthesis Insulin stimulated de-phosphorylation and activation of acetyl CoA carboxylase.
Aerobic Exercise and Adipocytes: Epinephrine stimulates the phosphorylation and activation of hormone sensitive lipase.
FAD and NADH Production in Cells: Mitochondrial fatty acyl CoA, glycerol -3 phosphate, and succinate are oxidized by FAD to produce FADH2.
B-oxidation Steps in Muscle: The oxidation of 3-hydroxyacyl CoA to 3-ketoacyl CoA is part of B-oxidation.
Fatty Acyl 18:2 Oxidation Yield: 144 ATP (+8 FADH2, +8 NADH, +9 actyl CoA, 2-X unsaturated double bonds (FADH2)).

Part 6

Ketogenic Amino Acids: Amino acids that yield acetyl CoA or acetoacetate during catabolism.
Glucogenic Amino Acids: Amino acids that yield pyruvate or intermediates of the TCA cycle during catabolism.
Alanine and a-ketoglutarate Reaction: The reaction between alanine and α-ketoglutarate yields pyruvate and glutamate.
Glutamate and Oxaloacetate Reaction: The reaction between glutamate and oxaloacetate yields α-ketoglutarate and aspartate.
Urea Production: Urea is produced from the hydrolysis of a side chain guanidino of arginine.

Part 7

Genetic Deficiencies in Urea Cycle: Lead to "congenital" hyperammonemia during the first weeks following birth. Treatments include restricting dietary protein and administering phenylbutyrate.
Branched-Chain Amino Acid Enzyme: Branched-chain aminotransferase.
Branched-Chain Amino Acid Enzyme for Oxidative Decarboxylation: Branched-chain α-keto acid dehydrogenase.
Homocysteine to Methionine Conversion Enzymes: Folate (B9) and Cobalamine (B12).
Homocysteine to Cysteine Conversion Enzyme: Pyridoxine (B6).
Phenylalanine Hydroxylase Deficiency Symptoms: High serum levels of phenylpyruvate, phenyl acetate, and phenyllactate.
Enzyme Deficiency with decreased Serotonin & Tyrosine: Dihydropteridine (BH2) reductase.

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Test your knowledge on key concepts in biochemistry, focusing on enzyme activities related to glucose metabolism. Explore the roles of Hexokinase, Glucokinase, and the effects of insulin and glucagon on metabolic pathways. This quiz is essential for mastering the biochemical regulation of energy production.