Biochemistry Quiz: Hormonal Regulation Of Metabolism

What this quiz covers

This quiz focuses on Hormonal Regulation Of Metabolism, giving you a quick way to practice the rules, question types, and explanations that matter most for Biochemistry.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. Glucagon activates a protein phosphatase that dephosphorylates the PFK-2 domain, increasing its kinase activity.
2. Glucagon activates Protein Kinase A (PKA), which phosphorylates the enzyme, activating the FBPase-2 domain and inhibiting the PFK-2 domain. (correct answer)
3. Glucagon directly binds to the PFK-2/FBPase-2 enzyme, causing an allosteric shift that favors its FBPase-2 activity.
4. Glucagon signaling leads to the transcriptional repression of the gene encoding PFK-2/FBPase-2, reducing its overall concentration.

Explanation: Glucagon signaling increases cyclic AMP (cAMP), which activates Protein Kinase A (PKA). PKA then phosphorylates a single serine residue on the bifunctional enzyme. This phosphorylation event activates the fructose-2,6-bisphosphatase (FBPase-2) domain and simultaneously inhibits the phosphofructokinase-2 (PFK-2) domain. The net result is the breakdown of F-2,6-BP, lowering its concentration and promoting gluconeogenesis.

Question 2

1. Glucagon signaling leads to dephosphorylation and activation of L-PK, promoting the final step of glycolysis.
2. Glucagon triggers the synthesis of fructose-1,6-bisphosphate, which allosterically activates L-PK.
3. Glucagon signaling leads to PKA-mediated phosphorylation, which causes the inactivation of L-PK. (correct answer)
4. Glucagon has no direct effect on L-PK; regulation occurs solely through changes in substrate availability.

Explanation: During a fasted state signaled by glucagon, the liver must perform gluconeogenesis. To prevent a futile cycle where newly synthesized phosphoenolpyruvate (PEP) is immediately converted back to pyruvate, the final step of glycolysis must be turned off. Glucagon signaling activates PKA, which phosphorylates the liver isoform of pyruvate kinase, rendering it inactive. This ensures that PEP is directed toward glucose synthesis.

Question 3

1. Increased blood glucose from hepatic glycogenolysis, and increased lactate production from muscle glycogenolysis. (correct answer)
2. Increased blood glucose due to hepatic glycogenolysis, but no significant effect on muscle glycogen stores.
3. Decreased blood glucose due to enhanced glucose uptake by both liver and muscle tissue.
4. Increased fatty acid synthesis in the liver and increased triacylglycerol storage in adipose tissue.

Explanation: Beta-adrenergic agonists mimic epinephrine, which acts on both liver and muscle beta-receptors. In the liver, it raises blood glucose, similar to glucagon. Crucially, in muscle (which lacks glucagon receptors), it stimulates glycogenolysis. Because muscle lacks glucose-6-phosphatase, the resulting G6P enters glycolysis, producing lactate under anaerobic conditions. Therefore, the combination of hyperglycemia and muscle lactate production is characteristic of epinephrine/beta-agonist action, distinguishing it from glucagon.

Question 4

1. Increased transcription of genes for phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase.
2. Decreased transcription of the gene for the GLUT4 glucose transporter in skeletal muscle cells.
3. Increased transcription of genes for key glycolytic and lipogenic enzymes like pyruvate kinase and fatty acid synthase. (correct answer)
4. Decreased transcription of the gene for the insulin receptor to induce a state of desensitization.

Explanation: In a prolonged fed state, insulin signaling upregulates the synthesis of enzymes needed to process and store the incoming glucose. This includes increasing the transcription of genes for key glycolytic enzymes (e.g., glucokinase, pyruvate kinase) and enzymes involved in fatty acid synthesis (e.g., acetyl-CoA carboxylase, fatty acid synthase) to convert excess carbohydrate into fat for long-term storage.

Question 5

1. Insulin binding activates PKA, which phosphorylates GLUT4 transporters, causing them to move to the cell surface.
2. Insulin increases the transcription and subsequent translation of the GLUT4 gene, a slow process that builds uptake capacity.
3. Insulin acts as an allosteric activator of the GLUT4 transporter protein itself, increasing its intrinsic transport velocity.
4. Insulin triggers a signaling cascade that results in the fusion of intracellular vesicles containing GLUT4 with the plasma membrane. (correct answer)

