Practice Questions (Given)

Question 1

What is the difference between catabolic and anabolic pathways?

Answer 1

Catabolic pathways break down complex molecules into simpler ones, releasing energy (exergonic). Examples include glycolysis, fatty acid oxidation, and protein degradation. Anabolic pathways synthesize complex molecules from simpler precursors, requiring energy input (endergonic). Examples include gluconeogenesis, fatty acid synthesis, and protein synthesis.

Question 2

Compared with the resting state, vigorously contracting skeletal muscle shows an increased reduction of pyruvate to lactate. True or False?

Answer 2

True

Question 3

List the three sources of plasma glucose.

Answer 3

• Dietary intake
• Glycogenolysis
• Gluconeogenesis

Question 4

What is Ketogenesis?

Answer 4

Ketogenesis is the synthesis of ketone bodies (acetoacetate, β-hydroxybutyrate, and acetone) from acetyl-CoA in the liver mitochondria.

Question 5

How is ketogenesis regulated?

Answer 5

Activated by: High fatty acid oxidation, low insulin/glucagon ratio, fasting state, high glucagon, low malonyl-CoA. Inhibited by: High insulin, fed state, high malonyl-CoA.

Question 6

What effect do ketone bodies have on brain metabolism?

Answer 6

During prolonged fasting/starvation, ketone bodies become the primary fuel for the brain, providing up to 70% of brain energy needs and sparing glucose and muscle protein.

Question 7

Describe how glucose is metabolized to pyruvate in glycolysis.

Answer 7

Overall pathway: Glucose (6C) → 2 Pyruvate (3C) through 10 enzymatic steps.

Question 8

What are the irreversible steps of glycolysis?

Answer 8

1. Hexokinase: Glucose → Glucose-6-phosphate
2. Phosphofructokinase-1: Fructose-6-phosphate → Fructose-1,6-bisphosphate
3. Pyruvate kinase: Phosphoenolpyruvate → Pyruvate

Question 9

What are the regulatory steps of glycolysis?

Answer 9

1. Hexokinase (Step 1) - inhibited by product (G6P)
2. Phosphofructokinase-1 (Step 3) - major control point
3. Pyruvate kinase (Step 10)

Question 10

The first reaction in glycolysis that results in the formation of an energy-rich compound is catalyzed by?

Answer 10

glyceraldehyde 3-phosphate dehydrogenase.

Question 11

How do insulin and glucagon affect the rate of glycolysis?

Answer 11

Insulin stimulates glycolysis; glucagon inhibits glycolysis.

Question 12

Which of the following statements is true for insulin but not for glucagon?

Answer 12

Its secretion is decreased by the catecholamines.

Question 13

What would logically be characteristic of an insulinoma?

Answer 13

Decreased glucose in the blood.

Question 14

What is the pentose phosphate pathway?

Answer 14

An alternative glucose oxidation pathway that occurs in the cytosol.

Question 15

List the products of the pentose phosphate pathway.

Answer 15

• NADPH
• Ribose-5-phosphate
• Glycolytic intermediates (G3P, F6P)

Question 16

How is cytosolic pyruvate oxidized to acetyl-CoA and CO₂ in the mitochondria?

Answer 16

Pyruvate is transported into the mitochondrial matrix and catalyzed by pyruvate dehydrogenase complex.

Question 17

What are the roles of pyruvate dehydrogenase complex (PDHc) enzymes?

Answer 17

E1 decarboxylates pyruvate; E2 transfers acetyl group to CoA; E3 regenerates oxidized lipoate.

Question 18

Describe the regulation of PDH by allosteric effectors.

Answer 18

Activated by Ca²+ and ADP; inhibited by Acetyl-CoA, NADH, and ATP.

Question 19

What are the symptoms of PDHC deficiency?

Answer 19

Lactic acidosis, neurological problems, developmental delays, muscle weakness.

Question 20

What is a treatment for thiamine deficiency?

Answer 20

Ketogenic diet and thiamine supplementation

Question 21

The reaction converting pyruvate to acetyl CoA is reversible. True or False?

Answer 21

False

Question 22

Where does the conversion of pyruvate to acetyl CoA occur?

Answer 22

Mitochondria

Question 23

What inhibits the TCA cycle dehydrogenases?

Answer 23

High NADH

Question 24

What is the overall reaction of acetyl-CoA oxidation in the TCA cycle?

Answer 24

Acetyl-CoA + 3NAD+ + FAD + GDP + Pi + 2H₂O → 2CO₂ + 3NADH + FADH₂ + GTP + CoA

Question 25

Name the enzyme that produces CO₂ from isocitrate in the TCA cycle.

