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

2024
Views:

33

Pages:

6
Author:

Sheha A.

Transport of Mitochondrial Acetyl CoA into Cytosol Acetyl CoA is a key metabolite formed during carbohydrate metabolism. It is produced in the mitochondria. In cytosol, it is used for the synthesis of fatty acids. Acetyl CoA cannot directly cross the mitochondrial membrane. Thus, a shuttle mechanism is required for its transport. Two major shuttle mechanisms exist: 1. Citrate shuttle 2. Malate-aspartate shuttle Citrate Shuttle: Acetyl CoA condenses with oxaloacetate to form citrate. Citrate is transported out of the mitochondria. In the cytosol, citrate is cleaved back to acetyl CoA and oxaloacetate. Oxaloacetate is transported back to the mitochondria. Malate-Aspartate Shuttle: Oxaloacetate is reduced to malate in the mitochondria. Malate is transported to the cytosol. In the cytosol, malate is oxidized to oxaloacetate, generating NADH. Oxaloacetate is then converted to aspartate and transported back to the mitochondria. Fatty acid synthase: Fatty acid synthase is a multi-functional polypeptide chain. It is a dimer of two identical subunits. Each monomer contains the activities of 7 enzymes. Fatty acid synthase is a multi-functional polypeptide chain. It is a dimer of two identical subunits. Each monomer contains the activities of 7 enzymes. Activities of 7 enzymes carried out by acyl carrier protein (ACP): Malonyl CoA Acetyl CoA Malonyl CoA Acetyl CoA Acetyl CoA Malonyl CoA Acetyl CoA Condensation Reduction Dehydration Reduction Condensation Reduction Dehydration Reduction Reaction proceeds A molecule of acetyl CoA is attached to ACP. a) A molecule of acetyl CoA is attached to the -SH group of the acyl carrier protein (ACP) of the fatty acid synthase complex. b) Two carbon acetyl group is transferred to the ketoacyl ACP synthase of the fatty acid synthase complex. Fatty Acid Synthase Complex Acetyl-ACP + enzyme-SH → Acetyl-S-enzyme + ACP The vacant -SH group of ACP accepts another molecule of acetyl CoA to form acetyl-CoA. Malonyl CoA + ACP → Malonyl-ACP + CoASH The two activated molecules, acetyl-CoA and malonyl-CoA, are attached to the fatty acid synthase complex. The enzyme malonyl transacylase is called the condensing enzyme.