Explanation: When you encounter questions about insulin and glucose uptake, focus on distinguishing between acute (immediate) and chronic (long-term) effects, as well as understanding the specific mechanism of glucose transporter regulation. Insulin's rapid effect on glucose uptake occurs through a well-characterized signaling pathway. When insulin binds to its receptor, it activates a cascade involving PI3K and Akt kinases, ultimately leading to the translocation of glucose transporter 4 (GLUT4) from intracellular storage vesicles to the plasma membrane. This vesicle fusion process dramatically increases the number of glucose transporters available at the cell surface within minutes, allowing enhanced glucose uptake. Answer D correctly describes this acute molecular mechanism. Answer A incorrectly suggests PKA involvement and direct phosphorylation of GLUT4. PKA is actually associated with glucagon signaling (which opposes insulin), and GLUT4 translocation doesn't require direct phosphorylation of the transporter itself. Answer B describes a chronic response involving gene transcription and translation, which takes hours to days rather than the acute timeframe the question specifies. Answer C suggests allosteric activation of existing GLUT4 transporters, but insulin's primary mechanism isn't changing transporter kinetics—it's increasing transporter number at the membrane. Remember that insulin's acute effects typically involve protein modifications and trafficking rather than gene expression changes. When you see "acute" or "immediate" in insulin questions, think translocation and phosphorylation cascades, not transcription. This distinction frequently appears on biochemistry exams testing hormone mechanisms.

Question 6

1. Increased phosphorylation of hormone-sensitive lipase leading to enhanced lipolysis
2. Increased phosphorylation of acetyl-CoA carboxylase leading to reduced fatty acid synthesis
3. Increased phosphorylation of pyruvate dehydrogenase leading to enhanced glucose oxidation (correct answer)
4. Increased phosphorylation of phosphofructokinase-2 leading to reduced glycolysis

Explanation: During fasting with high glucagon, pyruvate dehydrogenase becomes phosphorylated and INHIBITED, not enhanced. This prevents glucose oxidation and preserves glucose for the brain. Glucagon promotes gluconeogenesis, so blocking glucose oxidation makes metabolic sense. Choices A, B, and D all correctly describe fasting-state enzyme regulations where phosphorylation activates catabolic enzymes (HSL) or inhibits anabolic enzymes (ACC, PFK-2).

Question 7

1. Acetyl-CoA carboxylase (ACC).
2. Hormone-sensitive lipase (HSL). (correct answer)
3. Lipoprotein lipase (LPL).
4. Pyruvate dehydrogenase complex (PDH).

Explanation: In the absence of insulin, the inhibitory signal on hormone-sensitive lipase (HSL) in adipocytes is removed. Furthermore, glucagon and epinephrine signaling leads to the phosphorylation and activation of HSL. Active HSL hydrolyzes stored triacylglycerols, releasing large quantities of fatty acids into the bloodstream. These fatty acids are taken up by the liver and converted to acetyl-CoA, which is then used to synthesize ketone bodies, leading to ketoacidosis.

Question 8

1. Glycogen synthesis from glucose-6-phosphate.
2. Fatty acid synthesis from acetyl-CoA.
3. Activation of glycogenolysis via glycogen phosphorylase. (correct answer)
4. Glucose uptake via insulin-independent GLUT2 transporters.

Explanation: During fasting, glucagon is the primary hormonal signal for the liver to produce glucose. A key rapid response is the activation of glycogenolysis. Glucagon signaling through PKA leads to the phosphorylation and activation of glycogen phosphorylase. A non-functional glucagon receptor would block this cascade, severely impairing the liver's ability to break down glycogen and release glucose, leading to fasting hypoglycemia.

Question 9

1. Epinephrine activates adenylyl cyclase in hepatocytes, while glucagon activates a different second messenger system involving IP₃.
2. Epinephrine strongly stimulates glycogenolysis in skeletal muscle, whereas glucagon has little to no effect on skeletal muscle glycogen. (correct answer)
3. Glucagon promotes gluconeogenesis in the liver from various precursors, while epinephrine inhibits this pathway to conserve cellular energy.
4. Epinephrine's effects are mediated by phosphorylation cascades, while glucagon's effects are primarily through allosteric regulation.

Explanation: A key distinction between these hormones is tissue specificity. Skeletal muscle cells have receptors for epinephrine but lack receptors for glucagon. Therefore, epinephrine can stimulate glycogenolysis in muscle to provide fuel for glycolysis within the muscle itself, while glucagon cannot. Both hormones act on the liver to stimulate glycogenolysis and gluconeogenesis to raise blood glucose for the entire body.

