Lecture37: Fatty Acid Catabolism

Question 1

What are some sources of fat?

Answer 1

• diet
• stored in cells (adipocytes)
• synthesized in one organ and exported to another

Question 2

What is the average for the daily energy requirement o humans that is obtained by dietary triacylglycerols?

Answer 2

40%

Question 3

Where does fatty acid oxidation occur?

Answer 3

in the mitochondrian

Question 4

Where does beta-oxidation take place?

Answer 4

Eukaryotes- mitochondria and peroxisomes

Bacteria-cytosol

Question 5

What can the Fatty acyl-CoAs formed on the cytosolic side:

Answer 5

used to synthesize membrane lipids
OR
transported into the mitochondrion

Question 6

Fatty Acid Transport

Answer 6

Fatty acids with chain lengths of 12 or less can enter without transporters
-greater than 14 and the fatty acid must be transported by carnitine shuttle

Question 7

Carnitine acyltransferase I

Answer 7

inhibited by malonyl-CoA- the first intermediate in fatty acid synthesis

Question 8

Oxidation of Fatty Acids

Answer 8

Takes place in three stages

Question 9

Stage 1 of oxidation of fatty acids

Answer 9

Beta oxidation

• fatty acids undergo oxidative removal of two carbon units in the form of acetyl-CoA starting from the carboxyl end of the fatty acyl chain
• each acetyl-CoA formed requires the removal of two pairs of e- and 4H+ by dehydrogenases

Question 10

Stage 2 of oxidation of fatty acids

Answer 10

Acetyl-CoA enters the TCA cycle to form CO2, NADH, and FADH2

Question 11

Stage 3 of oxidation of Fatty acids

Answer 11

the reduced coenzymes (NADH AND FADH2) from stages 1 and 2 are converted to their oxidized form by electron donation to O2 via the ETC (electron transport chain)
-ETC provides the proton gradient and create the proton-motive forced used to make ATP via F0F1ATPase

Question 12

Reactions of Beta Oxidation

Answer 12

1) oxidation
2) Hydration
3) Further oxidation
4) Thiolysis

Question 13

Fatty Acid Beta-oxidation multienzyme complex

Answer 13

ECH 2-enoyl-CoA hydratase
HACD L-3-hyroxyacyl-CoA dehydrogenase
-KACT 3-ketoacyl-CoA thiolase

-results in enhanced catalytic efficiency since the active site of each enzyme is positioned in close proximity to the others due to the dimer arrangement. Thus, the ECH and HACD are positioned in a channel and diffuse to the next active site

EXAMPLE EXAMPLE OF METABOLIC CHANNELING

Question 14

Oxidation of unsaturated fatty acids

Answer 14

• The cis double bonds in fatty acyl chains cannot be acted upon by 2-enoyl-CoA hydrates
• two other enzyme- an isomerase and a reductase-are required

Question 15

Oxidation of Odd-numbered fatty acids

Answer 15

• processed the same way as the even number fatty acids except they will eventually lead to a 5 carbon acyl chain that will produce acetyl-CoA and Propionyl-CoA
• Acetyl-CoA enters the TCA cycle and propionyl-CoA is metabolized by a three enzyme pathway

Question 16

Ketone Bodies

Answer 16

are formed from acetyl-CoA in the liver of humans and most mammals during oxidation if they don’t enter the TCA cycle
-over produced in diabetic and during starvation (Ketoacidosis)

Acetone
Acetoacetate
D-B-hydroxybutyrate

Question 17

Acetoacetate/Acetone/B-hydroxybutyrate

Answer 17

• acetone is produced in low quantities compared to the others
• Acetoacetate and B-hydroxybutyrate are transported to extra hepatic tissues and converted to acetyl-CoA. This provides a fuel source for the heart and skeletal muscle and the brain can be utilized under starvation

Question 18

How many ATP are produced from Fatty acid degradation?

Answer 18

108