Lipid synthesis

Question 1

What is the first step of fatty acid synthesis?

Answer 1

Transport of acetyl CoA to cytosol by the citrate shuttle

Question 2

What is the function of the citrate shuttle?

Answer 2

Transports acetyl CoA and NADPH into the cytosol from the mitochondria

Question 3

When is citrate high?

a) fasted state
b) fed state

Answer 3

b

Question 4

Why can citrate move into the cytosol?

Answer 4

It has a carrier

Question 5

What happens to citrate when it enters the cytosol?

Answer 5

Splits into acetyl CoA and oxaloacetate

Question 6

What is the fate of acetyl CoA from citrate?

Answer 6

Substrate for fatty acid synthesis

Question 7

What is the fate of oxaloacetate from citrate?

Answer 7

Converted to pyruvate and NADPH is made.

Pyruvate enters the mitochondria

Question 8

What is the 2nd step fo fatty acid synthesis?

Answer 8

Activation of acetyl CoA - carboxylation to from malonyl CoA.
Acetyl CoA + CO2 –> Malonyl CoA
(ATP –> ADP)
Acetyl CoA Carboxylase

Question 9

What enzyme catalyses the activation of acetyl CoA?

Answer 9

Acetyl CoA carboxylase

Question 10

What enzyme catalyses the sequential addition of 2 carbon units?

Answer 10

Fatty acid synthase

Question 11

What is the structure of fatty acid synthase?

Answer 11

It is a dimer that contains 2 acyl carrier proteins

Question 12

How does acetyl CoA interact with fatty acid synthase?

Answer 12

Each acyl carrier protein on the fatty acid synthase accepts malonyl CoA and acetyl CoA.
The CoAs are released

Question 13

What happens once the CoAs are released from he fatty acid synthase acyl carrier protein complex?

Answer 13

Acetyl ACP is cleaved off and transferred to malonyl ACP in a condensation reaction. CO2 is released.
This forms acetoacetyl ACP

Question 14

What 3 steps elongate acetoacetyl ACP?

Answer 14

Reduction, dehydration, reduction

Question 15

How does the chain get elongated further?

Answer 15

The elongated chain takes the place of acetyl CoA in the cycle

Question 16

What activates acetyl CoA carboxylase?

Answer 16

Citrate and ATP allosterically, insulin by de-phosphorylation

Question 17

When does fatty acid synthesis stop?

Answer 17

When 16 carbon chain is formed.

Cleaves off ACP and forms palmitate

Question 18

What inhibits acetyl CoA carboxylase?

Answer 18

Palmitate by product feedback.

Glucagon and adrenaline by phosphorylation

Question 19

Where does phosphorylation occur beyond C16?

Answer 19

Endoplasmic reticulum

Question 20

How are double bonds introduced?

Answer 20

Oxidases

Question 21

What is cholesterol a precursor of?

Answer 21

Bile and all steroid hormones

Question 22

How is cholesterol formed and where?

Answer 22

In cytosol.

From HMG using HMG-CoA reductase

Question 23

How are fatty acids transported in the blood stream?

Answer 23

Bound to albumin

Question 24

How are triglycerides and cholesterol transported in the blood stream?

Answer 24

Bound to lipoproteins

Question 25

What are the 5 classes of lipoproteins?

Answer 25

``` Chylomicrons VLDL IDL LDL HDL ```

Question 26

Describe the general structure of lipoproteins?

Answer 26

Phospholipid circle with hydrophobic core and store triglycerides and esterified cholesterol in the centre

Question 27

What is the function of chylomicrons?

Answer 27

Transport triglycerides

Question 28

What do chylomicrons contain?

Answer 28

Triglycerides, cholesterol and apo protein B48

Question 29

What occurs to chylomicrons hone they enter the blood?

Answer 29

HDL donates apo CII and E | This activates lipoprotein lipase not he endothelial surface of vascular system

Question 30

What happens to chylomicrons when triglyceride levels are low?

Answer 30

Return CII and E back to HDL and then go to the liver to be degraded

Question 31

What is the function of VLDL and IDL?

Answer 31

Transport lipids from the liver to the rest of the body

Question 32

Where is VLDL made?

Answer 32

Hepatocytes

Question 33

What do VLDL contain?

Answer 33

TAG, cholesterol and apo100

Question 34

What occurs to VLDL when it enters blood?

Answer 34

HDL donates apo CII and E | Lipoprotein lipase activated, TAG hydrolysed into glycerol and fatty acids

Question 35

How does VLDL become IDL?

Answer 35

TAG is hydrolysed, as they off load TAG become IDL. | CII returned to cholesterol

Question 36

What happens to IDL remaining in circulation?

Answer 36

Receives cholesterol from HDL. Donates phospholipid and ATG in return to become LDL

Question 37

What is the function of LDL?

Answer 37

Transport cholesterol to tissues

Question 38

What happens to LDL in circulation?

Answer 38

Enters cells by endocytosis and fuses with lysosomes to release cholesterol

Question 39

What does HDL contain?

Answer 39

Phospholipids and apo proteins

Question 40

What is the function of HDL?

Answer 40

Accepts free cholesterol from peripheral cells and esterifies it and passes to VLDL, IDL, LDL

Question 41

What causes genetic dyslipidaemias?

Answer 41

Elevated TAG or cholesterol due to abnormal lipid metabolism

Question 42

What causes abnormal lipid metabolism?

Answer 42

Abnormal api-protein, receptors or lipoprotein lipase

Question 43

What do genetic dyslipidaemias cause?

Answer 43

Fatty deposits in artery