Question 10

1. Increased flux through glycolysis due to elevated levels of fructose-2,6-bisphosphate.
2. Increased rates of both glycogenolysis and gluconeogenesis, mimicking a glucagon signal. (correct answer)
3. Enhanced fatty acid synthesis due to covalent activation of acetyl-CoA carboxylase.
4. Decreased activity of glycogen phosphorylase and increased activity of glycogen synthase.

Explanation: cAMP phosphodiesterase degrades cAMP. By inhibiting this enzyme, caffeine causes cAMP levels to rise, even with only basal glucagon secretion. Elevated cAMP activates Protein Kinase A (PKA). PKA phosphorylates and activates enzymes involved in glucose production (like glycogen phosphorylase) and inactivates enzymes for glucose storage (like glycogen synthase). This mimics the effects of a strong glucagon signal, promoting glucose release from the liver.

Question 11

1. Pyruvate dehydrogenase, to increase the supply of acetyl-CoA.
2. Glycogen phosphorylase, to prevent a futile cycle of glycogen breakdown.
3. Glycogen synthase, to directly catalyze the formation of glycogen. (correct answer)
4. Phosphofructokinase-1, to increase the rate of glycolysis.

Explanation: Glycogen synthase is the key enzyme for glycogen synthesis and is active in its dephosphorylated form. Insulin signaling activates Protein Phosphatase 1 (PP1), which removes the inhibitory phosphate groups from glycogen synthase, thereby activating it. While PP1 also dephosphorylates and inactivates glycogen phosphorylase (B), the direct activation of glycogen synthase (C) is the committed step for synthesis.

Question 12

1. PKA-mediated activation of phosphofructokinase-1, directly increasing glycolytic flux through the rate-limiting step.
2. PKA-mediated phosphorylation and activation of glycogen phosphorylase, providing abundant substrate for glycolysis. (correct answer)
3. PKA-mediated phosphorylation and inactivation of the muscle isoform of pyruvate kinase, redirecting flux to lactate production.
4. Epinephrine-mediated activation of protein phosphatases, which dephosphorylate and activate key glycolytic enzymes.

Explanation: The primary role of epinephrine in muscle is to mobilize internal glycogen stores for immediate energy needs. The epinephrine-cAMP-PKA cascade activates glycogen phosphorylase, which rapidly breaks down glycogen into glucose-6-phosphate. This massive increase in substrate concentration drives glycolytic flux forward through substrate-level control, providing ATP for muscle contraction. Note that the muscle isoform of pyruvate kinase is not subject to PKA-mediated phosphorylation like the liver isoform.

Question 13

1. Fructose-2,6-bisphosphate levels will remain high, favoring flux through glycolysis. (correct answer)
2. The rate of gluconeogenesis will increase significantly due to high cAMP levels.
3. Glycogen phosphorylase will be maximally phosphorylated and activated, leading to rapid glycogenolysis.
4. Pyruvate kinase will be phosphorylated and inactivated, slowing the final step of glycolysis.

Explanation: When you encounter questions about hormone signaling and enzyme inhibitors, focus on the specific signaling cascade being disrupted and trace through the downstream effects. Glucagon normally activates adenylyl cyclase, increasing cAMP levels, which then activates PKA. PKA phosphorylates key regulatory enzymes to shift metabolism toward glucose production. However, H-89 blocks PKA activity, so even though glucagon raises cAMP, the downstream phosphorylation events cannot occur. The correct answer is A because PKA normally phosphorylates and inactivates phosphofructokinase-2 (PFK-2), the enzyme that synthesizes fructose-2,6-bisphosphate. With PKA blocked, PFK-2 remains active, keeping fructose-2,6-bisphosphate levels high. This powerful allosteric activator promotes glycolysis by activating PFK-1, the rate-limiting enzyme of glycolysis. Answer B is incorrect because gluconeogenesis requires PKA-mediated phosphorylation of key enzymes like acetyl-CoA carboxylase and hormone-sensitive lipase. Without functional PKA, gluconeogenesis cannot increase despite high cAMP. Answer C is wrong because glycogen phosphorylase activation requires PKA-mediated phosphorylation of phosphorylase kinase. With PKA inhibited, this phosphorylation cascade is blocked. Answer D is incorrect because pyruvate kinase phosphorylation (which does inhibit glycolysis) also requires PKA activity. Without PKA function, pyruvate kinase remains dephosphorylated and active. Remember: when analyzing metabolic regulation questions, always identify which kinase is affected and trace through its specific target enzymes. Blocking a kinase prevents all its downstream phosphorylation events, regardless of upstream signal strength.

