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?

<p>Lactate dehydrogenase. (A)</p> Signup and view all the answers

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

<p>Reduction of pyruvate to lactate. (D)</p> 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?

<p>Cytosolic malate dehydrogenase. (B)</p> Signup and view all the answers

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

<p>Acetyl CoA, NADH, and CO2. (B)</p> Signup and view all the answers

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

<p>Increased levels of Ca2+. (D)</p> Signup and view all the answers

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

<p>It stimulates PDH phosphorylation and inactivation. (B)</p> Signup and view all the answers

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

<p>Isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase. (D)</p> Signup and view all the answers

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

<p>Cytochrome bc and cytochrome c oxidase. (C)</p> Signup and view all the answers

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

<p>They reduce O2 to H2O. (C)</p> 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?

<p>NADH dehydrogenase and cytochrome bc. (A)</p> Signup and view all the answers

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

<p>It dephosphorylates and inactivates glycogen phosphorylase. (D)</p> Signup and view all the answers

What stimulates glycogenolysis during strenuous exercise in muscles?

<p>AMP activating glycogen phosphorylase directly. (B)</p> Signup and view all the answers

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

<p>Pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase. (D)</p> Signup and view all the answers

How is glycogenolysis stimulated in the liver during prolonged starvation?

<p>CAMP-activated protein kinase phosphorylates glycogen phosphorylase kinase. (B)</p> Signup and view all the answers

Which set of enzymes operates exclusively in glycolysis?

<p>Hexokinase, phosphofructokinase-1, and pyruvate kinase. (A)</p> Signup and view all the answers

Which enzymes operate exclusively in gluconeogenesis?

<p>Fructose bisphosphatase-1, PEP carboxykinase, and pyruvate carboxylase. (C)</p> Signup and view all the answers

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

<p>Decreased production of pyruvate by glycolysis. (A)</p> Signup and view all the answers

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

<p>Decreased levels of fructose 2,6-bisphosphate. (D)</p> Signup and view all the answers

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

<p>Severe hypoglycemia due to compromised glucose production. (D)</p> Signup and view all the answers

Which reaction produces phosphoenolpyruvate (PEP) in gluconeogenesis?

<p>Oxaloacetate + GTP → PEP + GDP + CO2. (B)</p> 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?

<p>Aldolase B deficiency leading to fructose intolerance. (B)</p> Signup and view all the answers

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

<p>Glyceraldehyde 3-phosphate and fructose 6-phosphate (A)</p> Signup and view all the answers

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

<p>Glucose 6-phosphate and 6-phosphogluconate (A)</p> Signup and view all the answers

What reaction requires reducing equivalents from NADPH?

<p>Reduction of oxidized glutathione by glutathione reductase (C)</p> Signup and view all the answers

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

<p>Increased oxidative stress due to lack of NADPH (D)</p> Signup and view all the answers

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

<p>Citrate + CoA + ATP → oxaloacetate + acetyl CoA + ADP + Pi (D)</p> Signup and view all the answers

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

<p>Insulin-stimulated dephosphorylation and activation of acetyl CoA carboxylase (C)</p> Signup and view all the answers

During prolonged aerobic exercise, which process occurs in adipocytes?

<p>Epinephrine stimulates phosphorylation and activation of hormone-sensitive lipase (B)</p> Signup and view all the answers

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

<p>144 (+8 FADH2, +8 NADH, +9 acetyl CoA) (C)</p> Signup and view all the answers

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

<p>Acetoacetyl CoA → Acetyl CoA (C)</p> Signup and view all the answers

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

<p>Ketogenic (A)</p> Signup and view all the answers

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

<p>Pyruvate and glutamate (C)</p> Signup and view all the answers

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

<p>Argininosuccinate lyase (C)</p> Signup and view all the answers

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

<p>Convert branched-chain amino acids to their α-keto acid forms (B)</p> Signup and view all the answers

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

<p>Folate (B9) and Cobalamine (B12) (D)</p> Signup and view all the answers

Which reaction leads to the production of urea?

