Storage of Carbohydrates as Fat

Question 1

Lipogenesis

Answer 1

synthesis of fatty acids from acetyl CoA

Question 2

where does this usually occur

Answer 2

fat usually stored in adipose tissue, there is some adipose tissue in liver

Question 3

What does acetyl-CoA carboxylase?

Answer 3

• activates acetyl-CoA - which primes for lipogenesis
• Acetyl-CoA fixes with carbon dioxide
• Carboxylation reaction using ATP (CO2 at the end of acetyl-CoA

Question 4

Lipogenesis in terms of reduction/ dehydration

Answer 4

reduction - dehydration - reduction

Question 5

Fatty acid synthesis

Answer 5

1. acetyl and malonyl groups
2. decarboxylating the malonyl
3. catalysing the reaction between the decarboxylated malonyl and growing fatty acid chain
   - Reduction/ dehydration/ reduction
   - releasing as FA-CoA

Question 6

Input and output

Answer 6

• each round of adding 2 C requires NADPH

- Decarboxylase to carboxylase ( uses ATP)

Question 7

Desaturation occur

Answer 7

is done after release

we can make saturated and unsaturated fatty acids

Question 8

Acetyl CoA carboxylase

Answer 8

stimulated by insulin
dephosphorylation
- stimulated by citrate (activates) usually when there is a build up of citrate from the kreb cycle as could be going slower than glycosis
inhibited by long-chain fatty acyl CoA

Question 9

Where does Acetyl- CoA go

Answer 9

• some lost in krebs cycle (carbon atoms fully oxidised to CO2 + lots of NADH produced to generate ATP)
• some go to lipogenesis (moved out into cytoplasm + activated for fat synthesis by formation of malonyl CoA)

Question 10

First step before fate of acetyl -CoA

Answer 10

citrate formation

- condensation of acetyl Co-A with oxaloacetate (regenerates coenzyme A)

Question 11

What happens to citrate once moved into cytoplasm

Answer 11

• citrate is cleaved by ATP-Citrate lyase (ACL)

- using CoA to generate acetyl-CoA and oxaloacetate (requires energy)

Question 12

how does Oxaloacetate generate NADPH

Answer 12

need to return the matrix, otherwise levels would decrease. However it cannot cross the mitochondril membrane , thus is converted to malate and pyruvate, thus generates the reductant NADPH

Question 13

what is NADPH involved in

Answer 13

NADPH is a reductant which is involved in anabolic reactions

Question 14

What pathway produces NADPH

Answer 14

Pentose phosphate pathway - produces NADPH in proportion to the demand of lipogenesis

Question 15

what is the key regulator in Pentose Phosphate pathway

Answer 15

G6PDH

Question 16

What do you with the 5-P at end of the pentose phosphate pathway

Answer 16

back into glycolysis

the 5C react together and exchange chunks of C until eventually they have a pool of C6 and C3

Question 17

Other roles of PPP

Answer 17

• Ribose 6-phosphate is used to make nucleotides (DNA, RNA)
• NADPH is a anti-oxidant (gets rid of free radicals which could damage DNA)
• RBC a deficiency of G6PDH can cause anemia as it would be exposed to free radicals

Question 18

Role of Malonyl CoA

Answer 18

inhibits CAT-I
fatty acid oxidation is inhibited by malonyl CoA
- Insulin stimulates malonyl CoA