Question 14

1. The insulin cascade activates a protein phosphatase, which dephosphorylates ACC and shifts it to its more active polymeric state. (correct answer)
2. Insulin binds directly to an allosteric site on ACC, causing a conformational change that promotes its activation.
3. Insulin signaling increases the mitochondrial export of citrate, which acts as a required feed-forward allosteric activator of ACC.
4. The insulin cascade activates PKA, which then phosphorylates key serine residues on ACC to activate it.

Explanation: When you encounter questions about metabolic regulation, focus on how insulin promotes anabolic pathways like fatty acid synthesis while inhibiting catabolic ones. The key is understanding that insulin generally activates enzymes through dephosphorylation, opposite to what hormones like glucagon do. Acetyl-CoA carboxylase (ACC) is the rate-limiting enzyme in fatty acid synthesis, and its regulation is crucial for metabolic control. ACC exists in two forms: an inactive monomeric state when phosphorylated, and an active polymeric state when dephosphorylated. Insulin signaling activates protein phosphatases (like PP2A) that remove phosphate groups from ACC, allowing it to polymerize into long, active filaments that efficiently catalyze the conversion of acetyl-CoA to malonyl-CoA. This makes option A correct. Option B is wrong because insulin doesn't bind directly to ACC—it works through its receptor and downstream signaling cascades. Option C contains a partial truth (citrate does activate ACC allosterically), but this isn't the primary mechanism by which insulin activates the enzyme. While insulin can affect citrate levels, the direct dephosphorylation is the main regulatory mechanism. Option D makes a critical error: PKA (protein kinase A) actually phosphorylates and inactivates ACC—this is what happens during fasting states when glucagon levels are high, not during fed states when insulin dominates. Remember this pattern: insulin typically activates anabolic enzymes through dephosphorylation, while catabolic hormones like glucagon inactivate them through phosphorylation. This reciprocal regulation is fundamental to metabolic control.

Question 15

1. F-2,6-BP levels are high, which inhibits gluconeogenesis by inhibiting fructose-1,6-bisphosphatase.
2. F-2,6-BP levels are low, which in turn directly activates the enzyme phosphoenolpyruvate carboxykinase (PEPCK).
3. F-2,6-BP levels are unchanged, and gluconeogenesis is primarily driven by an increase in substrate availability.
4. F-2,6-BP levels are low, which relieves inhibition of fructose-1,6-bisphosphatase, increasing gluconeogenic flux. (correct answer)

Explanation: When analyzing metabolic regulation during fasting, focus on how insulin and glucagon exert opposing effects on key regulatory enzymes through phosphorylation cascades. The hormonal profile after 24 hours of fasting creates a coordinated shift toward glucose production. Low insulin and high glucagon activate protein kinase A (PKA), which phosphorylates and inactivates phosphofructokinase-2 (PFK-2), the enzyme responsible for synthesizing fructose-2,6-bisphosphate (F-2,6-BP). Simultaneously, PKA activates fructose-2,6-bisphosphatase, which degrades F-2,6-BP. This dual mechanism dramatically reduces F-2,6-BP levels in hepatocytes. F-2,6-BP is a potent allosteric inhibitor of fructose-1,6-bisphosphatase (F-1,6-BPase), a rate-limiting enzyme in gluconeogenesis. When F-2,6-BP levels drop, this inhibition is relieved, allowing F-1,6-BPase to function efficiently and drive gluconeogenic flux forward. This confirms answer D is correct. Answer A incorrectly suggests F-2,6-BP levels are high during fasting—this would occur in the fed state with high insulin. Answer B contains a mechanistic error: F-2,6-BP doesn't directly activate PEPCK; rather, glucagon increases PEPCK transcription independently. Answer C wrongly claims F-2,6-BP levels are unchanged—this ignores the crucial regulatory role of this metabolite during fasting. Study tip: Remember that F-2,6-BP is a "metabolic switch"—high levels favor glycolysis (fed state), while low levels favor gluconeogenesis (fasted state). Always connect hormonal signals to their downstream effects on key regulatory molecules.

