Fatty Acid Oxidation

Question 1

What enzyme breaks the fatty acids from the glycerol backbone?

Answer 1

lipase

Question 2

Fatty Acid is activated by adding CoA-Sh, turning it into _______ so it can undergo beta-oxidation. Where does this step occur? What enzyme controls this step?

Answer 2

Acyl-CoA
This step occurs in the cytoplasm. Once Acyl-CoA is generated, it can cross the mitochondrial membranes into the mitochondrial matrix
The enzyme required for this step is acyl-CoA synthetase (which requires the use of 2 ATP)

Question 3

where does beta-oxidation occur?

Answer 3

in the mitochondrial matrix

Question 4

What is the purpose of beta-oxidation of acyl-CoA

Answer 4

through beta oxidation, the acyl-CoA undergoes a repeated series of 4 rxns which cleave the bond between the alpha and beta carbonds to liberate an Acetyl-CoA in addition to generating one FADH2 and NADH. The Acetyl-CoA is then used in the Kreb’s cycle.

Question 5

Briefly describe the first step of beta-oxidation

Answer 5

The acyl-CoA gets oxidized, and a double bond forms between the alpha and beta C (from the carbonyl carbon). While acyl-CoA gets oxidized, FAD gets reduced into FADH2

Question 6

Briefly describe the second step of beta-oxidation

Answer 6

The C=C (between the alpha and beta C) of acyl-CoA undergoes hydration oxidation (water is added to the beta carbon as OH and then oxidized to O), turning the beta carbon into a carbonyl carbon.

Question 7

Each round of beta oxidation cleaves a 2 acetyl-CoA from the molecule; however, the final round cleaves a __1__ fatty acyl-CoAto generate 2 ___2____

Answer 7

1. 4 carbon

2. acetyl-CoA

Question 8

Lauric acid is a twelve carbon saturated fatty acid. 2 ATP will turn this into an acyl-CoA, which will then undergoe ___ rounds of beta-oxidation, producing ____ molecules of Acetyl-CoA, ____ molecules of NADH, and ____ molecules of FADH2

Answer 8

5 rounds of beta oxidation

6 molecules of acetyl-CoA

5 NADH molecules

5 FADH2 molecules

Question 9

For unsaturated fatty acids undergo beta-oxidation, what additional steps must be taken (or what enzymes have to be utilized) to completely oxidize the FA?

Answer 9

A monounsaturated FA requires the use of an isomerase to remove the double bond, which allows the continuation of the FA’s oxidation.

A polyunsaturated FA requires the use of an isomerase and a reductase to remove the multiple C=C so that the FA can continue through beta-oxidation

Question 10

For an even numbered FA, what equations do you use to determine the number of acetyl-CoA produced from a FA chain and the number of beta oxidation cycles that a FA chain undergoes?

Answer 10

acetyl-CoA produced = #C on FA chain/2

beta-oxidation rounds = (#C on FA chain/2) -1

Question 11

For odd numbered FA, what equations do you use to determine the number of acetyl-CoA produced from a FA chain and the number of beta oxidation cycles that a FA chain undergoes?

Answer 11

use the same equation for both the # of acetyl-CoA and the # of beta-oxidation: (#C in FA/2) - 1
You won’t get a whole number, so you round down to the nearest whole number to get your final answer

Question 12

How many ATP can be produced from one lauric acid (a 12 C FA)?

Answer 12

78 ATP from lauric acid

Breakdown of calculations: 
# acetyl CoA = 12/2 = 6. Each acetyl CoA produces 3 NADH, 1 FADH2, and 1 GTP. This equates to 18 NADH, 6 FADH2, and 6 GTP. 
# beta-oxidation rounds = 5. This produces 5 NADH and 5 FADH2.
Total = 23 NADH, 11 FADH2, and 6 GTP
(23x2.5) + (11 x 1.5) + (6 x 1) = 57.5 + 16.5 + 6 = 80. Minus 2 ATP required from beginning of FA oxidation. 80 - 2 = 78 ATP from lauric acid

For MCAT, rounding to make math easier should get you to an answer that is close enough to the correct answer given in the answer choices.

Question 13

How would you overall calculate the number of ATP molecules produced from a certain #C FA?

Answer 13

• Determine # acetyl-CoA produced and # of beta-oxidation rounds the FA will undergo.
• From this, you can determine how many NADH, FADH2, and GTP will be produced from all of the acetyl-CoA (3 NADH, 1 FADH2, and 1 GTP from each acetyl-CoA); and how many NADH and FADH2 will be produced from beta-oxidation (1 NADH and 1 FADH2 per one round of beta-oxidation)
• Then calculate amount of ATP: 2.5 ATP per NADH, 1.5 ATP per FADH2, and 1 ATP per GTP)

Question 14

What is ketogenesis?

Answer 14

The development of ketone bodies by the liver for the purpose of providing an energy source for the brain. Acetyl-CoA cannot cross the blood brain barrier, so it is converted in the liver to ketone bodies (acetone, acetoacetate and beta-hydroxybutyrate) which can then cross the blood brain barrier. Once the ketone bodies reach their target organ, they are converted back into acetyl-CoA and enter into the Krebs cycle.

Question 15

what are the 3 ketone bodies generated during ketogenesis?

Answer 15

acetone, acetoacetate, and beta-hydroxybutyrate

Question 16

Briefly describe the third step of beta-oxidation

Answer 16

CoA-Sh attacks the second carbonyl, kicking off the alpha carbon between the 2 carbonyls, ultimately forming an acetyl-CoA and an acyl-CoA (that is now 2 carbons shorter than the starting acyl-CoA)

Question 17

Ketogenesis can take place when adequate glucose is present in the blood but cannot enter the cell. For instance, this occurs in type 1 diabetic patients, which lack insulin. Why would this produce ketogenesis, and why does this lead to acidosis?

Answer 17

Without insulin, glucose cannot enter the cell to undergo glycolysis, which means that the cells have no glucose to utilize as energy. So, with little to no glucose available to produce ATP, the cells start breaking down FA for energy.
High levels of acetyl-CoA that are produced from FA oxidation start to get converted into ketone bodies, which are acidic. Enough ketone bodies can make the blood acidotic, leading to ketogenic acidosis.