<p>Hydrolysis of arginine's guanidino group (D)</p> Signup and view all the answers

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

<p>Glutamate (B)</p> Signup and view all the answers

Flashcards

Hexokinase vs. Glucokinase

Hexokinase is active at low glucose concentrations; glucokinase at high concentrations. Glucokinase has higher Kcat and Km.

Insulin's effect on PFK2/FBP2

Insulin stimulates dephosphorylation of PFK2/FBP2 in liver, increasing fructose-2,6-bisphosphate and thus, fructose 1,6-bisphosphate.

Glucagon's effect on PFK2/FBP2

Glucagon stimulates phosphorylation of PFK2/FBP2 in liver, reducing fructose-2,6-bisphosphate and dephosphorylating fructose 1,6-bisphosphate to fructose 6-phosphate.

Insulin's effect on Pyruvate Kinase

Insulin dephosphorylates pyruvate kinase, leading to increased pyruvate production in the liver.

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Fructose 1,6-bisphosphate effect on Pyruvate Kinase (muscle)

Increased fructose 1,6-bisphosphate stimulates pyruvate kinase activity, leading to increased pyruvate in muscle.

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Lactate Dehydrogenase in Exercising Muscle

Lactate dehydrogenase generates NAD+ by reducing pyruvate to lactate in oxygen-deprived muscle.

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Phosphorylation-Dephosphorylation Effect (PDH, Exercise)

Increased Ca2+ in exercising muscle stimulates pyruvate dehydrogenase (PDH) dephosphorylation and activation.

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Substrate-Level Phosphorylation Enzymes

Phosphoglycerate kinase and pyruvate kinase produce ATP through substrate-level phosphorylation of ADP.

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Pyruvate Dehydrogenase (PDH)

An enzyme complex that catalyzes the oxidative decarboxylation of pyruvate, converting it to acetyl-CoA.

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Oxidative Decarboxylation

A chemical reaction that removes a carboxyl group (COOH) from a molecule, typically releasing CO2 and producing a reduced coenzyme.

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NADH in PDH

High NADH levels signal to inactivate pyruvate dehydrogenase.

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TCA cycle enzymes producing NADH

Isocitrate dehydrogenase, a-ketoglutarate dehydrogenase, and malate dehydrogenase produce NADH in the TCA cycle.

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Coenzyme Q

A molecule that transfers reducing equivalents between NADH dehydrogenase and cytochrome b in the electron transport chain.

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Glycogenolysis Stimulation

During exercise, Ca2+ activates phosphorylase kinase, which activates glycogen phosphorylase, breaking down glycogen into glucose for energy. Also, AMP directly activates glycogen phosphorylase.

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Glycogenesis Activation

Insulin activates protein phosphatase, inactivating glycogen phosphorylase and activating glycogen synthase. This promotes glycogen storage.

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Electron Transport Chain

A series of protein complexes in the inner mitochondrial membrane that transfer electrons from NADH and FADH2 to oxygen, pumping protons to generate ATP.

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Glycolysis-Specific Enzymes

The enzymes hexokinase, phosphofructokinase-1 (PFK-1), and pyruvate kinase are exclusively involved in glycolysis and are not used in gluconeogenesis.

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Gluconeogenesis-Specific Enzymes

Pyruvate carboxylase, PEP carboxykinase, and fructose bisphosphatase-1 are exclusively used in gluconeogenesis, not glycolysis.

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Glucagon's Effect on Pyruvate Kinase

In the liver, glucagon-stimulated phosphorylation of pyruvate kinase leads to reduced production of pyruvate from glycolysis.

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Glucose 6-phosphatase Deficiency

Deficiency in liver glucose 6-phosphatase leads to severe hypoglycemia because it inhibits the liver's ability to release glucose into the bloodstream via both glycogenolysis and gluconeogenesis.

