Gluconeogenesis

Question 1

What is the only fuel for RBC ?

Answer 1

Glucose

Question 2

What is the site of gluconeogenesis ?

Answer 2

Main site is the liver
Kidneys in extreme starvation

Question 3

What is the role of gluconeogenesis?

Answer 3

To help maintain blood glucose levels so the brain and muscle can extract it.
Glucose is synthesised from non-carbohydrate precursors.

Question 4

What are the main precursors of glucose ?

Answer 4

1. Lactate
2. Amino acids- not leucine or lysine
3. Glycerol- from triglyceride breakdown

Question 5

What are the bypass steps of gluconeogenesis?

Answer 5

1. Pyruvate into Phosphoenolpyruvate
2. Fructose 1,6-phosphate into Fructose 6-phosphate
3. Glucose 6-phosphate into glucose

Question 6

Describe bypass step 1 of gluconeogenesis

Answer 6

1. Carboxylation of pyruvate until Oxaloacetate by enzyme pyruvate carboxylase. Requires ATP.
2. Oxaloacetate into Phosphoenolpyruvate by enzyme Phosphoenolpyruvate carboxykinase. Requires GTP.

Question 7

Why are there 2 PEP carboxykinase enzymes in eukaryotes?

Answer 7

There is a cytosolic form and a mitochondrial form.
It allows the cell to adapt to different precursor sources eg. Is lactate is the precursor then the mitochondrial form is used.
It also helps to balance NADH/NAD+ levels for gluconeogenesis.

Question 8

Describe bypass step 2 of gluconeogenesis

Answer 8

1. Fructose 1,6-phosphate is converted into Fructose 6 phosphate using enzyme Fructose 1,6-bisphosphate

Question 9

Describe bypass step 3 of gluconeogenesis

Answer 9

Glucose 6-phosphate into glucose using enzyme Glucose 6-phosphatase
It occurs in the ER of liver and kidney cells.

Question 10

Why do the brain and skeletal muscle lack the glucose 6-phosphatase enzyme ?

Answer 10

The brain uses glucose only for itself, it does not export it.
The muscle uses glucose for its own local energy needs.

Question 12

What is the Cori cycle ?

Answer 12

Lactate formed by active muscle is converted to glucose by the liver.
It maintains blood glucose levels.
In liver: lactate to pyruvate to glucose
In muscle: glucose to pyruvate to lactate

Question 13

What is the glyoxylate cycle ?

Answer 13

It allows organisms to convert Acetyl-CoA from fatty acid oxidation into succinate which is then converted into malate then Oxaloacetate to then enter gluconeogenesis to be turned into glucose.

Question 14

What is glycogen ?

Answer 14

A large, branched polymer made of many glucose molecules