Chapter 12: 12.1 Fat Metabolism

Question 1

What initiates fat breakdown/metabolism?

Answer 1

Epinephrine/glucagon

Question 2

Fat can be used for ATP through…

Answer 2

Catabolism, Mobilization, and Oxidation

Question 3

What is fat mobilization also known as?

Answer 3

β adrenergic signalling

Question 4

Describe:

Steps in Fat mobilization

Answer 4

1. Hormone binds GCPRs on adipose cells
2. Signal transduction: Gα-GTP, adenylate cyclase, cAMP production, PKA activation
3. Hormone sensitive lipase is activated by PKA
4. TAGs converted to glycerol and 3 fatty acids

Question 5

Where are how are fatty acids activated?

Answer 5

In the cytoplasm
* Activated through the addition of a CoA (traps them in the cell)

Question 6

What is fatty acid activation performed by?

Answer 6

Acyl-CoA synthetase

Question 7

In fatty acid activation:

Acyl-CoA moves into the ————- —— where ————– occurs

Answer 7

• Mitochondrial matrix
• Beta-oxidation

Question 8

In fatty acid activation:

How does Acyl-CoA move into the mitochondrial matrix?

Answer 8

• Passes through the outer membrane through porins
• Passes through the inner membrane via carnitine shuttle

Question 9

How many steps does beta oxidation occur through?

Answer 9

Occurs in 4 steps

Question 10

Describe:

The steps of beta oxidation

Answer 10

1. Acyl CoA dehydrogenase: Double bond formation in the fatty acid chain (FADH2 produced)
2. Hydratase: Adds water across the bond, introducing a hydroxyl group
3. Dehydrogenase: Converts hydroxyl group to ketone group (NADH produced)
4. Thiolase: Cleaves acetyl-CoA from the fatty acid chain and leaves the fatty acyl-CoA with two less carbons

Question 11

What can a 16-carbon CoA yield?

Answer 11

8 acetyl CoA + 7 NADH + 7 H+ + 7 FADH2

Question 12

True or False:

Beta oxidation yields more ATP than glucose

Answer 12

True

Question 13

What is the limitations of the Citric Acid Cycle?

Answer 13

Limited by oxaloacetate (derived from pyruvate)

Question 14

What does “hitting the wall” during exercise mean?

Answer 14

When no more glycogen is available
* ATP production from fat is limited by oxaloacetate

Question 15

How many stages does fatty acid synthesis occur in? State them

Answer 15

3 stages:
1. Mitochondrial acetyl-CoA gets exported to the cytoplasm
2. Acetyl-CoA carboxylase (ACC) converts acetyl-CoA to malonyl-CoA
3. Fatty Acid Synthase (FAS) converts malonyl-CoA into fatty acid chains

Question 16

In fatty acid synthesis:

In the first stage:
* How is acetyl-CoA exported to the cytoplasm?
* Why?

Answer 16

Exported to the cytoplasm through the Citrate-Malate-Pyruvate Shuttle
* Acetyl-CoA cannot pass through the mitochondrial inner membrane

Question 17

In fatty acid synthesis:

In stage 2:
* It is a ——— and ——— step
* Uses —

Answer 17

• Regulated, committed
• ATP

Question 18

In fatty acid synthesis:

In stage 2, what are the 2 reactions that occur to convert acetyl-CoA to malonyl-CoA?

Answer 18

1. Carboxylation of biotin with ATP
2. Transfer of carboxyl group to acetyl-CoA

Question 19

In fatty acid synthesis:

In stage 2, describe the regulation of ACC

Answer 19

• Activated by citrate
• Inhibited by phosphorylation and palmitoyl-CoA

Question 20

In fatty acid synthesis:

In stage 2, what does malonyl-CoA inhibit?

Answer 20

Inhibits carnitine acyltransferase 1 during beta oxidation

Question 21

In fatty acid synthesis:

In stage 3, describe FAS

Answer 21

A large dimer with 10 active sites

Question 22

In fatty acid synthesis:

In stage 3, describe ACP

Answer 22

Acyl Carrier Protein
* Contains a phosphopantetheine group

Question 23

In fatty acid synthesis:

In stage 3, list the reactions that malonyl-CoA undergoes to be converted into fatty acid chains

(5 points)

Answer 23

• Acetyl-CoA and malonyl-CoA bind to the ACP which condeses them to β-keto-acyl-ACP and CO2 is released
• Two redox reaction occur through β-ketoacyl reductase (KR) and β-enoyl reductase (ER)
• H2O is released by dehydratase (DH)
• Chain accepts 2 more carbons from malonyl-CoA
• Thioesterase (TE) adds an H2O to the fatty acid and releases it from the ACP

Question 24

To generate a 16 carbon chain, what is required?

Answer 24

• 7 cycles of FAS
• 1 acetyl-CoA and 7 malonyl-CoA
• ACC requires 7 ATP and FAS uses 14 NADPH

Question 25

In fatty acid synthesis:

Where does elongation of the 16 carbon chain occur?

Answer 25

ER

Question 26

In fatty acid synthesis:

What happens in denaturation?

Answer 26

Desaturases introduce double bonds within the first 9 carbons
* Anything past the 9th carbons comes from diet (omega 6 and omega 3)

Question 27

What do desaturases require to work?

Answer 27

NADPH and O2

Question 28

In fatty acid synthesis:

Where does triacylglyceride formation occur?

Answer 28

In liver and adipose tissue

Question 29

In fatty acid synthesis:

Describe triacylglyceride formation

Answer 29

• Phosphatidate is converted to diacylglycerol by phosphatase
• Diacylglycerol acyltransferase converts diacylglycerol to triacylglycerol