Biochem Exam 4: Fatty Acid Synthesis

Front 1

What 2 precursors are necessary for FA synthesis?

Back 1

Acetyl-CoA and malonyl-CoA

Front 2

What is the major source of carbons for FAs?

Back 2

Excess dietary glucose

Front 3

What enzyme catalyzes the synthesis of malonyl-CoA from Acetyl-CoA?

Back 3

Acetyl-CoA carboxylase
(rate limiting enzyme)

*malonyl-CoA is the immediate donor of the two-carbon units

Front 4

What enzyme attacks the growing FA chain to the acyl-carrier protein (ACP) of FAs?

Back 4

Fatty Acid Synthase (FAS)

*each addition followed by 2 reductions using NADPH

Front 5

When the malonyl group combines with the acetyl group (on the ACP, initially from an acetyl-CoA ) via FAS, what is formed and what is released?

Back 5

a 3-ketoacyl group is formed

CO2 is released

Front 6

Where are FAs produced in humans?

Back 6

in liver

*FAs cannot be synthesized and degraded at same time

Front 7

Where does the NADP* used for FA synthesis come from?
What enzyme is dependent on NADP+?

Back 7

pentose-P pathway

Malic enzyme, converts it to NADPH

Front 8

In the cytosol, citrate is cleaved into acetyl-CoA and OAA by what enzyme?

What does this enzyme require?
What activates it?

Back 8

citrate lyase (citrate cleavage enzyme)

requires ATP
activated be insulin

Front 9

When acetyl-CoA is (high/low) PDH is inhibited and pyruvate carboxylase is activated.

Back 9

high

Front 10

In the presence of NADH, OAA is reduced to malate via what enzyme?

Back 10

cystolic malate dehydrogenase (NAD+ dependent)

Front 11

Malate is converted to pyruvate via what enzyme?

In this reaction what NADPH is produced and what is released?

Back 11

malic enzyme (decarboxylating or NADP+ dependent malate dehydrogenase)

CO2 released

Front 12

To summarize, what is the fate of citrate in the cytosol?

Back 12

citrate --> OAA & Acetyl CoA (via citrate lyase)
OAA--> Malate (via cystolic malate dehydrogenase)
Malate--> Pyruvate (via malic enzyme)

Front 13

Citrate ---> Acetyl CoA
is stimulated by an increase in insulin or glucagon?

Back 13

insulin, activates PDH by dephosphorylation via PDC phosphatase

Front 14

Insulin also induces synthesis of what 3 enzymes?

Back 14

Malic enzyme
G-6-P dehydrogenase
Citrate Lyase

Front 15

Accumulation, followed by influx into cytosol, of citrate is due to what the inhibition of what enzyme?

Back 15

isocitrate dehydrogenase

Front 16

Conversion of Acetyl-CoA to Malonyl-CoA is done via what enzyme?

What 2 things does this reaction require?

Back 16

Acetyl-CoA carboxylase
***rate limiting enzyme of FA synth

requires Biotin & ATP
(bc carboxylations all use biotin)

Front 17

What are 3 mechanisms of Acetyl-CoA carboxylase regulation?

Back 17

1. phosphorylation
2. allosteric modification
3. induction/repression of its synthesis

Front 18

How does phosphorylation regulate Acetyl-CoA carboxylase?

Back 18

inhibited: AMP-Activated protein kinase (phosphorylated)
activated: dephosphorylation

Front 19

How does allosteric modification regulate Acetyl-CoA carboxylase?

Back 19

inhibited: palmitoyl-CoA
activated: citrate

Front 20

How is Acetyl-CoA carboxylase synthesis regulated?

Back 20

repressed: low insulin/glucagon
induced: high insulin/glucagon

Front 21

A high sugar breakfast activates what enzyme?

Back 21

Acetyl-CoA carboxylase

Front 22

The reduction of a beta-ketoacyl group on the fatty acid synthase complex occurs via what reducing agent?
What is the ketone group reduced to?

Back 22

NADPH is the reducing agent

ketone group reduced to an alcohol

Front 23

During FA synthesis, how is degradation of FAs inhibited?

Back 23

malonyl-CoA that is being produced inhibits CPTI, thus preventing degradation

Front 24

Activated palmitate can be elongate __ carbons at a time. Where does it get these carbons from?
Where does this occur?

Back 24

2 carbons from Malonyl-CoA

in the ER

Front 25

What is the major elongation of Palmitate?

What provides the reducing power?

Back 25

major elongation:
Palmitoyl-CoA (C16) --> Stearyl-CoA (C18)

NADPH provides reducing power

Front 26

Desaturation of FAs occurs where?

What 3 things does it require?

Back 26

occurs in the ER

Requires: molecular oxygen (O2), NADH, & cytochrome B5

Front 27

In order for 500g of sugar to be converted into cystolic Acetyl-CoA, what occurs?

Back 27

insulin is secreted, ATP is consumed

Front 28

What 2 polyunsaturated fats are precursors of eicosanoids?
Other FAs can be converted to form these essential fatty acids or they may be provided by the diet

Back 28

omega 3 & omega 6

Front 29

How is linoleic acid converted to arachidonic acid?

Back 29

1st desaturated at carbon 6
2nd elongated by 2 carbons
3rd desaturated at carbon 4

Front 30

In summary, FA synthesis is catalyzed by 2 tightly regulated enzymes. What are they?

Back 30

acetyl-CoA carboxylase
and
fatty acid synthase