FA and TG Synthesis

Question 1

Name the 16 carbon FA that we synthesize
16: 4; w-6, where are the double bonds located?
why are phospholipids especially good for the membrane?
Name 3 benefits of short (c4-c10) FA?

Answer 1

Palmitic Acid
at fourth carbon from carbonyl, at 6th carbon from methyl
one of the two FA is unsaturated –> fluidity
Direct absorption into enterocyte, PBC, mitochondria

Question 2

Where Does FA synthesis occur?

What splits long FA chains?

Answer 2

Liver (mostly)

Thioesterase

Question 3

What is the starting substance of FA synthesis. Where is it made? Why is it turned into citrate? How is citrate generated?

Answer 3

Acetyl-CoA, Mitochondrial matrix, AcCoA cannot leave the Matrix, Citrate can,

pyruvate (50-50) some go to pyruvate carboxylase –> oxaloacetate; other pyruvate dehydrogenase complex –> Acetyl CoA; combine together by citrate synthase to form citrate (step 1 of krebs)`

Question 4

Explain how Acetyl-CoA is formed? Full

Answer 4

Glucose –> Pyruvate (cytosol)
Pyruvate –> Acetyl CoA (PDC) - (MATRIX)
Acetyl-CoA –> FA (cytosol)

pyruvate (50-50) some go to pyruvate carboxylase –> oxaloacetate; other pyruvate dehydrogenase complex –> Acetyl CoA; combine together by citrate synthase to form citrate, citrate leaves and is lysed (c.lyase) Acteyl-CoA and oxaloacete

O –> malate –> pyruvate; Acetyl-CoA –> FA synthesis

Question 5

Explain how FA is formed from Acetyl-CoA?

Answer 5

Acetyl-CoA —ACoA Carboxylase –> Malonyl CoA —FA synthase + thioesterase–> palmitate

Question 6

All carboxylase enzymes need what vitamin to work? What enzyme in the process is a carboxylase?

Answer 6

B7 - Biotin

pyruvate carboxylase

Question 7

What is the rate limiting step of FA synthesis? What enzyme?

Answer 7

formation of Malonyl-CoA

Acetyl acid carboxylase

Question 8

What are the allosteric/hormonal regulators of Acetyl CoA carboxylase?

Answer 8

Citrate (+) and FA (-)

Insulin (+): so the active form of Acetyl CoA carboxylase is dephosphorylated

Glyucagon, AMPK (low energy): (-) phosphorylates enzyme (inactive)

Question 9

Fatty acids are stored as ________: explain the enzymatic process by which this occurs. What happens to synthesized TG that have been in the liver for a few days?

Answer 9

TG

packaged in VDL’s

Question 10

Describe TG formation from FA and Glycerol

Answer 10

FA-CoA + [DHAP to Glycerol(P)] = TG

Glycerol is activated to Glycerol phosphate, activated FA are added, stops at two FA for synthesis of phospholipid.

Question 11

Where is Ketone bodies synthesized? What intermediate is also used for Cholesterol synthesis? What is the regulatory enzyme that cleaves this intermediate?
What is the product of cleaving?
What hormone causes synthesis of KB?

Answer 11

Liver
HMG - CoA
HMG - CoA Lyase
acetoacetic acid (KB --> can be degraded further) + Acetyl CoA 
Glucagon