β-oxidation

what can beta oxidation be defined as?

the oxidation of fatty acids on the β-carbon atom

what is beta oxidation?

a catabolic process that breaks down fatty acids in the mitochondria and peroxisomes to produce acetyl-CoA and energy (ATP)

what are the stages of beta oxidation?

1. Activation of fatty acids - in the cytosol

2. Transport of fatty acids into mitochondria

3. Beta-Oxidation proper in the mitochondrial matrix

what tissues cannot utilize fatty acids for energy?

1. brain

2. RBC

3. adrenal medulla

what occurs during fatty acid activation?

fatty acid binds to CoA with the aid of ATP to form fatty acetyl-CoA, a reaction catalyzed by thiokinase or acyl-CoA synthetase. ATP is consumed, producing AMP and PPi, equivalent to 2 ATP. occurs in the outer mitochondrial membrane and the ER. consumes 2 ATP

what occurs during the transport of Acyl CoA in to mitochondria?

the first step of beta oxidation. the inner mitochondrial membrane is impermeable to fatty acids. A specialized carnitine carrier system (carnitine shuttle) operates to transport activated fatty acids from cytosol to the mitochondria. \ Carnitine is β-hydroxy γ-trimethyl aminobutyrate, synthesized by lysine & methionine in liver & kidney

what are the first four steps of beta oxidation?

1. Activation & transfer: The fatty acyl group from acyl-CoA is transferred to carnitine by CAT-I (on the outer inner mitochondrial membrane).

2. transport: The fatty acyl-carnitine complex is shuttled into the mitochondrial matrix by translocase.

3. Re-conversion: Inside, CAT-II converts fatty acyl-carnitine back to fatty acyl-CoA.

4. Carnitine recycling: Free carnitine is transported back to the cytosol by translocase for reuse.

This shuttle ensures fatty acids can enter mitochondria for β-oxidation.

each cycle of β –oxidation, liberating a two carbon unit acetyl CoA, occurs in what reactions?

1. dehydration

2. hydration

3. dehydrogenation

4. cleavage

what occurs during the first dehydrogenation stage?

Acyl CoA undergoes dehydrogenation by an FAD-dependent flavoenzyme, acyl CoA dehydrogenase. A double bond is formed between α & β carbons (i.e., 2 & 3 carbons), and FADH2 is produced

what occurs during the hydration stage?

Enoyl CoA hydratase brings about the hydration of the double bond to form β -hydroxyacyl CoA

what occurs during the second dehydrogenation stage?

β-Hydroxyacyl CoA dehydrogenase catalyzes the second oxidation & generates NADH. The product formed is β-ketoacyl CoA.

what occurs during the cleavage step?

the final reaction in β -oxidation is the liberation of a 2 carbon fragment, acetyl CoA from acyl CoA. it occurs by a thiolytic cleavage catalyzed by β- ketoacyl or CoA thiolase (or thiolase). The new acyl CoA, containing two carbons less than the original, reenters the β- oxidation cycle. The process continues till the fatty acid is completely oxidized.

how much energy is produced in one beta oxidation cycle?

1. one FADH2 × 2 = 2 ATP

2. one NADH x 3 = 3 ATP

3. one acetyl CoA x 12 = 12 ATP

totaling 17 ATP in total