Gluconeogenesis

Question 1

Differentiate between Gluconeogenesis and Glycolysis

Answer 1

Glycolysis:
- Converts glucose into pyruvate to produce ATP and NADH for energy.
- occurs in the cytoplasm
- Produces a net gain of energy (ATP and NADH).

Gluconeogenesis:
- Converts pyruvate (or other precursors) back into glucose to maintain blood sugar levels during fasting or intense exercise.
- occurs in the liver and kidney
- Requires energy input (ATP and GTP) to drive the synthesis of glucose.

Question 2

Define Conversion of pyruvate to phosphoenolpyruvate (PEP):

Answer 2

This step involves the enzymes pyruvate carboxylase and phosphoenolpyruvate carboxykinase (PEPCK), bypassing the pyruvate kinase reaction in glycolysis.

• in the mitochondria

Question 3

Define Conversion of fructose 1,6-bisphosphate to fructose 6-phosphate:

Answer 3

This reaction is catalyzed by fructose-1,6-bisphosphatase, bypassing the phosphofructokinase step in glycolysis.

• in the cytoplasm

Question 4

Define Conversion of glucose 6-phosphate to glucose:

Answer 4

This final step uses the enzyme glucose-6-phosphatase, bypassing the hexokinase/glucokinase reaction of glycolysis.

• This enzyme is located in the endoplasmic reticulum of liver and kidney cells.

Question 5

Gluconeogenesis primarily occurs where?

Answer 5

in the liver and kidney, where these bypass enzymes are expressed.

Question 6

how are glucose synthesis (gluconeogenesis) and glucose breakdown (glycolysis) reciprocally regulated?

Answer 6

Meaning that when one pathway is active, the other is suppressed, preventing a futile cycle where both processes occur simultaneously and waste energy;

1. Allosteric Regulation
2. Hormonal Regulation
3. Substrate Availability

Question 7

Define Allosteric Regulation

Answer 7

Key regulatory enzymes in each pathway are sensitive to allosteric effectors like ATP, ADP, AMP, and citrate, which bind to specific sites on the enzyme and influence its activity.

Citrate (product of citric acid cycle or TCA) – if citrate builds up, then TCA is backed up and glycolysis can slow down

Question 8

Define Hormonal control:

Answer 8

Hormones like insulin (stimulates glycolysis) and glucagon (stimulates gluconeogenesis) play a major role in regulating the balance between the two pathways by influencing the expression and activity of key enzymes.

Question 9

What does Hexokinase/Glucokinase do in glycolysis

Answer 9

Converts glucose to glucose-6-phosphate. Inhibited by G6P (feedback inhibition).

Question 10

What does Phosphofructokinase-1 (PFK-1) do in glycolysis

Answer 10

Key regulatory enzyme in glycolysis, activated by AMP and fructose-2,6-bisphosphate, inhibited by ATP and citrate.

Question 11

What does Pyruvate Kinase do in glycolysis

Answer 11

Converts phosphoenolpyruvate to pyruvate, activated by fructose-1,6-bisphosphate, inhibited by ATP.

Question 12

What does Pyruvate Carboxylase do in Gluconeogenesis

Answer 12

Converts pyruvate to oxaloacetate, activated by acetyl-CoA.

Question 13

What does Phosphoenolpyruvate Carboxykinase (PEPCK) do in Gluconeogenesis

Answer 13

Converts oxaloacetate to phosphoenolpyruvate, regulated by glucagon and cortisol.

Question 14

What does Fructose-1,6-bisphosphatase do in Gluconeogenesis

Answer 14

Converts fructose-1,6-bisphosphate to fructose-6-phosphate, activated by citrate and inhibited by AMP and fructose-2,6-bisphosphate.