This document discusses lipid metabolism and fatty acid oxidation. It explains that lipids are molecules that contain hydrocarbons and make up the structure and function of living cells. Fatty acids are an important source of energy and undergo oxidation to be degraded. There are three main types of fatty acid oxidation: beta-oxidation, alpha-oxidation, and omega-oxidation. Beta-oxidation occurs in the mitochondria and involves activating fatty acids to acetyl-CoA, transporting them into the mitochondria, and undergoing four reactions - oxidation, hydration, oxidation again, and cleavage - to sequentially remove two-carbon fragments as acetyl-CoA at each turn of the cycle.
2. Lipids :
• Lipids are molecules that contain hydrocarbons and make up
the building blocks of the structure and function of living cells.
• Details of lipids already discussed in unit -1 biomolecules
• Refer unit 1 notes .
3. Fatty acid oxidation:
• The fatty acid in the body are mostly oxidized by beta-
oxidation.
• Beta- oxidation may be defined as the oxidation of fatty acid
on the beta- carbon atom .
• This result in the sequential removal of two carbon fragment
,acetyl CoA .
4. Oxidation of Fatty Acids
Fatty acids are an important source of energy
Oxidation is the process where energy is produced by degradation of
fatty acids.
There are several types of fatty acids oxidation.
(1) β- oxidation of fatty acid
(2) α- oxidation of fatty acids
(3) ω- oxidation of fatty acids
5. STAGES OF BETA –OXIDATION
The beta oxidation of fatty acids involve three stages:
Activation of fatty acids in the cytosol
Transport of activated fatty acids into mitochondria.
Beta oxidation proper in the mitochondrial matrix
6. 1.Activation of fatty acids in the cytosol
• Fatty acids are activated to acetyl –CoA by acetyl CoA by synthetases.
• It requires two steps and requires ATP coenzymes (A and Mg++)
First step : Fatty acids reacts with ATP to form acyladenylate .
Second step : Acyladenylate combines with coenzyme A to produce
acyl CoA .
7. 2.TRANSPORT OF acyl CoA into mitochondria.
• The inner mitochondrial membrane is impermeable to fatty acids.
• A specialized carnitine carrier system operates to transport activated
fatty acids from cytosol to mitochondria.
• It requires four steps:
• FIRST STEP : Acyl group of acyl CoA is transferred to carnitine
(catalyzed by carnitine acyltransferase) present on the outer surface
of inner mitochondrial membrane resulting in the formation of acyl-
carnitine.
8. STEP -2: The acyl carnitine is transported across the membrane to
mitochondrial matrix by a specific carrier protein.
Step -3: Carnitine acyl transferase –II found on the inner surface of
inner mitochondrial membrane ) that converts acyl carnitine to acyl
CoA.
STEP -4 : Releasing of carnitine returns to cytosol .
9. Step-III ,BETA OXIDATION PROPER:
• Each cycle of beta oxidation liberating a two carbon unit –acetyl CoA
occurs in a sequence of four reactions .
1. OXIDATION
2. HYDRATION
3. OXIDATION
4. CLEAVAGE
10. 1.OXIDATION : Acyl Co A undergoes dehydrogenation by an enzyme
(FAD dependent flavoenzyme ,acyl CoA dehydrogenase).A double bond
is formed between alpha and beta carbon .
2. HYDRATION: Enoyl CoA HYDRATASE Bring about the hydration of
double bond to form beta –hydroxyl CoA.
3.OXIDATION : Beta –hydroxyl CoA hydrogenase catalyze the second
oxidation and generates NADH resulting in the formation of Beta-
ketoacyl CoA
4.CLEAVAGE: The final reaction in the beta oxidation is the liberation of
2 carbon fragment ,acetyl CoA from acyl CoA . This occurs by thiolytic
cleavage catalysed by Beta keto acyl Co A thiolase .
The new acyl Co A containing two carbons less ,than the original ,re
enters the beta oxidation cycle . This process continues till the fatty
acid is completely oxidised .