Question 16

1. Hypoglycemia, decreased ketone body production, and increased liver glycogen stores.
2. Hyperglycemia in the fed state, but severe and dangerous hypoglycemia during any fasting period.
3. Normal blood glucose due to compensatory insulin release, but with extremely high levels of circulating free fatty acids.
4. Persistent hyperglycemia, depletion of liver glycogen stores, and increased rates of hepatic gluconeogenesis. (correct answer)

Explanation: When analyzing hormonal disorders, focus on the direct metabolic effects of the excess hormone and how sustained elevation disrupts normal regulatory mechanisms. Glucagon is fundamentally a catabolic hormone that mobilizes glucose during fasting states. Excessive glucagon secretion creates a metabolic environment mimicking prolonged starvation, even when the patient is well-fed. Glucagon stimulates hepatic glycogenolysis (glycogen breakdown) and gluconeogenesis (glucose synthesis from amino acids and other precursors), while simultaneously promoting lipolysis in adipose tissue. With continuous glucagon excess, liver glycogen stores become depleted as they're constantly broken down faster than they can be replenished. The liver compensates by ramping up gluconeogenesis, converting proteins and fats into glucose. This results in persistent hyperglycemia that insulin cannot adequately counteract. Option A describes hypoglycemia and increased glycogen stores, which contradicts glucagon's glucose-mobilizing effects. Option B suggests normal fed-state glucose levels, but glucagonoma causes hyperglycemia regardless of feeding status due to continuous glucose production. Option C proposes normal glucose due to compensatory insulin—while insulin levels may rise, they typically cannot overcome the sustained glucagon excess, and this option ignores glucagon's effects on glucose metabolism. The correct answer is D: persistent hyperglycemia from continuous glucose mobilization, depleted liver glycogen from constant breakdown, and increased gluconeogenesis as the liver shifts to glucose synthesis. Study tip: Remember glucagon as the "glucose mobilizer"—its excess always pushes glucose UP through glycogen breakdown and gluconeogenesis, regardless of feeding state.

Question 17

1. High insulin concentration with normal glucagon levels in the incubation medium
2. Normal insulin concentration with elevated epinephrine levels in the incubation medium
3. Insulin receptor knockout muscle fibers with normal hormone concentrations in the medium
4. AMPK inhibitor treatment with normal hormone concentrations in the incubation medium (correct answer)

Explanation: Exercise-stimulated glucose uptake depends on AMPK activation from increased AMP/ATP ratios during muscle contraction. AMPK inhibition would block this pathway regardless of hormone levels. Choice A would enhance, not impair, glucose uptake. Choice B might slightly reduce uptake but wouldn't significantly impair the contraction-stimulated mechanism. Choice C wouldn't matter since exercise-stimulated uptake is insulin-independent.

Question 18

1. Normal glucokinase activity with elevated glucose-6-phosphatase activity relative to insulin levels (correct answer)
2. Elevated glucokinase activity with normal glucose-6-phosphatase activity relative to insulin levels
3. Reduced glucokinase activity with reduced glucose-6-phosphatase activity relative to insulin levels
4. Normal glucokinase activity with reduced glucose-6-phosphatase activity relative to insulin levels

Explanation: In compensated insulin resistance, the liver maintains normal glucose production despite high insulin by developing hepatic insulin resistance. This manifests as normal glucokinase (glucose sensing remains intact) but elevated glucose-6-phosphatase activity relative to what the insulin level should produce, enabling continued glucose output. Choice B would cause hypoglycemia. Choice C would cause hyperglycemia. Choice D describes normal insulin sensitivity, not resistance.

Question 19

1. Enhanced muscle glucose uptake through increased GLUT4 translocation to the membrane
2. Increased muscle glycogen synthesis through activation of glycogen synthase kinase
3. Enhanced hepatic glucose output through activation of phosphoenolpyruvate carboxykinase expression (correct answer)
4. Increased muscle protein synthesis through activation of mTOR signaling pathways

Explanation: Epinephrine's cAMP/PKA pathway activates CREB, which increases transcription of gluconeogenic enzymes like PEPCK in the liver, promoting glucose production for the depleted runner. Choice A describes insulin's effect, not epinephrine's. Choice B is incorrect because glycogen synthase kinase actually inhibits glycogen synthesis. Choice D describes anabolic signaling inconsistent with the stress response during glycogen depletion.

Question 20

1. The prolonged insulin action is causing periodic hypoglycemia, triggering counter-regulatory hormone responses (correct answer)
2. The insulin analog has partial glucagon receptor agonist activity, stimulating stress hormone pathways
3. Improved glucose control is reducing pancreatic α-cell function, leading to compensatory adrenal activation
4. The new insulin formulation contains adjuvants that directly stimulate the hypothalamic-pituitary-adrenal axis

Explanation: Elevated cortisol and catecholamines indicate counter-regulatory hormone activation, most likely due to hypoglycemic episodes from the long-acting insulin. The afternoon fatigue supports this, as hypoglycemia often causes fatigue followed by counter-regulatory hormone surges. Choice B is implausible as insulin analogs don't have glucagon activity. Choice C is incorrect because improved glucose control wouldn't impair α-cell function. Choice D suggests an unlikely pharmaceutical mechanism.