Gluconeogenesis

Question 1

What is the process of gluconeogenesis?

Answer 1

Synthesize glucose from non-carbohydrate sources.

Question 2

Which enzyme in gluconeogenesis is the rate-limiting enzyme and main control point?

Answer 2

Fructose-1,6-bisphosphatase

(reverses the rate-limiting enzyme of glycolysis, PFK-1)

Question 3

Which enzyme in glycolysis is the rate limiting enzyme and main control point?

Answer 3

PFK-1

Question 4

[Mnemonic]

Pathway Produces Fresh Glucose

(how to remember the four enzymes responsible for gluconeogenesis)

Answer 4

Pathway Produces Fresh Glucose

Pyruvate carboxylase

PEP CK

Fructose 1,6-bisphosphatase

Glucose 6-phosphatase

Question 5

What is the function of the pancreatic hormones insulinandglucagon?

Answer 5

Insulin: lowers blood glucose levels

Glucagon: raises blood glucose levels

Question 6

What are the four enzymes unique to gluconeogenesis?

Answer 6

1. pyruvate carboxylase
2. PEP CK
3. fructose 1,6-bisphosphatase
4. glucose-6-phosphatase

Question 7

Gluconeogenesis is almost the exact reverse of which pathway?

Answer 7

Glycolysis

(Except the three irreversible enzymes of glycolysis are replaced by four enzymes in gluconeogenesis.)

Question 8

Which irreversible glycolytic enzyme does pyruvate carboxylase and PEP CK of gluconeogenesis replace?

Answer 8

Pyruvate kinase

• Pyruvate carboxylase converts pyruvate → oxaloacetate (OAA)
• PEP CK converts OAA → PEP

Question 9

Which irreversible glycolytic enzyme does fructose 1,6-bisphosphatase** of gluconeogenesis** replace?

Answer 9

PFK-1

• Fructose 1,6-bisphosphatase converts fructose 1,6 bisphosphate → fructose-6-phosphate

Question 10

Which irreversible glycolytic enzyme does glucose-6-phosphatase of gluconeogenesis replace?

Answer 10

Hexokinase

• Glucose-6-phosphatase converts glucose-6-phosphate → glucose

Question 11

In gluconeogenesis, where is the enzyme glucose-6-phosphatase found?

Answer 11

ER of liver cells

Question 12

In gluconeogenesis, where is the enzyme pyruvate carboxylase found?

Answer 12

Mitochondria

Question 13

Which two enzymes of gluconeogenesis circumvent the action of pyruvate kinase in glycolysis?

Answer 13

1. pyruvate carboxylase
2. PEP CK

Question 14

For gluconeogenesis, what activates pyruvate carboxylase?

Answer 14

Acetyl co-A produced from β oxidation of fatty acids.

Question 15

Fructose 1, 6-bisphosphatase** is the rate-limiting enzyme of gluconeogenesis and is able to regulate it through allosteric inhibition. Which three molecules activate fructose 1, 6-bisphosphatase?

Answer 15

1. glucagon
2. ATP
3. citrate (high energy intermediate)

(Remember that gluconeogenesis is the almost reverse of glycolysis, so the three molecules that inhibit PFK-1 do the reverse and ACTIVATE fructose 1, 6-bisphosphatase.

Question 16

Where in the body does gluconeogenesis occur?

Answer 16

Liver

Question 17

When are glucagon levels elevated?

Answer 17

During a fast and during exercise.

Glucagon raises blood sugar, so it uses stored glycogen and breaks it down into glucose.

Question 18

Fructose 1, 6-bisphosphatase** is the rate-limiting enzyme of gluconeogenesis and is able to regulate it through allosteric inhibition. Which three molecules inhibit fructose 1, 6-bisphosphatase?

Answer 18

1. insulin
2. AMP
3. F 2,6-bP

(Remember that gluconeogenesis is almost the reverse of glycolysis, so the three molecules that activate PFK-1 do the reverse and INHIBIT fructose 1, 6-bisphosphatase.

Question 19

When are insulin levels elevated?

Answer 19

After a meal.

Insulin lowers blood sugar, so it uses glucose and stores it as glycogen.