Fat/Lipid synthesis

Question 1

Linolenic acid structure

Answer 1

18:3 (9,12,15)

Question 2

Arachidonic acid structure

Answer 2

20:4 (5,8,11,14)

Question 3

Triacylglycerol (TAG)

Answer 3

-Storage of energy
- Physiological fat
- 1st Carbon: saturated fat
2nd carbon: unsaturated fat
3rd: saturated or unsaturated fat

Question 4

Acetyl-CoA Carboxylase (ACC)

Answer 4

-Fatty acid biosynthesis, cytoplasm
Overall: 7 Acetyl CoA + 7 CO2 + 7 ATP –> 7 Malonyl-CoA + 7 ADP + 7 Pi

• Synthesis of palmitate
• Rate-limiting step, irreversible
• ACC has a biotin arm (attached to biotin carrier protein in ACC through lysine) which uses the energy of the ATP to attach to CO2. Then acetyl CoA nucleophilic attacks CO2 to make malonyl CoA

-regulation
Downregulated by glucagon (PKA), adrenaline (PKA), palmitoyl-COA, AMPK (TAMP)
Upregulated by insulin (PP), citrate
-MalonylCoA inhibits FA transport for degradation

Question 5

Fatty acid synthase (FAS)

Answer 5

• Fatty acid biosynthesis , cytoplasm
• (Complex of many enzymatic activities (6)in one protein + an acyl carrier protein ) x2 –> dimer (two multi reaction chamber)

Contains 6 enzymes: MAT, KS, KR, ER, DH, TE

ACP attaches to the PPE part of coenzyme a. It is the SH of PPE that covalently attaches to acetyl CoA

Question 6

ATP-citrate lyase

Answer 6

• Breakdown of citrate into Acetyl CoA for FA synthesis (only citrate can be transported into the mitochondria)
• Citrate + CoA + ATP –> OAA + Acetyl-CoA+ ADP + Pi
• OAA is then transformed into malate. Malate is transformed into pyruvate with malic enzyme. There is production of 1NADPH, and pyruvate an go back into the mitochondria

Question 7

Biotin carboxylase

Answer 7

attached to biotin
- Biotin + CO2 + ATP –> Biotin-CO2 + ADP + Pi.

Then the biotin carrier protein swings the Biotin-CO2 into the transcarboxylase component of ACC

Question 8

Transcarboxylase

Answer 8

Acetyl CoA+ CO2 (from biotin) –> Malonyl CoA

Question 9

Malonyl-Acetyl-CoA-ACP transacetylase (MAT)

Answer 9

1st reaction of FAS for FA synthesis

1- acetyl CoA +ACP-SH –> Acetyl-ACP + CoA-SH

2- Malonyl-CoA + ACP-SH –> Malonyl-ACP + CoA-SH

Question 10

ß-Ketoacyl-ACP-synthase (KS)

Answer 10

2nd step in FAS for FA synthesis

1- acetyl-ACP + KS –> Acetyl-KS + ACP-SH
2- acetyl-KS + malonyl-ACP –> Acetoacetyl-ACP + CO2 + KS

Condensation reaction

Question 11

ß-ketoacyl-ACP reductase (KR)

Answer 11

3rd step of FAS for FA synthesis.

Acetoacetyl-ACP + NADPH + H+ –> D-Hydroxybutyryl-ACP + NADP

reduction step

Question 12

ß-hydroxyacyl-ACP dehydrase (DH)

Answer 12

-4th step in FAS for FA synthesis.

D-ß-Hydroxybutyryl-ACP –> å,ß-trans-butenoyl-ACP + H2O

dehydration step

Question 13

Enoyl-ACP reductase (ER)

Answer 13

å,ß-trans-butenoyl-ACP + NADPH + H+ –> bytyryl-ACP + NADP

reduction step

*use the product 7 times in order to make palmitoyl-ACP

Question 14

Palmitoylthioesterase (TE)

Answer 14

Palmitoyl-acp +water–> palmitate

Question 15

Overall reqction for palmitate synthesis

Answer 15

8 Acetyl CoA

Question 16

Linoleic acid structure

Answer 16

18:2 (9,12)

Question 17

Overall reaction for palmitate synthesis

Answer 17

8Acetyl CoA + 7ATP + 14 NADPH + 14H+–> 6 H2O + 14 NADP + 7ADP + 7 Pi+ palmitate + 8CoA

Question 18

Thiokinase

Answer 18

Palmitate + ATP –” Palmitoyl-CoA (is a thioester)+ AMP + PPi

Can be:

• Stored as TAG
• used for energy
• derivatized: elongated or desaturated

Question 19

3-ketoacyl-CoA synthase

Answer 19

1st reaction in microsomal (Smooth ER) elongation (Major): fatty acid elongation (n+2)

Acyl-CoA (10C and more, sat. or unsat.) + Malonyl CoA –> 3-Ketoacyl-CoA + CoA-SH + CO2

-Condensation reaction.

