Fatty Acid and Triacylglycerol Metabolism

Question 1

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

Answer 1

1) Liver after a carbohydrate rich meal

2) Lactating mammary gland

Question 2

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

Answer 2

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.

Question 3

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

Answer 3

A high carbohydrate diet leads to increased citrate in liver mitochondria

Question 4

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

Answer 4

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

Question 5

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

Answer 5

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

Question 6

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

Answer 6

• The malic enzyme is found in liver cytosol.

- Malate and NADP+ are substrates and products are pyruvate, CO2 and NADPH

Question 7

What is the dietary precursor to arachidonic acid?

Answer 7

Linoleic acid

Question 8

Biosynthesis of fatty acids most likely occurs in which state?

Answer 8

Well-fed state

Question 9

Where does Acetyl CoA produced in mitochondria come from?

Answer 9

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

Question 10

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

Answer 10

Isocitrate dehydrogenase is inhibited

Question 11

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

Answer 11

Citrate

Question 12

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

Answer 12

ATP-Citrate lyase

Question 13

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

Answer 13

Malic enzyme

converts malate to pyruvate

Question 14

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

Answer 14

Acetyl CoA Carboxylase (ACC)

Question 15

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

Answer 15

Acetyl-CoA Carboxylase

Question 16

Which cofactor does Acetyl CoA Carboxylase need?

Answer 16

Biotin

Question 17

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

Answer 17

1 ATP

Question 18

The enzyme Acetyl CoA Carboxylase converts _____ to _____

Answer 18

Acetyl CoA

Malonyl CoA

Question 19

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

Answer 19

Citrate

Palmitoyl CoA

Question 20

How does citrate allosterically regulate Acetyl CoA Carboxylase?

Answer 20

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

Question 21

How does Palmitoyl CoA allosterically regulate Acetyl CoA Carboxylase?

Answer 21

Palmitoyl CoA shifts the equilibrium toward monomer formation –> inhibition

Question 22

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

Answer 22

Glucagon
Epinephrine
Norepinephrine

Question 23

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

Answer 23

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

Question 24

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

Answer 24

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

Question 25

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

Answer 25

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

Question 26

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

Answer 26

Dimeric

Question 27

How does insulin effect Fatty Acid Synthase?

Answer 27

Upregulates the amount of enzyme expressed

Question 28

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

Answer 28

``` Cysteine-SH group; Condensing Enzyme (CE) domain ```

Question 29

What is added in the second reaction of FA synthesis?

Answer 29

Malonyl CoA

Question 30

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

Answer 30

ACP sulfhydryl group | ACP= acyl carrier peptide

Question 31

What occurs during the 3rd reaction of FA synthesis?

Answer 31

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

Question 32

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

Answer 32

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

Question 33

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

Answer 33

Beta-hydroxybutyryl-ACP

Question 34

What occurs in the 6th reaction of Fatty Acid synthesis

Answer 34

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

Question 35

What occurs after step 6 in FA synthesis?

Answer 35

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

Question 36

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

Answer 36

Thioesterase activity hydrolyses it, forming final free form.

Question 37

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

Answer 37

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

Question 38

Where does chain elongation of fatty acids primarily occur?

Answer 38

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

Question 39

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

Answer 39

Mitochondria; | Reversal of B-oxidation.

Question 40

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

Answer 40

Fatty acyl-CoA desaturases

Question 41

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

Answer 41

5, 6 or 9

Question 42

Why are linoleate and linolenate considered essential fatty acids?

Answer 42

Because they have unsaturations beyond carbon 9

Question 43

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

Answer 43

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

Question 44

What are the substrates in phosphatic acid synthesis?

Answer 44

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

Question 45

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

Answer 45

Glycerol-3-phosphate

Question 46

What are the substrates of TAG synthesis?

Answer 46

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