University:
Liberty University
Course:
BIOM 500 | Introduction to Biomedical Sciences
Academic year:

2024
Views:

226

Pages:

6
Author:

Sheha A.

**β-oxidation of Fatty Acid** * Removal of 2 carbon (in the form of CO₂) at a time from the carbonyl end (α-carbon) of fatty acid is termed as β-oxidation of fatty acid. * This pathway does not produce any ATP and is a preparatory step. * The enzymes required for β-oxidation are α-hydroxylase and α-oxidase. **Intracellular Site:** * Microsomal endoplasmic reticulum **Importance of β-oxidation** * Phytanic acid (obtained from milk) has a methyl group at its β-carbon that prevents β-oxidation. * This methyl group is removed by α-oxidation to form pristanic acid which can undergo β-oxidation. **Refsum Disease** * It is caused due to absence of enzyme α-hydroxylase. * It leads to accumulation of phytanic acid in brain. * Symptoms include neurological disorders. ω-Oxidation of Fatty Acids This is a minor pathway involving oxidation of ω-carbon (last carbon) by the enzyme hydroxylase. The α-carboxyl group is converted (broken) to -COOH. Then β-oxidation takes place, either both the ends (dicarboxylic acid) or one end (ω-suberic acid) which is excreted in urine. This reaction takes place in liver microsomes. Peroxisomal Fatty Acid Oxidation This system facilitates the oxidation of very long chain fatty acids (C20-C26). This is a modified form of β-oxidation and is called α-oxidation. In this pathway, oxidation occurs at α-carbon and not β-carbon. This oxidation does not generate energy (no phosphorylation and ATP generation directly linked to this). Fatty acids longer than C12 do not attack β-oxidation. α-oxidation and β-oxidation occur to convert it to mitochondrial β-oxidation form. This system shortens the side chain of cholesterol in bile acid formation. It also takes place in the synthesis of ether glycerophospholipids and cholesterol. **Lipogenesis** When excess of glucose are consumed in the diet, it is generally converted to fatty acids and then stored in the form of triglycerides. **De Novo Synthesis of Fatty Acid** * It is also called as Extra-mitochondrial or cytoplasmic synthesis of fatty acid. * This pathway is mainly occurs in cytosol. * Palmitic acid is the major fatty acid synthesized. **Tissue Site:** * Primarily in liver & mammary glands * Smaller extent - in the adipose tissue / brain & kidney **Intracellular Site:** * Cytosol **Starting material:** Malonyl CoA **End product:** Palmitic acid