11.b Fatty acid synthesis

Question 1

Fatty acid synthesis = (other word)

Answer 1

Lipogenesis

Question 2

What broadly happens during lipogenesis?

Answer 2

• Storage of surplus energy derived from mainly carbohydrates

It is the stepwise addition of 2-C units from acetyl-CoA following the reverse of the sequence of reactions of beta-oxidation

Question 3

What route is followed with fatty acid synthesis (=lipogenesis) if there is a lot of pyruvate > lot of OAA > citrate > ?
What is invested/yielded in the processes?

Answer 3

1. • Citrate can be shuttled outside of the mitochondria + converted into acetyl-CoA
     
     • Acetyl-CoA is lengthened 2C-wise. NADPH 2x invested in the process.
2. • Side trail: Citrate is converted back into OAA
     
     • Using NADH, OAA is converted back into malate
     • Malate can be converted into pyruvate producing NADPH
     • Pyruvate enters mitochondria and is converted back into OAA

Question 4

C20:4 fatty acid: break down, how much ATP?

Answer 4

-2 ATP act
9 * beta ox = 9 * 4 ATP = 36 ATP
10 Acetyl-CoA = 10 * 10 = 100 ATP
134 ATP
4 double bonds = 1.5 * 4 = -6 ATP
134-6 = 128 ATP

Question 5

C18:3 fatty acid breakdown: how much ATP?

Answer 5

-2 ATP activation
8* beta ox = 84 = 32 ATP
9 Acetyl-CoA = 910 = 90 ATP
120 ATP
3 double bonds = 3*1.5= 4.5 ATP
120 - 4.5 = 115.5

Question 6

C18:3 fatty acid breakdown: how much ATP?

Answer 6

-2 ATP activation
8* beta ox = 84 = 32 ATP
9 Acetyl-CoA = 910 = 90 ATP
120 ATP
3 double bonds = 3*1.5= 4.5 ATP
120 - 4.5 = 115.5

Question 7

Beta-oxidation =
Lipogenesis =

Choose: mitochondria/cytoplasm
But only when…..

Answer 7

Beta-oxidation = Mitochondria
Lipogenesis = Cytoplasm

When enough of the acetyl-CoA source is in the mitochondria to be converted into malate and shuttled out (only source = in mito)

Question 8

Acetyl-CoA recycling for fatty acid synthesis: how does this occur? Energy?

Answer 8

Mito: pyr > acetyl-CoA > citrate >
Cyto: Citrate > acetyl-CoA + OAA (-1 ATPc)
Cyto: OAA > Malate (-NADHc) > pyruvate ( +NADPH)
Mito: pyruvate > OAA (-ATPm)

Total:

-1 ATPc
-1 ATPm
-1 NADHc
+1NADPHc

Question 9

Fatty acid synthesis from Acetyl-CoA: how does this occur? Step 1?

Answer 9

Acetyl-CoA will first be converted into acetyl-ACP. No energy used. This acetyl-CoA will be used as the first building block (C2 blue stone).

Question 10

Fatty acid synthesis from Acetyl-CoA: how does this occur? Step 2?

Answer 10

Then, another Acetyl-CoA comes in. Converted into malonyl-coA (-1ATP).

Question 11

Fatty acid synthesis from Acetyl-CoA: how does this occur? Step 3? Which enzyme helps?

Answer 11

FAS: multiple enzyme with subunits arranges the synthesis

MAlonyl-CoA to aceto-acyl-ACP/keto-acyl ACP (-Co2)

Question 12

Fatty acid synthesis from Acetyl-CoA: how does this occur? Step 4,5, 6, final?

Answer 12

Aceto-acyl-ACP to D-3-hydroxy-but (-1 NADPHc)
To crotonyl -ACP (-H2O)
To butyryl-ACP (-NADPHc)
To fatty acid

Question 13

How much needs to be invested for the first elongation of one AcCoA? and thereafter?

Answer 13

1 ATPc
2 NADPHc

Then, 2 NADPHc per cycle

Question 14

What step happens only the first time acetyl-CoA enters the cycle?

Answer 14

Acetyl-CoA > malonyl-CoA > malonylACP.
After, this acetyl-CoA can directly go to acetyl-ACP to aceto-acetyl ACP.

Question 15

You now have made a fatty acid. You then want to make triglycerides: how is this process called?

Answer 15

Esterification

Question 16

You now have made a fatty acid. What is the first next step?

Answer 16

Fatty acid > acyl CoA (-2 ATP)

Question 17

You now have made a fatty acid. What happens step 2? And then?

Answer 17

DHAP -> glycerol-3-p (-1 NADHc)
From now on, a fatty acyl-CoA is added every time. Leading eventually to the triacylglycerol.