Question 1

Which of the following best describes the typical concentration of fructose 2,6-bisphosphate in cells?

Accepted Answer

$$1 \, \mu M$$

Question 2

Why is the $$K_m of $$glucokinase (hexokinase IV) much higher than that of hexokinase I?

Accepted Answer

Because the liver has a lower supply of glucose and must respond to demand (rate varies over time).

Question 3

Which of the following is a reason why the $$V_{max} of $$glycogen phosphorylase from muscle needs to be greater than that of the liver?

Accepted Answer

To support rapid muscle contraction, which requires high rates of glycogen breakdown.

Question 4

What is a second reason why muscle glycogen phosphorylase has a higher $$V_{max}$$ than liver glycogen phosphorylase?

Accepted Answer

To maintain blood glucose levels during periods of fasting.

Question 5

If a patient has a mutation that decreases the $$K_m of $$glucokinase in the liver, what is the most likely physiological consequence?

Accepted Answer

Increased risk of hypoglycemia due to excessive glucose uptake by the liver.

Question 6

Which enzyme is primarily responsible for regulating the rate of glycolysis in response to changes in fructose 2,6-bisphosphate concentration?

Accepted Answer

Phosphofructokinase-1 (PFK-1)

Question 7

A sudden increase in muscle activity leads to rapid glycogen breakdown. Which property of muscle glycogen phosphorylase allows this response?

Accepted Answer

High $$V_{max}$$ enables rapid conversion of glycogen to glucose-1-phosphate.

Question 8

Which of the following best explains why the liver must regulate glucose uptake differently than muscle tissue?

Accepted Answer

The liver must maintain blood glucose homeostasis for the entire body.

Question 9

A researcher measures the activity of hexokinase I and glucokinase in the presence of increasing glucose concentrations. Which enzyme will show a sigmoidal response curve?

Accepted Answer

Glucokinase (hexokinase IV)

Question 10

Which of the following scenarios would most likely result in increased fructose 2,6-bisphosphate levels in liver cells?

Accepted Answer

High insulin and low glucagon levels after a carbohydrate-rich meal.

Question 11

A patient with a deficiency in muscle glycogen phosphorylase would most likely experience which symptom during exercise?

Accepted Answer

Muscle fatigue due to inability to rapidly mobilize glucose from glycogen.

Question 12

Which of the following statements about hexokinase I and glucokinase is correct?

Accepted Answer

Hexokinase I has a lower $$K_m$$ for glucose than glucokinase.

Question 13

During prolonged fasting, which enzyme activity increases in the liver to help maintain blood glucose levels?

Accepted Answer

Glycogen phosphorylase

Question 14

Which of the following is a direct effect of increased fructose 2,6-bisphosphate concentration in hepatocytes?

Accepted Answer

Activation of phosphofructokinase-1, increasing glycolysis.

Glucose and Glycogen Regulation: Key Concepts and Enzyme Kinetics

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