Sesh 4- Energy Storage

Question 1

List 4 types of cells that have an absolute requirement for glucose

Answer 1

1. Red blood cells
2. Neutrophils
3. Cells in lens of eye
4. Innermost cells of renal medulla

Question 2

Where is glycogen stored?

Answer 2

As granules in skeletal muscle and the liver

Question 3

What is the purpose of glycogen in the liver?

Answer 3

Can be mobilised to maintain blood glucose levels

Question 4

What is the purpose of glycogen in skeletal muscle?

Answer 4

Can enter glycolysis in muscle, to generate ATP for muscle contraction

Question 5

Why can’t glycogen stored in skeletal muscle be mobilised to help maintain plasma glucose levels?

Answer 5

Muscles lacks glucose-6-phosphatase that converts G-6-P to glucose

Question 6

Give 2 reasons why glycogen’s branched structure is advantageous

Answer 6

1. Less osmotic effect as stored as 1 molecule

2. Lots of places for enzymes to act for quick glucose release

Question 7

What does phosphoglucomutase do?

Answer 7

Converts G-6-P to G-1-P in the 2nd step of glycogenesis

Question 8

Which 2 enzymes catalyse the final step of glycogenesis?

Answer 8

1. Branching enzyme forms alpha-1,6, bonds

2. Glycogen synthase forms alpha-1,4 bonds

Question 9

What are the 2 enzymes involved in the first step of glycogenolysis?

Answer 9

1. Debranching enzyme

2. Glycogen phosphorylase

Question 10

What effect does glucagon have on the enzymes involved in glycogen metabolism?

Answer 10

Phosphorylates enzymes which…

• reduces glycogen synthase activity
• increases glycogen phosphorylase activity

Question 11

What effect does insulin have on the enzymes involved in glycogen metabolism?

Answer 11

Dephosphorylates enzymes which…

• increases glycogen synthase activity
• reduces glycogen phosphorylase activity

Question 12

What effect does glucagon have on muscle glycogen stores?

Answer 12

None, as muscle doesn’t have glucagon receptors.

Question 13

How is muscle glycogen phosphorylase activated?

Answer 13

Allosterically by AMP

Question 14

What is von Gierke’s disease?

Answer 14

• Congenital deficiency of glucose-6-phosphatase

- Cannot convert G-6-P from liver to glucose, so get hepatomegaly

Question 15

What is McArdle disease?

Answer 15

• Congenital deficiency in muscle glycogen phosphorylase

- Can’t mobilise glucose from muscle glycogen, so present with sever lethargy

Question 16

Roughly how long after fasting does gluconeogenesis kick in?

Answer 16

8 hrs, once liver glycogen stores have been depleted

Question 17

Name the 2 places gluconeogenesis can occur

Answer 17

1. Liver (mainly)

2. Renal cortex

Question 18

What are the 3 major precursors for gluconeogenesis?

Answer 18

1. Lactate
2. Glycerol
3. Amino acids (mainly alanine)

Question 19

What is the role of PEPCK in gluconeogenesis?

Answer 19

Converts oxaloacetate to PEP in 1st stage

Question 20

What is the role of fructose 1,6, bisphosphatase in gluconeogenesis?

Answer 20

Converts fructose 1,6-bisphosphate to fructose-6-phosphate

Question 21

What is the role of glucose-6-phosphatase in gluconeogenesis?

Answer 21

Converts G-6-P to glucose in final step

Question 22

Which 2 enzymes are the major control points of gluconeogenesis?

Answer 22

1. PEPCK

2. Fructose-1,6 bisphosphatase

Question 23

What are the effects of glucagon and cortisol on gluconeogenesis?

Answer 23

Both stimulate it by:

• Increasing amount of PEPCK
• Increasing amount and activity of fructose-1,6-bisphosphatase

Question 24

What are the effects of insulin on gluconeogenesis?

Answer 24

Inhibits it by:

• Reducing amount of PEPCK
• Reducing amount and activity of fructose-1,6-bisphosphatase

Question 25

How long after feeding would glycogenolysis occur?

Answer 25

Between 2 and 10 hrs

Question 26

Do adipocytes increase in size or number first when having to store excess lipid?

Answer 26

Size

Question 27

Which hormone is released by adipocytes that signals the status of fat stores?

Answer 27

Leptin

Question 28

Where is the main site of lipogenesis?

Answer 28

The liver

Question 29

What is the key regulatory enzyme of lipogenesis and what does it do?

Answer 29

Acetyl CoA carboxylase catalyses conversion of acetyl Co A to malonyl CoA.

Question 30

What effect does insulin have on acetyl CoA carboxylase activity?

Answer 30

De-phosphorylates it to increase its activity (i.e. stimulates lipogenesis)

Question 31

What effect does citrate have on acetyl CoA carboxylase?

Answer 31

Allosterically stimulates it

Question 32

What is the importance of malate shuttling in lipogenesis?

Answer 32

Produces NADPH needed to protect against oxidative stress and to provide fatty acid synthase complex with reducing power.

Question 33

Where in the cell does lipogenesis occur?

Answer 33

Cytosol

Question 34

Does beta oxidation of fatty acids or fatty acid synthesis require a higher input of ATP?

Answer 34

Fatty acid synthesis (beta oxidation only needs small amounts of ATP to activate fatty acids)

Question 35

How much TAG is normally stored in a 70Kg man?

Answer 35

15 Kg

Question 36

Where is the most glycogen in the body stored?

Answer 36

``` Skeletal muscle (300g) NB: Liver only stores ~100g ```