Energy Storage, Glycogen & Fat

Question 1

How and where is glucogen stored?

Answer 1

Stored as glycogen granules in:

muscles (provide muscle with energy)

liver (provide plasma glucose)

Question 2

What tissues have an absolute requirement for glucose?

Answer 2

RBCs = no mitochondria

neutrophils,

inner most cell of kidney medulla,

lens of eye

Question 3

Briefly explain the structure of glycogen

Answer 3

α-1-4 glycosidic bonds form chain

α-1-6 glycosidic bonds form branch points, braches can be broken to release energy

Question 4

Describe the major energy stores in a 70kg man.

Answer 4

TAG ~600,000,

muscle protein ~100,000

Question 5

Describe, in outline, the reactions involved in glycogen synthesis: glycogenesis

Answer 5

Glucose –> G6P –> G1P –> UDP-glucose + glycogen residues = glycogen

Question 6

Describe, in outline, the reactions involved in glycogen breakdown: glycogenolysis

Answer 6

Glycogen + Pi –> glycogen + G1P,

G1P to G6P used for muscle energy prod, released by liver as glucose

Question 7

Compare the functions of liver and muscle glycogen

Answer 7

Liver = G6P to glucose, by G6Pase, to blood.

Muscle = no G6Pase, so G6P enters glycolysis for energy prod

Question 8

What enzyme rate limits glycogen synthesis?

Answer 8

Glycogen synthase

Question 9

What enzyme rate limits glycogen degradation?

Answer 9

Glycogen phosphorylase

Question 10

What effect does insulin have on liver glycogen enzymes?

Answer 10

Increase synthase, decrease phosphorylase

Question 11

What effect does glucagon/adrenaline have on liver glycogen enzymes?

Answer 11

Increase phosphorylase, decrease synthase

Question 12

What effect does glucagon have on muscle glycogen stores?

Answer 12

It has no effect

Question 13

Explain the clinical consequences of glycogen storage diseases

Answer 13

Excess = tissue damage.

Low stores = hypoglycaemia/poor exercise tolerance.

Von gierkes disease = G6Pase def = can’t release glycogen stores.

McArdle disease = muscle glycogen phosphorylase def = quick fatigue

Question 14

Explain why and how glucose is produced from non-carbohydrate sources

Answer 14

Gluconeogenesis =

~8 hours, liver glycogen depletes, need alternate source of energy = lactate (anaerobic glycolysis), glycerol (adipose tissue), AA (protein)

Question 15

Name the key enzymes of gluconeogenesis

Answer 15

1) PEPCK,
2) fructose 1,6-bisphosphatase,
3) glucose-6-phosphatase

Question 16

What is gluconeogenesis?

Answer 16

After 8hrs, no liver glycogen = alternate source of glucose required

Met pathway resulting in generation of glucose from non-carb carbon substrates:

1) glycerol
2) lactate
3) glucogenic AA

Question 17

What hormones inhibit and stim gluconeogenesis?

Answer 17

Insulin = inhibits.

Glucagon = stimulates

Question 18

Explain why triacylglycerols can be used as efficient energy storage molecules in adipose tissue

Answer 18

TAG is hydrophobic = stored in anhydrous form in adipose tissue – highly efficient energy store = energy content per gram twice of carb or protein

Question 19

Give an overview of dietary triacylglycerols metabolism

Answer 19

Intestinal epithelial cell absorb TAG to lymph to blood stored in adipose – transported to tissue on albumin = fatty acid oxidation = energy

Question 20

Describe how fatty acid oxidation differs from fatty acid synthesis

Answer 20

Oxidation = remove C2 as acetyl-CoA, in mitochondria, oxidative: prod NADH/FADH2, needs small ATP, insulin inhibits.

Synthesis = add C2 by malonyl CoA, in cytoplasm, reductive: requires NADPH, needs large ATP, insulin stim.

Question 21

What effect does insulin have on glycogen phosphorylase in muscle?

Answer 21

Decrease activity

Question 22

Where does fatty acid synthesis occur?

Answer 22

Cytoplasm

Question 23

What are the benefits of glycogens structure?

Answer 23

1) readily release glucose = breaking many diff points

2) reduce osmotic effect by storing as one molecule

Question 24

What enzyme is involved in glycogenesis?

Answer 24

Glycogen synthase

Question 25

What enzyme is involved in glycogenolysis?

Answer 25

Glycogen phosphorylase

Question 26

What is von Gierkes Disease?

Answer 26

G6Pase def

Hepatomegaly = cant release glycogen stores

Question 27

Outline McArdle disease

Answer 27

Muscle glycogen phosphorylase def

Physically exhausted as cant utilise muscle stores