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Gluconeogenesis: PEP Production

In the liver, the conversion of oxaloacetate to phosphoenolpyruvate (PEP) in gluconeogenesis is catalyzed by the reaction: Oxaloacetate + GTP → PEP + GDP + CO2.

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Aldolase B Deficiency

Aldolase B deficiency can cause fructose intolerance, leading to symptoms like tremors, night sweats, and vomiting, due to fructose accumulation in the liver.

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Ketogenic Amino Acids

Amino acids broken down into acetyl-CoA or acetoacetate, which can be used for energy production or ketone body synthesis.

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Glucogenic Amino Acids

Amino acids broken down into pyruvate or TCA cycle intermediates, which can be used for glucose synthesis.

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Aminotransferase Reaction (Alanine)

An aminotransferase enzyme transfers the amino group from alanine to α-ketoglutarate, producing pyruvate and glutamate.

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Aminotransferase Reaction (Glutamate)

An aminotransferase enzyme transfers the amino group from glutamate to oxaloacetate, producing α-ketoglutarate and aspartate.

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Urea Synthesis

Urea is produced through the hydrolysis of the guanidino group of arginine, releasing ammonia and ornithine.

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Urea Cycle Nitrogen Source

The nitrogen in urea is derived from both ammonia and aspartate, both of which are initially derived from glutamate.

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Argininosuccinate Lyase Deficiency

A genetic deficiency in argininosuccinate lyase leads to hyperammonemia due to the buildup of argininosuccinate.

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Hyperammonemia Treatment

Hyperammonemia, a buildup of ammonia in the blood, is treated by restricting dietary protein and administering phenylbutyrate, which traps ammonia and removes it from the body.

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NADPH's Role in Glutathione Reduction

NADPH provides the reducing equivalents needed for the enzyme glutathione reductase to reduce oxidized glutathione (GSSG) back to its reduced form (GSH), which is essential for protecting cells from oxidative damage.

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Glucose-6-Phosphate Dehydrogenase Deficiency

A deficiency in the enzyme glucose-6-phosphate dehydrogenase (G6PD) leads to a decrease in NADPH production, making red blood cells vulnerable to oxidative stress and causing hemolytic anemia.

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Citrate's Role in Fatty Acid Synthesis

Citrate, a key intermediate of the citric acid cycle, is transported out of the mitochondria into the cytoplasm where it is cleaved by ATP-citrate lyase to provide acetyl-CoA and oxaloacetate for fatty acid synthesis.

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Insulin's Effect on Acetyl-CoA Carboxylase

Insulin, a hormone secreted in response to high blood glucose levels, stimulates the dephosphorylation and activation of acetyl-CoA carboxylase, the enzyme that catalyzes the first committed step of fatty acid synthesis.

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Epinephrine's Role in Lipolysis

Epinephrine, a hormone released during stress or exercise, stimulates the phosphorylation and activation of hormone-sensitive lipase, leading to the breakdown of stored triglycerides into fatty acids and glycerol for energy.

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FAD's Role in Beta-Oxidation

FAD (flavin adenine dinucleotide) accepts electrons during the oxidation of mitochondrial fatty acyl CoA, glycerol-3-phosphate, and succinate, generating FADH2, a high-energy electron carrier that fuels the electron transport chain.

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ATP Yield from Fatty Acid Oxidation

The ATP yield from the complete oxidation of a fatty acid depends on its chain length and degree of saturation. For example, the complete oxidation of an 18-carbon fatty acid with two double bonds (18:2) yields 144 ATP molecules.

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Unsaturated Fatty Acids and ATP Yield

Unsaturated fatty acids have fewer ATP yields compared to saturated fatty acids of the same chain length because the double bonds are already partially oxidized, reducing the number of electron carriers (NADH, FADH2) produced.

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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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Exam 3 Questions - Biochemistry PDF

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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.

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