Lecture 23: FA Synthesis

Question 1

Differences between FA synth. and beta oxidation

Answer 1

1. FAS in cytoplasm, not mito.
2. Reducing equivalents come from NADPH, not FAD/NAD
3. Most carbons are from malonyl-CoA, not acetyl-CoA
4. Acyl-carrier protein used, not CoA
5. Rxns performed by 1 large complex, not individual enzymes

Question 2

Purpose of citrate pyruvate shuttle

Answer 2

Brings acetyl-CoA from mitochondria to cytoplasm and converts NADH into NADPH for FAS (rest from PPP)

Question 3

Citrate-pyruvate cycles for 1 palmitate

Answer 3

8 cycles = 8 acetyl-CoA and 8 NADPH (remaining 6 from PPP) for 1 palmitate

Question 4

FA elongation and desaturation

Answer 4

Alternating elongation/desaturation occurs in the ER to diversify from palmitic acid

Question 5

FA elongation

Answer 5

Uses NADPH, malonyl-CoA similar to FAS but separate enzymes from FAS

Question 6

FA desaturation

Answer 6

Creates cis double bonds; enzymes remove 2 H’s at fixed positions (C4-5, 5-6, 6-7, 9-10)

Question 7

Essential FAs

Answer 7

Humans have no enzymes for FAs with double bonds beyond C9; linoleic and linolenic acid come from diet

Question 8

TAG structure

Answer 8

3 FAs esterified via carboxyls with glycerol backbone hydroxyls. Neutral fats that can be solid or liquid (fat or oil)

Question 9

TAG FA differences by position

Answer 9

1: usually saturated
2: usually unsaturated
3: sat. or unsat.

Question 10

Where does TAG occur in the body?

Answer 10

Primarily in the liver, also adipose/muscle

Question 11

Glycerol for TAG synthesis source

Answer 11

Glycerol-3-P comes from DHAP, or in the liver glycerol kinase phosphorylates glycerol.

Question 12

TAG/FA interorgan transport

Answer 12

The intestine exports chylomicrons, the liver exports VLDLs. Lipoprotein Lipase hydrolyzes TAGs to FAs for uptake by target tissues.

Question 13

Membrane lipid classes

Answer 13

1. Phospholipids
2. Glycolipids
3. Cholesterol

Question 14

Phospholipids

Answer 14

Main membrane lipid w/ glycerol or sphingosine backbone. FA chains at C1/C2 and different C3 groups

Question 15

Glycerophospholipid degradation

Answer 15

Phospholipase hydrolysis of specific ester/phosphodiester bonds:
-P-lipase A1 -> R1
-P-lipase A2 -> R2
-P-lipase C -> P-head group
-P-lipase D -> head group only