Glycogen -gluconeogenesis

Question 1

Differentiate glycogenesis from glycogenolysis

Answer 1

glycogenesis- Synthesis of glycogen from glucose

Glycogenolysis- breakdown of glycogen to form glucose

Question 2

When is liver glycogen broken down?

Answer 2

Broken down between meals and released to maintain blood glucose levels for red blood cells and brain

Question 3

When is muscle glycogen used?

Answer 3

Not available for maintenance of blood glucose levels

Provides energy during bursts of physical activity

Question 4

What is required when hepatic glycogen is depleted?

Answer 4

Gluconeogensis is th eprimary source of glucose overnight

Question 5

Where can glucose residues be added to?

Answer 5

Only be added to an exisitng glycogen chain

Question 6

UDP-glucose acts an an intermediate what is required on this intermediate?

Answer 6

Requires a glycogen ‘primer’ containing at least 4 glucose residues. The primer is covalently attached to a protein called glycogenin

Question 7

What can UDP-glucose be thought as?

Answer 7

An ‘activated’ form of glucose

Question 8

What catalyses the reaction of the formation of UDP-glucose?

Is the reaction reversible?

Answer 8

UDP-glucose pyrophosphorylase

Yes

Question 9

What does glycogen synthase do?

Answer 9

Synthesises glycogen from UDP-glucose- the rate limiting enzyme of glycogenesis

Adds one glucose molecule to glycogen at a time

Question 10

What can glycogen synthase not do?

Answer 10

They can only extend the chains of glycogen meaning they cannot introduce branches or start new molecules

Question 11

Approx every 10 glucose residues what happens to the branching enzyme?

Answer 11

A transglycosylase, introduces alpha 1-6 glycosidic branches into glycogen

Question 12

In glycogenesis: After a hyperglyceamia stimuli occurs what is the hormone and effect that is activated after the high levels of glucose?

Answer 12

Hormone- Insulin (pancreatic beta cells)

Effect- Activation of insulin receptors

Question 13

In glycogenesis: After hypoglycaemia stimuli occurs what is the hormone and effect that is activated after the low levels of glucose?

Answer 13

Hormone- Glucagon (pancreatic alpha cells)

Effect- Inactivation

Question 14

What is glycogenolysis catalysed by?

Answer 14

Glycogen phosphorylase

Question 15

In glycogenolysis what are the three steps that occur?

Answer 15

• Rate limiting step
• One glucose molecule is cleaved of the ends of glycogen at a time
• glucose-1-phosphate is then converted to glucose-6-phosphate

Question 16

In glycogenolysis what happens in the liver?

Answer 16

Glucose 6-phosphate can be de-phosphorylated and the resulting glucose released into the blood stream

Question 17

In glycogenolysis what happens in (skeletal) muscle?

Answer 17

In glucose 6-phosphate cannot be de-phosphorylated but instead is used to provide energy via glycolysis and the TCA cycle

Question 18

In glycogenolysis: After hyperglycaemia stimuli occurs what is the hormone and effect that is activated after the high levels of glucose?

Answer 18

Hormone- Insulin (pancreatic Beta cells)

Effect- Inactivation

Question 19

In glycogenolysis: After stress stimuli occurs what si the hormone and effect that is actiavted after?

Answer 19

Hormone- Corisol (adrenal cortex)

Effect- Activation

Question 20

In glycogenolysis: After stress and hyperglycaemia what is the hormone and effect activated after/

Answer 20

Hormone- Adrenaline (adrenal medulla)

Effect- Activation

Question 21

In glycogenolysis: After hyperglycaemia what is the hormone and effect that is activated after?

Answer 21

Hormone- Glucagon (pancreatic alpha cells)

Effect- Activation

Question 22

What happens after prolonged starvation in gluconeogenesis?

Answer 22

New glucose has to be synthesised

Question 23

What is gluconeogenesis?

Answer 23

Synthesis of glucose within the body from non-carbohydrate precursors

Essentially the reverse of glycolysis

Question 24

What are the precursors involved in gluconeogenesis?

Answer 24

Lactate- Synthesised by skeletal muscle under anaerobic conditions

Amino acids- derived from muscle protein by proteolysis

Glycerol- Derived from triglycerides by lipolysis in adipose tissue

Question 25

Where does the energy come from in glyconeogenesis and where is it released from?

Answer 25

From oxidation of fatty acids released from adipose tissue

Question 26

Where does gluconeogenesis occur?

Answer 26

Mainly in the liver, small amounts in the kidneys

Question 27

How many essentially reversible reactions occur in glycolysis?

Answer 27

• Hexokinase
• Phosphofructokinase
• Pyruvate kinase

Question 28

What are the four unique liver enzymes required in gluconeogenesis?

Answer 28

• Glucose-6-phosphatase
• Fructose-1,6-biphosphatase
• PEP carboxykinase

Question 29

How does the gluconeogenesis proceed via the synthesis of oxaloacetate in mitochondria?

Answer 29

the C4 TCA cycle intermediate which accepts acetyl groups

‘anaplerotic reaction’

Question 30

What is the anaplerotic reaction important for?

Answer 30

Important for accepting acetyl groups from fat breakdown

Question 31

Is gluconeogenesis energetically expensive?

Answer 31

Yes

Question 32

What is the cori cycle formed by?

Answer 32

three different organs

Liver, blood and muscle

Question 33

Describe the role of the different components in the cori cycle?

Answer 33

Blood transports lactate to the liver
Liver converts lactate back to glucose
glucose is released into the blood stream
Buys time and shifts metabolic burden from the muscle to other organs