Lecture 3

Question 1

true or false; acetyl CoA can be used to synthesize fatty acid if there is a surplus of glucose

Answer 1

true

Question 2

where is acetyl CoA usually resynthesized

Answer 2

liver, adipose tissue, mammary tissue

Question 3

What is acetyl CoA converted when there is a surplus of glucose

Answer 3

maloyl CoA

Question 4

What reaction occurs so that acetyl CoA will be converted to malonyl CoA

Answer 4

Biotin dependent CO2 fixation reaction

Question 5

What is the enzyme for the biotin dependent CO2 fixation reaction

Answer 5

acetyl CoA carboxylase

- biotin is a caofactor

Question 6

where do biosynthetic reaction occur

Answer 6

cytosol

Question 7

What are the two ways in which acetyl CoA can be formed

Answer 7

B oxidation

decarboxylation of pyruvate in the mitochondria

Question 8

How is acetyl CoA transported to the cytoplasm

Answer 8

via the formation of citrate

Question 9

What does acetyl CoA carboxylase consist of

Answer 9

biotin carboxylase
bitoin carrier protein
carboxyl transferase

Question 10

What does biotin catalyze

Answer 10

the transfer of the bicarbonate group to biotin

• the activated CO2 is now covalently bound to biotin, itself bound to its carrier protein via a lysine residue
• the carboxylated biotin transfers the carboxyl group to acetyl-CoA in the carboxyl transferase reaction

Question 11

true or false; Malonyl CoA strongly inhibits the carnitine acyl transferase on the inner mitochondrial membrane

Answer 11

true

Question 12

what is the significance of malonyl CoA from inhibiting carnitine acyl transferase

Answer 12

stops futile cycling of the newly made fatty acids being broken down by B-oxidation

Question 13

What is fatty acid synthase

Answer 13

• is a complex involving multiple subunits surrounding a hollow chamber
• its purpose is to catalyze the addition of 2C to hydrocarbon chain forming fatty acids

Question 14

What happens in stage 1 of fatty acid synthase

Answer 14

1. ) acetyl group transferred from acetyl CoA to ACP
   - thioester bond is formed to a PHOSPHOPANTETHEINE cofactor bound to the protein
2. ) acetyl group then passed to B keto-acyl-S-ACP sythase; where it is linked via a thioester bond to cysteine- SH group
3. ) malonyl CoA is attached to another ACP molecule and the acetyl and malonyl groups are condensed to form acetoacetyl-ACP with loss of CO2

Question 15

What happens during stage 2 in fatty acid synthase

Answer 15

acetoacetyl-ACP now undergoes three reactions:

reduction
dehydration
another reduction
which convert it to buytryl ACP

reducing power used is NADPH

Question 16

What does the central core of the fatty acid synthase comprise of

Answer 16

the ACP forming swinging arm to move the growing fatty acyl chain between each of the enzyme subunits

Question 17

what happens during the elongation step ; stage 3

Answer 17

butyryl ACP can now react with another malonyl ACP to form a 6C B ketoacyl ACP —> hexoyl-ACP

5 further cycles will generate palmitoyl ACP from which the Palmitoyl group is transferred to Co-ASH

Question 18

Where does the elongation of fatty acids longer than 16 carbons occur

Answer 18

mitochondria and ER

- uses acyl-CoA, malonyl CoA, NADPH

Question 19

What controls fatty acid synthesis

Answer 19

largely under hormonal control
- insulin stimulates fatty acid synthesis by stimulating glucose entry into the cells and activating pyruvate dehydrogenase

Question 20

What inhibits acetyl CoA carboxylase

Answer 20

is inhibited by long chain fatty acyl CoAs and synthesis also slows if NADPH is limiting

Question 21

What are the two isoforms of acetyl CoA carboxylase

Answer 21

ACC1

ACC2

Question 22

Where is ACC1 present

Answer 22

in liver and adipose tissue

Question 23

Where is ACC2

Answer 23

isoform found in cardiac and skeletal muscle

Question 24

How are triacylglycerides resythesized

Answer 24

glycerol 3 phosphate accepts acyl chains from acyl CoAs using transferase

Question 25

What is diacylglycerol 3 phosphate

Answer 25

aka phosphatidic acid

intermediate in fat as well as phospholipid biosynthesis

Question 26

What can ceramides (sphingolipids) react with

Answer 26

1. ) choline to yield sphingomyelin
2. ) sugars to yield cerebrosides
3. ) sugars and sialic acid to yield gangliosides

Question 27

What are used in the biosynthesis of phosphoacylglycerol

Answer 27

phosphatidyl serine

phosphatidylethanolamine