Fatty Acid and Triacylglycerol Metabolism Flashcards Preview

Medical Biochemistry > Fatty Acid and Triacylglycerol Metabolism > Flashcards

Flashcards in Fatty Acid and Triacylglycerol Metabolism Deck (46):
1

What are the two main sites of fatty acid de novo synthesis?

1) Liver after a carbohydrate rich meal
2) Lactating mammary gland

2

What can be achieved by fatty acid de novo synthesis in the liver after a carbohydrate rich meal?

Fatty acid de novo synthesis in the liver reduces the high blood glucose level
after a carbohydrate-rich mean and it also provides fatty acids for eventual
storage in TAGs in fat cells.

3

Which metabolic condition leads to high citrate levels in liver mitochondria?

A high carbohydrate diet leads to increased citrate in liver mitochondria

4

What happens to the citrate in liver mitochondria after a carb rich meal

High citrate levels in liver mitochondria lead to transfer of citrate into the cytosol

5

Describe the cellular location of citrate lyase and describe the irreversible reaction catalyzed by this enzyme.

-Citrate lyase is found in cytosol.
-Citrate and CoA and ATP are the substrates and products are acetyl CoA ,
oxaloacetate , ADP and Pi

6

Describe the cellular location and the reaction catalyzed by the malic enzyme.

-The malic enzyme is found in liver cytosol.
-Malate and NADP+ are substrates and products are pyruvate, CO2 and NADPH

7

What is the dietary precursor to arachidonic acid?

Linoleic acid

8

Biosynthesis of fatty acids most likely occurs in which state?

Well-fed state

9

Where does Acetyl CoA produced in mitochondria come from?

-oxidation of pyruvate (PDH complex)
-Degradation of fatty acids
-Degradation of ketone bodies
-Degradation of amino acids

10

What happens when ATP is high in the mitochondria which causes Acetyl CoA to be converted to citrate?

Isocitrate dehydrogenase is inhibited

11

What is Acetyl CoA converted to for transport in the cytosol?

Citrate

12

Once in the cytosol, what enzyme converts Citrate into Acetyl CoA and Oxaloacetate?

ATP-Citrate lyase

13

Which enzyme produces NADPH in order to be used in Fatty Acid synthesis?

Malic enzyme
(converts malate to pyruvate)

14

Which enzyme catalyzes the first committed step of fatty acid biosynthesis?

Acetyl CoA Carboxylase (ACC)

15

What is the rate-limiting enzyme for fatty acid synthesis?

Acetyl-CoA Carboxylase

16

Which cofactor does Acetyl CoA Carboxylase need?

Biotin

17

Acetyl CoA Carboxylase requires how many ATP molecules per malonyl-coA formed?

1 ATP

18

The enzyme Acetyl CoA Carboxylase converts _____ to _____

Acetyl CoA
Malonyl CoA

19

What two molecules are used in short term allosteric regulation of Acetyl CoA Carboxylase?

Citrate
Palmitoyl CoA

20

How does citrate allosterically regulate Acetyl CoA Carboxylase?

Citrate shifts the polymer - monomer equilibrium towards polymer formation --> activation

21

How does Palmitoyl CoA allosterically regulate Acetyl CoA Carboxylase?

Palmitoyl CoA shifts the equilibrium toward monomer formation --> inhibition

22

What contributes to short term HORMONAL regulation of Acetyl CoA Carboxylase?

Glucagon
Epinephrine
Norepinephrine

23

How do glucagon, epinephrine and norepinephrine act upon Acetyl CoA Carboxylase?

Trigger cAMP dependent phosphorylation of enzyme (through activation of AMPK) that shifts the equilibrium toward monomer formation (inactive form).

24

How does high carb, fat free diet lead to Long term regulation of Acetyl CoA Carboxylase.

Up-regulation/ induction of ACC resulting in increased synthesis of FA

25

How do high-fat diets, fasting ad glucagon levels regulate Acetyl CoA Carboxylase long term?

Lead to decreased synthesis (down regulation, repression) resulting in decreased synthesis of FA

26

Which form of Fatty Acid Synthase is the fully functional form?

Dimeric

27

How does insulin effect Fatty Acid Synthase?

Upregulates the amount of enzyme expressed

28

In the first reaction of FA synthesis, Acetyl CoA is added to a ______ group of which domain of FAS?

Cysteine-SH group;
Condensing Enzyme (CE) domain

29

What is added in the second reaction of FA synthesis?

Malonyl CoA

30

Which group is Malonyl CoA added to in the second step of FA synthesis?

ACP sulfhydryl group
(ACP= acyl carrier peptide)

31

What occurs during the 3rd reaction of FA synthesis?

Acetyl group is transferred to the Malonyl Group with the release of carbon dioxide

32

Regarding the 4th step of FA synthesis, the _______ is _______ to a ______ by the ________ activity.

Keto group;
Reduced;
Hydroxyl group;
Beta-ketoacyl reductase

33

Regarding the 5th reaction, what is dehydrated to form a trans-monounsaturated fatty acyl group?

Beta-hydroxybutyryl-ACP

34

What occurs in the 6th reaction of Fatty Acid synthesis

An acyl group is converted to a butyryl group
Then, butyryl group is transferred from ACP sulfhydryl group to CE sulfhydryl

35

What occurs after step 6 in FA synthesis?

The butyryl group is now ready to condense with a new malonyl group (step 3) to repeat the process

36

Regarding FA Synthesis, Once the fatty acyl group reaches its final carbon chain length, what occurs in step 7?

Thioesterase activity hydrolyses it, forming final free form.

37

What modifications are typically made to produce variety in fatty acids?

-chain elongation to give longer fatty acids
-desaturation, giving unsaturated fatty acids

38

Where does chain elongation of fatty acids primarily occur?

Membranes of ER and involves addition of malonyl CoA to palmitate.

39

Where is the minor elongation pathway of fatty acids and how does it occur?

Mitochondria;
Reversal of B-oxidation.

40

What introduces sites of unsaturation (double bonds) in fatty acids?

Fatty acyl-CoA desaturases

41

In the fatty acid desaturation system, what positions are doubles bonds introduced by fatty acyl-CoA desaturases?

5, 6 or 9

42

Why are linoleate and linolenate considered essential fatty acids?

Because they have unsaturations beyond carbon 9

43

What 3 enzymes are involved in the fatty acid desaturase system (an electron transport system in the ER)

1) cytochrome b5
2) desaturase
3) NADPH-cytochrome b5 reductase

44

What are the substrates in phosphatic acid synthesis?

DHAP--> Glycerol-3-Phosphate --> Monoacylglycerol-3-phosphate---> Phosphatic Acid

45

DHAP is converted to Glycerol-3-phosphate using which enzyme?

Glycerol-3-phosphate

46

What are the substrates of TAG synthesis?

Phosphatic acid --> 1,2-Diacylglycerol--> TAG