Answer 25

Isocitrate dehydrogenase

Question 26

Which coenzyme is used by dehydrogenases in both glycolysis and the TCA cycle?

Answer 26

NAD+

Question 27

What are the four protein complexes in the electron transport chain?

Answer 27

* Complex I (NADH-CoQ reductase) * Complex II (Succinate-CoQ reductase) * Complex III (CoQ-cytochrome c reductase) * Complex IV (Cytochrome c oxidase)

Question 28

Which complex in the transport chain does not pump protons?

Answer 28

Complex II

Question 29

What is the role of FADH₂ in the electron transport chain?

Answer 29

Enters at Complex II and pumps fewer protons than NADH

Question 30

What is the chemiosmotic theory of oxidative phosphorylation?

Answer 30

Energy from electron transport is stored as a proton gradient, then used for ATP synthesis

Question 31

What is the significance of superoxide dismutase?

Answer 31

Converts superoxide radical to hydrogen peroxide, protecting against oxidative damage

Question 32

What is gluconeogenesis?

Answer 32

Synthesis of glucose from non-carbohydrate precursors primarily in liver and kidney cortex

Question 33

Name the bypass reactions in gluconeogenesis.

Answer 33

* Pyruvate → Oxaloacetate (pyruvate carboxylase) * Oxaloacetate → Phosphoenolpyruvate (PEPCK) * Fructose-1,6-bisphosphate → Fructose-6-phosphate (Fructose bisphosphatase-1) * Glucose-6-phosphate → Glucose (glucose-6-phosphatase)

Question 34

Which reaction is unique to gluconeogenesis?

Answer 34

Oxaloacetate → phosphoenolpyruvate

Question 35

What is the main function of the Cori cycle?

Answer 35

Regenerate NAD+ anaerobically

Question 36

What is the main product of the Cahill cycle?

Answer 36

Alanine

Question 37

Which metabolic conditions do the Cori cycle and Cahill cycle operate under?

Answer 37

* Cori Cycle: Intense exercise, hypoxia * Cahill Cycle: Fasting, starvation, prolonged exercise

Question 38

What effect does glucagon have on gluconeogenesis?

Answer 38

Activates gluconeogenesis

Question 39

What is the effect of increased NADH/NAD+ ratio on gluconeogenesis?

Answer 39

Inhibits gluconeogenesis

Question 40

What is the role of ATP synthase in oxidative phosphorylation?

Answer 40

Uses proton flow back into matrix to drive ATP synthesis

Question 41

What are the key inhibitors of the respiratory chain?

Answer 41

* Complex I: Rotenone, barbiturates * Complex II: Malonate * Complex III: Antimycin A * Complex IV: Cyanide, carbon monoxide, azide * ATP synthase: Oligomycin

Question 42

What is the role of alcohol dehydrogenase in ethanol metabolism?

Answer 42

Ethanol → Acetaldehyde (produces NADH) ## Footnote Alcohol dehydrogenase is an enzyme that catalyzes the conversion of ethanol to acetaldehyde, producing NADH in the process.

Question 43

What is the function of aldehyde dehydrogenase in ethanol metabolism?

Answer 43

Acetaldehyde → Acetate (produces NADH) ## Footnote Aldehyde dehydrogenase is responsible for converting acetaldehyde to acetate, also producing NADH.

Question 44

What is the effect of an increased NADH/NAD+ ratio on lactate and pyruvate equilibrium?

Answer 44

Shifts lactate → pyruvate equilibrium toward lactate (less substrate) ## Footnote This shift results in a decreased availability of pyruvate due to increased lactate concentration.

Question 45

What is the effect of an increased NADH/NAD+ ratio on oxaloacetate and malate equilibrium?

Answer 45

Shifts oxaloacetate ← malate equilibrium toward malate (less oxaloacetate for PEPCK) ## Footnote This results in less oxaloacetate available for gluconeogenesis.

Question 46

What is the overall result of increased NADH/NAD+ ratio on gluconeogenesis?

Answer 46

Decreased gluconeogenesis → hypoglycemia (especially in fasted state) ## Footnote The inhibition of gluconeogenesis leads to lower blood glucose levels, particularly in individuals who are fasting.

Question 47

What are the inputs of gluconeogenesis?

Answer 47

* 2 Pyruvate (or equivalent precursors) * 4 ATP * 2 GTP * 2 NADH ## Footnote These inputs are required to synthesize glucose from non-carbohydrate sources in the liver.

