TAG Degradation, FA Oxidation, Ketone body Review Slides

Question 1

What hormone stimulates the conversion of triacylglycerol to fatty acids? Where does this occur?

Answer 1

Epinephrine- it stimulates the HSTL (hormone sensitive triacylglycerol lipase) to break down triacylglycerol into fatty acids

This is occurs in adipose tissue. Fats are stored as TAG’s in adipose tissue, and are mobilized for energy by epinephrine.

Question 2

How is biosynthesis of fatty acids affected by epinephrine?

Answer 2

Fatty acid biosynthesis is inhibited by epinephrine.

Question 3

How is ketone body formation affected by epinephrine?

Answer 3

Ketone body formation is stimulated by epinephrine

Question 4

How is gluconeogenesis affected by epinephrine?

Answer 4

Gluconeogenesis formation is stimulated by epinephrine

Question 5

How is glycolysis affected by epinephrine?

Answer 5

Glycolysis is inhibited by epinephrine

Question 6

Where does the oxidation of fatty acids occur?

Answer 6

Fatty acid oxidation (beta-oxidation) occurs in the mitochondrial matrix.

Question 7

Free fatty acids cannot diffuse into the mitochondrial matrix for beta oxidation. How do they get there?

Answer 7

Fatty acids are converted to fatty acyl-CoA by Acyl-CoA synthase.

Carnitine then transports the fatty acid into the mitochondrial matrix using the carnitine palmitoyl transferase-1.

Question 8

What form are fatty acids transported into mitochondrial matrix for beta oxidation?

Answer 8

Acylcarnitine

Question 9

What substance inhibits Carnitine palmitoyl transferase I? Explain.

Answer 9

Malonyl CoA

Malonyl CoA is the product of the reaction catalyzed by acetyl-CoA carboxylase, the rate limiting enzyme in fatty acid biosynthesis. Therefore, high levels of malonyl CoA are indicative of high energy status.

Question 10

How does decreased malonyl CoA affect fatty acid beta oxidation?

Answer 10

Decreased malonyl CoA increases fatty acid oxidation.

Question 11

Where does ketone body formation occur?

Answer 11

Ketone body formation occurs in the liver

Question 12

Where does ketone body utilization occur?

Answer 12

Everywhere except for the liver

Question 13

Which is the rate-limiting enzyme in ketone body formation?

Answer 13

HMG-CoA synthase

Question 14

What is the rate limiting step in ketone body catabolism?

Answer 14

acetoacetate: succinyl CoA transferase (thiophorase)

Question 15

What hormonal regulation stimulates the release of TAG’s (in adipose tissue) into free fatty acids?

Answer 15

An increase in epinephrine and a decrease in insulin stimulates HSTLipase to cleave TAGs into their respective free fatty acids.

Question 16

How do the free fatty acids from adipose tissue travel to the liver?

Answer 16

FFA’s “surf” through the blood on albumin

Question 17

Once in the liver, what happens to FFAs released from adipose tissue?

Answer 17

Once in the liver, FFAs are converted into Acyl-CoA. Acyl-CoA is then transferred into the into the inner mitochondrial matrix (on carnitine). Acyl CoA is then subsequently broken down into acetyl CoA’s.

Question 18

How does ketone body production start?

Answer 18

As fatty acid oxidation continues, ATP builds up in the cell and eventually inhibits the ETC. When the ETC slows down, NADH builds up and eventually stop the KREBS cycle. When the Krebs cycle stops, acetyl CoA builds up (because there is no allosteric regulation negatively inhibiting fatty acid oxidation). Acetyl CoA can then be shunted into the ketone body biosynthesis pathway

Question 19

How does malonyl CoA affect the beta oxidation of fatty acids?

Answer 19

Malonyl CoA inhibits fatty acid oxidation. This makes sense, as malonyl CoA is an intermediate in fatty acid biosynthesis. It doesn’t make sense to break down fatty acids and build them up at the same time.

Question 20

Carbohydrates are broken down into acetyl CoA in the liver. What happens when citrate and insulin levels are high?

Answer 20

Acetyl CoA carboxylase (requires biotin) is inhibited.

Question 21

How does the activation of Acetyl-CoA carboxylase affect ketone body formation?

Answer 21

Decreases. If acetyl CoA carboxylase is stimulated, fatty acids are being synthesized. Ketone production is linked to fatty acid oxidation, which is counterproductive to the fatty acid biosynthesis