Brenda - Gluconeogenesis

Question 1

What does gluconeogenesis mean?

Answer 1

Biosynthesis of new glucose

Question 2

List the five primary carbon skeletons used for gluconeogenesis

Answer 2

Pyruvate
Lactate
Glycerol
Alanine
Glutamine

Question 3

List the three places gluconeogenesis occurs

Answer 3

Mainly in the liver

Kidney

Small intestine

Question 4

What are the three irreversible reactions in glycolysis?

Answer 4

Hexokinase

Phosphofructokinase

Pyruvate kinase

Question 5

What is done to the three irreversible reactions in glycolysis during gluconeogenesis?

Answer 5

These 3 irreversible reactions are bypassed in gluconeogenesis

Question 6

How does GNG overcome the irreversible pyruvate kinase reaction
(6)

Answer 6

There is two parts:

Pyruvate is converted into 2 oxaloacetate

This is catalysed by pyruvate carboxylase

This reaction needs ATP (dephosphorylation of ATP occurs)

This reaction needs biotin

Occurs in mitochondrial matrix

Oxaloacetate moves into the cytosol where it is reoxidised into 2 phosphoenolpyruvate

Question 7

What is the first step, part b of GNG, oxaloacetate has been generated?

Answer 7

Oxaloacetate moves into the cytosol where it is reoxidised into 2 phosphoenolpyruvate

Question 8

What must oxaloacetate be converted into in order to leave the mitochondria?
(2)

Answer 8

Oxaloacetate is converted into malate (reduction)

It is then converted back into oxaloacetate

Question 9

How does GNG overcome the second irreversible reaction (phosphofructokinase)

Answer 9

Fructose-1,6-bisphosphate is converted into fructose-6-phosphate

Catalysed by fructose-1,6-bisphosphatase

Question 10

How does GNG overcome the third irreversible reaction (hexokinase)
(2)

Answer 10

Glucose-6-phosphate is converted into glucose

Catalysed by glucose-6-phosphatase

Question 11

What happens to some of the lactate produced in muscle?
(2)

Answer 11

Some enters the liver where it is reoxidised to pyruvate where it can then undergo gluconeogenesis

Cori cycle

Question 12

How do plants and bacteria convert their fatty acids to carbohydrates?

Answer 12

Acetyl-CoA is incorporated into carbohydrates via the glyoxylate cycle

Question 12

How do plants and bacteria convert their fatty acids to carbohydrates?

Answer 12

Acetyl-CoA is incorporated into carbohydrates via the glyoxylate cycle

Question 13

What is animals’ only fat breakdown product for gluconeogenesis?

Answer 13

Glycerol

Question 14

What type of diet can lower gluconeogenesis?

Answer 14

A high carbohydrate diet

Question 15

What type of diet can increase gluconeogenesis?

Answer 15

Fasting or low carbohydrate diet

Question 16

What can strongly inhibit gluconeogenesis and cause hypoglycaemia?

Answer 16

Ethanol strongly inhibits gluconeogenesis

Question 17

In general how do mechanisms inhibit gluconeogenesis?

Answer 17

They cause oxaloacetate to be reduced to malate which makes it unavailable for GN

Question 18

What is the blood glucose resting level?

Answer 18

4-5mM

Question 19

What is blood glucose level after a meal?

Answer 19

8-9mM

Question 20

What happens when blood glucose is high?
(2)

Answer 20

Pancreas reduces glucagon secretion

Pancreas increases insulin secretion

Question 21

What do liver cells do when there is high blood glucose?

Answer 21

Glucose enters liver cells and is stored as glycogen or used for TAG synthesis

Question 22

How does the liver sustain blood glucose levels when fasting?

Answer 22

By degrading glycogen stores

Question 23

How does the pancreas respond to lower glucose levels?

Answer 23

As glucose decreases, insulin secretion is reduced and glucose is taken up by muscle and adipose tissue

Glucagon secretion is increased which accelerates glycogenolysis

Question 24

How does the body react to starvation?
(2)

Answer 24

Fatty acids are mobilised from adipose tissue and oxidised by muscle

In the liver any accumulated acetylCoA is converted to ketone bodies

Question 25

How does the liver keep glucose levels up during starvation?
(2)

Answer 25

By using gluconeogenesis substrates to maintain glucose levels

And by forming ketone bodies

Question 26

What two organs have substantial capacity to oxidise ketone bodies?

Answer 26

Brain
Cardiac muscle

Question 27

Why does the need to use some glucose even in starvation?

Answer 27

To maintain ion gradients for transmission of nerve impulses and for the synthesis of neurotransmitters

Question 28

What affects does hypoglycaemia have on the brain?

Answer 28

ATP production in the brain cells falls

Impairs brain cells electrical activity

Causes a coma