Question 48

What are the outputs of gluconeogenesis?

Answer 48

* 1 Glucose * 4 ADP + 4 Pi * 2 GDP + 2 Pi * 2 NAD+ ## Footnote Gluconeogenesis is energetically expensive, requiring 6 high-energy phosphates to reverse glycolysis, which only produces 2 ATP.

Question 49

What are the reasons glucose is stored as glycogen?

Answer 49

* Osmotic advantage - polymeric form doesn't affect osmolarity * Rapid mobilization - branched structure allows simultaneous glucose release * Space efficient - compact storage * Large glucose storage without increasing osmotic pressure ## Footnote Storing glucose as glycogen prevents osmotic pressure issues that would occur if glucose were stored in its free form.

Question 50

What are the steps involved in glycogen synthesis (glycogenesis)?

Answer 50

* Glucose → Glucose-6-phosphate (hexokinase/glucokinase) * G6P → Glucose-1-phosphate (phosphoglucomutase) * G1P + UTP → UDP-glucose (UDP-glucose pyrophosphorylase) * UDP-glucose added to glycogen (glycogen synthase - rate-limiting) * Branching enzyme creates α-1,6 branches ## Footnote Glycogenesis is the process of synthesizing glycogen from glucose, involving several enzymatic steps.

Question 51

What are the steps involved in glycogen breakdown (glycogenolysis)?

Answer 51

* Glycogen phosphorylase removes glucose residues as Glucose-1-phosphate * Debranching enzyme moves branches and hydrolyzes α-1,6 bonds * G1P → G6P (phosphoglucomutase) * Liver: G6P → Glucose (glucose-6-phosphatase) - released to blood * Muscle: G6P enters glycolysis (no glucose-6-phosphatase) ## Footnote Glycogenolysis allows the body to access stored glucose for energy, particularly during fasting or intense exercise.

Question 52

What hormones regulate glycogen synthesis and glycogenolysis in the liver?

Answer 52

* Glucagon (fasting): Activates phosphorylase, inactivates glycogen synthase → breakdown * Insulin (fed): Inactivates phosphorylase, activates glycogen synthase → synthesis * Epinephrine: Activates breakdown ## Footnote These hormones help maintain glucose homeostasis by regulating glycogen metabolism based on the body's energy needs.

Question 53

What hormones regulate glycogen synthesis and glycogenolysis in muscle?

Answer 53

* Epinephrine: Activates breakdown (via cAMP) * Ca²+ (contraction): Activates breakdown * Insulin: Promotes synthesis ## Footnote In muscle, the regulation of glycogen metabolism is closely tied to energy demand and muscle contraction.

Question 54

What is von Gierke disease?

Answer 54

Deficiency: Glucose-6-phosphatase Pathophysiology: Cannot release glucose from liver → severe fasting hypoglycemia, hepatomegaly, lactic acidosis, hyperuricemia, hyperlipidemia ## Footnote Von Gierke disease is a glycogen storage disease characterized by the inability to convert glycogen to glucose due to a specific enzyme deficiency.

Question 55

What is the pathophysiology of pyruvate carboxylase deficiency?

Answer 55

Deficiency: Pyruvate carboxylase (first step of gluconeogenesis) Pathophysiology: Impaired gluconeogenesis → fasting hypoglycemia, lactic acidosis, developmental delay, failure to thrive ## Footnote This condition affects gluconeogenesis and the TCA cycle due to the inability to convert pyruvate to oxaloacetate.

Question 56

What is the mechanism behind alcohol-induced hypoglycemia?

Answer 56

Increased NADH/NAD+ ratio from ethanol metabolism Pathophysiology: Inhibits gluconeogenesis, depletes glycogen stores, hypoglycemia especially in fasted/malnourished individuals ## Footnote Alcohol metabolism affects glucose production and storage, leading to hypoglycemia.

Question 57

Where are the major glycogen storage sites in the body?

Answer 57

* Liver: ~100-120g (10% of liver mass) * Skeletal Muscle: ~400-500g (1-2% of muscle mass) * Other tissues: Small amounts in cardiac muscle, kidney, brain (limited) ## Footnote The liver and skeletal muscle are the primary sites for glycogen storage, with distinct functions in glucose regulation and energy provision.

Question 58

What is the function of glycogen stored in the liver?

Answer 58

Maintain blood glucose ## Footnote The liver can release free glucose into the bloodstream, helping to regulate blood sugar levels.