Lipid synthesis Flashcards

1
Q

What molecule is used to add carbons 2 at a time for lipid biosynthesis until palmatic acid is formed?

A

Acetyl CoA

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2
Q

What are the intermediates in the pathway linked to?

A

sulfhydryl group of acyl carrier protein

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3
Q

Citrate lyase

A

Enzyme that converts citrate to oxaloacetate to release an Acetyl CoA

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4
Q

Where does lipid biosynthesis occur?

A

cytosol

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5
Q

Citrate Shuttle

A

Transfers the Acetyl CoA across a membrane from the mitochondrion to the cytosol to be used for lipid synthesis

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6
Q

Sources for NADPH

A

Pentose phosphate pathway and malic enzyme

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7
Q

Production of Malonyl CoA is the 1st rate limiting step of lipid biosynthesis. What enzyme is used?

A

Acetyl CoA carboxylase.

This is an irreversible reaction

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8
Q

What activates Acetyl CoA Carboxylase? What inhibits it?

A

Activates: citrate
Inhibits: epinephrine, glucagon, and palmatic acid

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9
Q

What does Malonyl CoA block?

A

Beta oxidation carnitine shuttle

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10
Q

Fatty Acid Synthase

A

Multi-enzyme complex used in lipid biosynthesis

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11
Q

What piece of the FAS is the acetyl substrate from acetyl CoA added to? Which piece catalyzes the reaction?

A

Added to KS. Catalyzed by AT

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12
Q

What piece of the FAS is the malonyl substrate from malonyl CoA added to? Which piece catalyzes the reaction?

A

Added to ACP

Catalyzed by MT

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13
Q

5 steps of fatty acid synthase

A
  1. condensation: (catalyst KS) loss of CO2 from malonyl and transfers 2 carbons from acetyl CoA to malonyl ACP
  2. reduction: (catalyst KR) carbonyl at C3 is reduced using NADPH
  3. dehydration: (catalyst HD) loss of water introduces C2-C3 double bond
  4. reduction: (catalyst ER) reduce double bond using NADPH. Forms 4 carbon fatty acid [completes one pass of the fatty acid]
  5. translocation: transfer of butyryl group from ACP to KS
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14
Q

net reaction for fatty acid synthesis:

8 Acetyl CoA + 7 ATP + 14 NADPH + 14 H

A

1 palmatate + 8 CoA + 7 ADP + 7 Pi + 14 NADP + 6 H2O

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15
Q

2 differences between synthesis and elongation

A
  1. location (elongation in endoplasmic reticulum, synthesis in cytosol)
  2. carrier is CoA
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16
Q

What type of bond does desaturation produce? What catalyzes this reaction?

A

cis double bonds; desaturase

17
Q

What is the rate limiting step of cholesterol synthesis?

A

Formation of mevalonate from 3 Acetyl CoA

18
Q

4 steps of cholesterol synthesis

A
  1. decarboxylation
  2. dephosphorylate
  3. connect all 6 isoprene units
  4. cyclize the chain
19
Q

Where is mevalonate formed?

A

cytosol and ER

20
Q

What is the storage form of cholesterol?

A

Fatty acid is attached to produce a cholesteryl ester

21
Q

What inhibits cholesterol synthesis?

A

High levels of ingested cholesterol. Inhibits HMG CoA reductase

22
Q

What are statins?

A

Competitive inhibitors for the reactive site where HMG CoA binds

23
Q

What molecule does triacylglycerol and phospholipid synthesis begin with?

A

Glycerol-3-phosphate

24
Q

steps of triacylglycerol and phospholipid synthesis

A
  1. 2 fatty acid additions
  2. dephosphorylation (pathway splitting point)
  3. fatty acid addition
25
Q

CDP-choline pathway

cytidine diphosphate

A

Pathway for synthesis of phosphatidylcholine. Enzyme is CDP-choline-diacylglycerol phosphocholine transferase.
(CDP-choline is “activated” choline)