Question 20

3-Ketoacyl-CoA reductase

Answer 20

2nd reaction in microsomal elongation

3-D-Ketoacyl-CoA + NADPH + H+ –>3-Hydroxyacyl-CoA + NADP

-Reduction reaction

Question 21

3-Hydroxyacyl-CoA dehydrase

Answer 21

3rd reaction in microsomal elongation

3-Hydroxyacyl-CoA –> 2-trans-enoyl-CoA + H2O

-Dehydration reaction

Question 22

2-trans-enoyl-CoA reductase

Answer 22

2-trans-enoyl-CoA + NADPH + H+ –> Acyl-Coa(n+2)

Question 23

thiolase

Answer 23

1st step in mitochondrial elongation : fatty acid elongation (Minor pathway)

Acyl-CoA + Acetyl CoA –> ß-ketoacylCoA + CoA-SH

Question 24

3-L-hydroxyacyl-CoA dehydrogenase

Answer 24

2nd step in mitochondrial elongation

ß-ketoacyl-CoA + NADH + H+ –> L-ß-hydroxyacyl CoA + NAD

-reduction reaction

Question 25

Enoyl-CoA hydratase

Answer 25

3rd step in mitochondrial elongation L-ß-hydroxyacyl CoA --> a,ß-trans-Enoyl-CoA + H2O -Dehydration reaction

Question 26

Enoyl-CoA reductase

Answer 26

4th step in mitochondrial elongation a,ß-trans-enoyl-CoA + NADPH + H+ --> Acyl-CoA (n+2) + NADP -Reduction reaction

Question 27

Generic desaturation of FA in the ER (microsomal) | conditions

Answer 27

Humans have 4 desaturases (give e- to form H2O): ∆9,∆6,∆5,∆4 (count carbonyl as C1) - y = 7,4,3,2 (must be saturated) (don't count carbonyl as C1) - X > or = 5C (can be sat. or unsat.) (don't count last CH3*) - Spacing between 2 double bonds (n+3) *for x and y , count only CH2

Question 28

Glycerol-P dehydrogenase

Answer 28

1st step TAG synthesis in liver and adipose tissue -Dihydrocyacetone phosphate + NADH --> Glycerol phosphate

Question 29

Glycerol kinase

Answer 29

1st step TAG synthesis in liver only Glycerol + ATP --> Glycerol phosphate + ADP

Question 30

Acyltransferase

Answer 30

2n, 3rd and 5th reaction of TAG synthesis 2nd: Glycerol phosphate + Acyl-CoA (sat.) --> lysophosphatidic acid + CoA-SH 3rd: Lysophosphatidic acid + Acyl-CoA (unsat.) --> phosphatidic acid (DAG phosphate) + CoASH 5th: Diacylglycero (DAG) + Acyl-CoA --> Triacylglycerol (TAG) + CoA-SH

Question 31

phosphatase

Answer 31

4th reaction of TAG synthesis Phosphatidic acid + H2O --> Diacylglycerol (DAG) + Pi

Question 32

Carnitine palmitoyl-transferase I

Answer 32

-Fatty acid transport into mitonchondria matrix fatty acyl CoA + Carnitine --> fattyacyl-carnitine + CoA -reaction in imm

Question 33

Carnitine palmitoyl-transferase II

Answer 33

-Fatty acid transport into the mitochondrial matrix fattyacyl-carnitine + CoA --> Fattyacyl-CoA + carnitine -reaction in matrix

Question 34

fatty acyl CoA synthetase

Answer 34

Fatty acid + ATP --> Fatty acyl CoA + AMP + PPi

Question 35

Acyl-CoA dehydrogenase (AD)

Answer 35

1st reaction of ß-oxidation of fatty acid (occurs in mitochondria) Fatty acyl-CoA + FAD --> 2-trans-enoyl-CoA + FADH2 *FADH2 electrons transfered to ETC for production of 2ATP

Question 36

Enoyl-CoA hydratase

Answer 36

2nd step in ß-oxidation of fatty acid 2-trans enoyl CoA + H2O --> 3-hydroxyacyl-CoA

Question 37

3-Hydroxyacyl CoA dehydrogenase

Answer 37

3rd step in ß-oxidation of fatty acids 3-L-hydroxyacyl-CoA + NAD --> 3-ketoacyl -CoA + NADH + H+ - NADH later used in ETC: produces 3 ATP

Question 38

ß-ketoacyl CoA thiolase

Answer 38

3-ketoacyl-CoA + CoA --> acyl-CoA (n-2) + acetyl-CoA - In odd chain FA degradation, the very end product is propionyl CoA (3C) - Each acetyl CoA provides 12 ATP through the TCA cycle

Question 39

Summary of the energy yield from the oxidation of palmitoylCoA

Answer 39

14 ATP (from 7FADH2) + 21 ATP (from 7NADH2) + 96 ATP (from 8 acetylCoA) = 131 ATP - 2ATP (for palmitate--> palmitoyl CoA) = 129ATP

Question 40

propionyl-CoA carboxylase

Answer 40

1st Step for conversion into succinyl-CoA Propionyl-CoA + HCO3 (biotin) + ATP --> D-Methylmalonyl-CoA + ADP + Pi

Question 41

methylmalonyl-CoA epimerase

Answer 41

2nd step for conversion into succnyl-CoA D-Methylmalonyl-CoA L-methylmalonyl-CoA

Question 42

Methyl-malonyl-CoA mutase

Answer 42

3rd step for conversion into succinyl-CoA L-Methylmalonyl-CoA + coenzyme B12 succinyl-CoA succinyl CoA later transformed into OAA then glucose.

Question 43

Enoyl-CoA isomerase

Answer 43

Degradation of fatty acid with 3,4 C=C bond obstacle (because only 2,3 trans double bond can be used for ß-oxidation) 3,4 fatty acyl --> 2,3 trans fatty acyl ==> ßoxidation

Question 44

2,4-dienoyl-Coa reductase

Answer 44

Degradation of FA with 4,5 C=C bond obstacle (1st: 4,5 C=C fatty acyl + FAD --> 2,4 dienoyl fatty acid (2 db) + FADH2) 2nd: 2,4 dienoyl fatty acyl + NADPH + H+ --> 2,3enoyl fatty acyl + NADP

Question 45

3,2-enoyl-CoA isomerase

Answer 45

3,2-enoyl fattyacyl --> 2,3 trans fattyacyl ==> ß-oxidation