GLUCONEOGENESIS & CORI CYCLE_241223_100224

What is the primary location for gluconeogenesis?

• A) Muscles

• B) Liver

• C) Brain

• D) Adipose tissue
  

• Answer: B
  Explanation: Gluconeogenesis primarily occurs in the liver to produce glucose during fasting or low carbohydrate intake, helping maintain blood glucose levels for energy.

Which enzyme converts pyruvate to oxaloacetate during gluconeogenesis?

• A) Pyruvate dehydrogenase

• B) Pyruvate carboxylase

• C) Phosphoenolpyruvate carboxykinase (PEPCK)

• D) Hexokinase

Answer: B
Explanation: Pyruvate carboxylase catalyzes the conversion of pyruvate to oxaloacetate in the mitochondria, bypassing the irreversible step of pyruvate kinase in glycolysis.

What is the primary substrate used during the Cori cycle?

• A) Glycerol

• B) Lactate

• C) Alanine

• D) Fructose

Answer: B
Explanation: Lactate is produced in muscles during anaerobic respiration and transported to the liver for conversion back to glucose in the Cori cycle.

Which hormone inhibits gluconeogenesis?

• A) Glucagon

• B) Glucocorticoids

• C) Insulin

• D) Epinephrine

Answer: C
Explanation: Insulin suppresses gluconeogenesis by inhibiting key enzymes, promoting glucose utilization, and storage as glycogen.

Which of the following is NOT a substrate for gluconeogenesis?

• A) Lactate

• B) Oxaloacetate

• C) Glycogen

• D) Alanine

Answer: C
Explanation: Glycogen is a stored form of glucose and not a precursor for gluconeogenesis. The process uses non-carbohydrate sources like lactate, amino acids, and glycerol.

What is the role of glucocorticoids in gluconeogenesis?

• A) Inhibit glycolysis

• B) Stimulate gluconeogenic enzymes

• C) Reduce blood glucose levels

• D) Enhance lactate production

Answer: B
Explanation: Glucocorticoids stimulate the synthesis of gluconeogenic enzymes like PEPCK and increase substrate availability by breaking down muscle proteins.

Which enzyme removes phosphate from glucose-6-phosphate in gluconeogenesis?

• A) Fructose-1,6-bisphosphatase

• B) Pyruvate carboxylase

• C) Glucose-6-phosphatase

• D) Phosphofructokinase

Answer: C
Explanation: Glucose-6-phosphatase catalyzes the final step of gluconeogenesis, converting glucose-6-phosphate into free glucose for release into the bloodstream.

What happens if lactate accumulates in muscles during exercise?

• A) Enhances energy production

• B) Causes cramps

• C) Prevents fatigue

• D) Decreases glucose synthesis

Answer: B
Explanation: Lactate buildup in muscles lowers pH, causing cramps and discomfort, commonly experienced during strenuous exercise.

Which pathway provides glucose for the Cori cycle?

• A) Glycolysis

• B) Gluconeogenesis

• C) TCA cycle

• D) Pentose phosphate pathway

Answer: B
Explanation: Gluconeogenesis in the liver converts lactate back to glucose, which is then transported to muscles during the Cori cycle.

How does insulin regulate gluconeogenesis?

• A) Activates PEPCK

• B) Inhibits gluconeogenic enzymes

• C) Promotes glycerol utilization

• D) Stimulates oxaloacetate formation

Answer: B
Explanation: Insulin inhibits gluconeogenic enzymes like PEPCK and glucose-6-phosphatase, ensuring glucose is used for energy or stored rather than synthesized.

Gluconeogenesis is a complete reversal of glycolysis.

Answer: False
Explanation: Gluconeogenesis bypasses glycolysis' irreversible steps using unique enzymes like PEPCK and glucose-6-phosphatase.

The brain and RBCs can synthesize glucose.

• Answer: False
  Explanation: Both brain and RBCs rely on glucose from other tissues, as they lack the pathways to synthesize it.

Glucagon stimulates gluconeogenesis.

Answer: True
Explanation: Glucagon increases the expression of gluconeogenic enzymes like PEPCK, promoting glucose synthesis.

Lactate is a product of anaerobic metabolism in muscles.

Answer: True
Explanation: Under low oxygen conditions, pyruvate is converted to lactate in muscles to regenerate NAD+ for glycolysis.

Glycerol is a gluconeogenic substrate.

Answer: True
Explanation: Glycerol, derived from adipose tissue, is converted to dihydroxyacetone phosphate (DHAP), an intermediate in gluconeogenesis.

The Cori cycle occurs primarily in adipose tissue.

Answer: False
Explanation: The Cori cycle involves muscles (lactate production) and the liver (lactate conversion to glucose).

Glucocorticoids decrease blood glucose levels.

Answer: False
Explanation: Glucocorticoids enhance gluconeogenesis, increasing blood glucose levels to meet energy demands during stress.

Insulin inhibits gluconeogenesis.

Answer: True
Explanation: Insulin promotes glycolysis and glycogen storage while suppressing gluconeogenesis.

Pyruvate must enter the mitochondria to initiate gluconeogenesis.

Answer: True
Explanation: Pyruvate is converted to oxaloacetate in mitochondria, the first step in gluconeogenesis.

The liver converts lactate to glucose in the Cori cycle.

Answer: True
Explanation: In the Cori cycle, lactate from muscles is transported to the liver, oxidized to pyruvate, and used to synthesize glucose.

Define gluconeogenesis.

Answer: Gluconeogenesis is the biochemical process by which glucose is synthesized from non-carbohydrate precursors like lactate, glycerol, and amino acids (e.g., alanine).
Explanation: This process occurs mainly in the liver and helps maintain blood glucose levels during fasting or low carbohydrate intake. It is crucial for tissues like the brain and red blood cells that depend on glucose as their primary energy source.

Name two key enzymes unique to gluconeogenesis.

Answer: Pyruvate carboxylase and glucose-6-phosphatase.
Explanation: Pyruvate carboxylase converts pyruvate to oxaloacetate, bypassing an irreversible step of glycolysis. Glucose-6-phosphatase removes phosphate from glucose-6-phosphate to produce free glucose, which can be released into the bloodstream.

What happens to lactate in the Cori cycle?

Answer: In the Cori cycle, lactate produced in the muscles during anaerobic respiration is transported to the liver, where it is oxidized back to pyruvate. Pyruvate is then used in gluconeogenesis to produce glucose, which can be returned to muscles for energy.
Explanation: This cycle prevents lactate accumulation in muscles, which can cause cramps, and efficiently recycles lactate to maintain energy balance during strenuous activities.

How does insulin affect gluconeogenesis?

Answer: Insulin inhibits gluconeogenesis by suppressing the expression and activity of key gluconeogenic enzymes such as PEPCK (phosphoenolpyruvate carboxykinase) and glucose-6-phosphatase.
Explanation: Insulin promotes glycolysis (glucose breakdown) and storage of glucose as glycogen, reducing the need for gluconeogenesis. This regulation ensures balanced glucose levels in the body.

What is the role of glucocorticoids in gluconeogenesis?

Answer: Glucocorticoids stimulate gluconeogenesis by inducing the synthesis of gluconeogenic enzymes (e.g., PEPCK) and promoting muscle protein degradation to provide amino acids as substrates.
Explanation: These hormones are released during stress and increase blood glucose levels to meet the energy demands of the body. Prolonged glucocorticoid activity can lead to elevated blood glucose levels and muscle weakness.