Lipid Synthesis

Question 1

What is the signal and target that tells the cell to perform FA synthesis?

Answer 1

A high NADH/NAD+ ratio inhibits Isocitrate Dehydrogenase which drives citrate toward FA syn.

Question 2

What cleaves citrate into oxaloacetate and acetyl CoA?

Answer 2

citrate lyase

Question 3

What does the malice enzyme do and what is the significance of the reaction?

Answer 3

Converts malate to pyruvate by cleaving a CO2 and forming NADPH. This allows citrate to ultimately be converted into acetyl CoA and pyruvate(onto acetyl CoA) during FA syn.

Question 4

Where does the NADPH come from besides the pyruvate/malate cycle?

Answer 4

The pentose phosphate pathway.

Question 5

What are the two functions of the pyruvate/malate cycle in lipogenesis?

Answer 5

1. Transports acetyl CoA from the mitochondria to the cytosol
2. Malic enzyme generates NADPH to power FA syn

Question 6

What is the key regulatory step in FA syn.?

Answer 6

Aceyl CoA Carboxylase converting acetyl CoA to malonyl CoA.

Question 7

What regulates ACC?

Answer 7

INCREASE:
Citrate allosterically activates
Insulin and Xylulose 5-phosphate increase transcription
Insulin also stim dephosphorylation

DECREASE:
Palmitoyl CoA allosterically inhibits (a product)
Phosphorylation by AMP-PK inhibits
Glucagon-cAMP-PKA-inhibitory phosphorylation

Question 8

How does malonyl CoA inhibit beta-ox.?

Answer 8

By inhibiting Carnitine palmitoyl transferase I (CPT I)

Question 9

What is the reaction sequence in FA syn.?

Answer 9

Bond Formation
Reduction
Dehydration
Reduction

Question 10

What is Fatty Acid Sythase (FAS)?

Answer 10

The first step in FA syn. Has two important sulfur atoms. One from a phophopantetheinyl group linked to a serene and the other from the acyl carrier subunit of FAS on a cysteine.

Question 11

What do the Sulfur atoms on FAS do?

Answer 11

One hold acetyl CoA and is transferred to the growing chain on the other sulfur which then becomes the omega carbon.

Question 12

What are the products on FAS bond formation?

Answer 12

CO2

Question 13

What enzymes catalyze FA syn.?

Answer 13

Solely Fatty Acid Synthase

Question 14

What groups are you adding when you lengthen the FA chain?

Answer 14

First step adds Acetyl CoA with a omega - 1 carboxyl. 2nd the carboxyl is reduced to OH. 3rd is a dehydration to a double bond. 4th is another reduction do a C-C single bond.

Question 15

What do the reduction steps of FA syn. use as a reactant?

Answer 15

NADPH from the pyruvate/malate cycle and the pentose phosphate pathway

Question 16

How is FAS re-loaded to begin a new round of FA syn.?

Answer 16

The growing FA chain is moved from the phosphopantetheinyl to the cysteine.

Question 17

How long does FAS continue to synthesize a fat?

Answer 17

16C to palimitate

Question 18

Where are FAs synthesized to up to 16C?

Answer 18

the cytosol

Question 19

Where are FAs synthesized past 16Cs and what adds instead of Acetyl CoA?

Answer 19

The Endoplasmic Reticulum. Malonyl CoA donates the two carbons and the leto group undergoes the same RDR chain to produce a saturated chain.