MEH Energy Storage - Glycogen and Fat

Question 1

Why can’t glucose get into the brain when it is below a certain level in plasma? How does the body prevent low blood glucose occurring during starvation?

Answer 1

Because when Glucose conc falls below the Km value of the brain transporter then flu cannot get into the brain –> coma

Store of glycogen

Question 2

What is glycation of Hb and how can it be used clinically? Is it enzyme dependent?

Answer 2

Glucose attached to Hb - used as a clinical marker for diabetes - Hba1C

Question 3

What is glycogen - what is it’s structure. How and where is glycogen stored?

Answer 3

As granules in the liver and muscle.

Polymer consisting of chains and branches of glucose residues linked with alpha 1,4 and 1,6 glycosidic bonds

Question 4

What is glycogenin?

Answer 4

A protein that forms a dimer in the centre of a glycogen molecule

Question 5

What main enzyme is responsible for glycogen synthesis vs glycogenolysis? Are they reverse reactions?

Answer 5

Glycogen synthase

Glycogen phosphorylase

Question 6

Does synthesis of glycogen require energy?

Answer 6

Yes

Question 7

What happens to glucose 6 phosphate once glycogen has broken down in muscle vs liver? Why is it different?

Answer 7

Muscle - straight to glycolysis
Liver - can form glucose release glucose into blood for use by other tissues

Muscle lacks G6P (Glucose 6 phosphatase) so cannot produce glucose - liver has it.

Question 8

Which is the better buffer for blood glucose - liver or muscle and why?

Answer 8

Liver - as it has G6P so can convert glucose 6 P to glucose and release into blood

Question 9

What is the effect of glucagon/adrenaline and insulin on glycogen synthase and phosphorylase? Is it the same for liver and muscle?

Answer 9

Glucagon/adrenaline - increases glycogen phosphorylase inhibits glycogen synthase

Insulin - decreases glycogen phosphorylase, increases glycogen synthase

Muscle is different as glucagon has no effect

Question 10

Apart from being modulated by hormones, how else can glycogen synthesis/metabolism be modulated?

Answer 10

By AMP - allosteric modulator of muscle enzyme glycogen phosphorylase. Not of the liver form of the enzyme

Question 11

After 8 hours starvation what occurs to get glucose in the body?

Answer 11

Gluconeogensis

Question 12

What precursors for gluconeogensis are there?

Answer 12

Lactate
Glycerol - released from adipose on breakdown of triglycerides 
Amino Acids 
Pyruvate
G6P from glycogen breakdown in the liver

Question 13

Where does lactate come from for gluconeogenesis (2)

Answer 13

Exercising muscle - anaerobic respiration

RBC - Cori Cycle

Question 14

Which kind of amino acids can be precursors for gluconeogenesis? What are the other types of amino acids?

Answer 14

Glucogenic

Ketogenic

Question 15

Which is the most common amino acid used in gluconeogenesis?

Answer 15

Alanine

Question 16

Where does gluconeogenesis occur (2)?

Answer 16

Liver mainly

Also kidney cortex

Question 17

Why are the 3 main enzymes for gluconeogenesis?

Answer 17

1) G6P
2) Fructose 1,6 bisphosphatase
3) PEPCK

Question 18

Which of the enzymes for gluconeogensis bypasses the irreversible step of glycolysis?

Answer 18

PEPCK

Question 19

Which two of the enzymes are hormonally regulated?

Answer 19

PEPCK

Fructose 1,6 bisphosphatase

Question 20

What effect does Glucagon/Cortisol, and insulin have on PEPCK and F1,6BP?

Answer 20

Glucagon and cortisol - increase enzyme/activity

Insuline - inhibits enzyme/activity

Question 21

What two functions do adipocytes have?

Answer 21

Store TAGs

Leptin - endocrine function

Question 22

What are the main steps of lipogenesis? Say the main regulatory enzyme and what energy is used. Where are lipids made?

Answer 22

1) Glucose - major source of carbon skeleton
2) Glycolysis in cytosol —> pyruvate
3) Pyruvate enters mitochondria and forms acetyl co A and OAA (oxaloacetate)
4) AcoA and OAA form citrate in mitochondria
5) Citrate leaves mitochondria and is broken down into AcoA and OAA again
6) Acetyl co A –> malonyl co A (Acetyl co A carboxylase)
7) Malonyl co A enters the FA synthase complex - FA are build by adding 2C from malonyl co A
8) ATP and NADPH required (NADPH from pentose phosphate pathway or malate shuttle)

In the liver

Question 23

How is lipogenesis regulated?

Answer 23

Acetyl co A carboxylase is regulated by:

Glucagon/adrenaline–> Inhibitory
Insulin/citrate (allosteric) –> Increase lipogenesis

Question 24

How is fatty acid mobilisation regulated (lipolysis)

Answer 24

Hormone sensitive lipase

Glucagon and adrenaline –> increase activity of HSL
Insulin –> inhibition of HSL