Fat Storage and Transport

Question 1

What are carbohydrates stored as?

What is our bodies long term fat store?

Answer 1

Glycogen

Triglyceride

Question 2

What 2 tissues is fat released from?

What two tissues can be utilised at?

Answer 2

Small intestine and liver

Muscle and adipose tissue

Question 3

Where does fatty acid synthesis occur?

What is it stimulated by?

Answer 3

Cytosol of liver cells

Insulin

Question 4

What two things are fatty acids formed from?

Where does one of these come from?

Answer 4

Acetyl - CoA and NADPH

Acetyl - CoA mainly comes from carbohydrates via the glycolytic pathway.

Question 5

What is the first step in fatty acid synthesis?

Answer 5

Acetyl CoA is converted to malonyl CoA. This is catalysed by acetyl CoA carboxylase (activated by insulin).
Malonly CoA signifies the FED state as it means that the digested food may be turning into fatty acids.

Question 6

What inhibition is vital after fatty acid synthesis?

Answer 6

Malonyl CoA inhibits carnitine transferase and so inhibits the entry of fatty acids into the mitochondrion to prevent the fatty acid being oxidised.

Question 7

After acetyl CoA is converted to malonyl CoA, how does fatty synthesis occur?

Answer 7

Acetyl CoA (2 carbons) and malonyl CoA (3 carbons) combine. One carbon is released as carbon dioxide (3-1 carbons added)

Question 8

What type of enzyme is a fatty acid synthetase?

Answer 8

A dimer

Question 9

What enzyme needs to be added to glycerol and 3 fatty acids to make a triglyceride?

Answer 9

Glycerol phosphate

Question 10

What needs to be added to a triglyceride for it to move out a cell?

Answer 10

Apoproteins

Question 11

What is the structure of a lipoprotein?

What is their main job?

Answer 11

It has an inner core consisting of triglycerides and cholesterol esters.
It has an outer shell which is a single layer of phospholipids, cholesterol and apoproteins.

Main job is for transportation

Question 12

Give 3 points on apoproteins

Answer 12

1. They have a structural role (hydrophilic groups on surface).
2. Recognised by receptors
3. Activates certain enzymes in lipid metabolism

Question 13

Give 3 classes of lipoproteins

Answer 13

1. Chylomicrons - they carry the triglycerides from the small intestine
2. LDL - mainly carries cholesterol
3. HDL - considered good as they carry fatty acids to the liver for excretion

Question 14

Explain the transport of triglycerides in the capillary to the liver (exogenous fat going from small intestine to liver)

Answer 14

TAG initially has one apoprotein attached.
TAG picks up 2 more apoproteins which provided from HDL. This enters the capillary and lipase is here. This breaks down the triglyceride into fatty acids which enter adipose tissue to be stored as TAG and glycerol which is transported to the liver.

Question 15

Explain the transport of endogenous fat (from the liver to the peripheral tissue)

Answer 15

Glycerol is transported to the liver from the capillary. TAG leaves the capillary and attaches to apoproteins and this can then enter the liver. the liver has a B-100 receptor which is one of the apoproteins on the TAG. It can also be taken up by peripheral tissue due to the tissue have this B-100 receptor also.

Question 16

What role does HDL have in lipid transport?

Answer 16

HDL is made by the liver and intestine. It takes cholesterol from the periphery to the small intestine.
There is an enzyme here called LCAT which takes cholesterol into the liver cells, here it is used to make bile acids which then move to the small intestine.

Question 17

Explain how LDL leads to cholesterol synthesis inhibition

Answer 17

LDL particles are taken up by the cell once bound to receptors. Here, they are packed into a lysosome. The cholesterol attached to the LDL enters the nucleus and inhibits enzymes which synthesise cholesterol

Question 18

What are the intermediates formed during cholesterol synthesis?

How do statins affect this?

Answer 18

Acetyl CoA and Acetoacetyl CoA join to form HMG-CoA. This is converted to mevalonate using the HMG-CoA reductase enzyme (rate-determining step). This mevalonate is converted to cholesterol.

Statins block this enzyme working so no cholesterol is made.

Question 19

What do LDL receptors recognise? What occurs due to this?

Answer 19

They recognise B-100. This removes LDL from blood circulation (ultimately decreasing cholesterol synthesis because more LDL will be taken up into the cell which causes cholesterol inhibition).

Question 20

Give some information on lipoprotein a

Answer 20

In plasma in high concentration it is associated with a increased risk of coronary heart disease (by increasing fatty deposits on the capillary walls).
It is related to plasminogen (competes with it).

Question 21

Explain what atherosclerosis is

Answer 21

It is a build up of plaque inside the arteries.
it leads to inflammation and proliferation of smooth muscle in artery walls.
It begins as a fatty streak from accumulation of foam cells (macrophages).

Question 22

What is one problem associated with the accumulation of cholesterol?

Answer 22

high LDL whcih leads to the damage of B100 receptor which then means that LDL can not be recognised