Question

1. An individual has an excess of glucose and converts the glucose into fatty acids for better storage capacity. Briefly review the steps required. Can the opposite occur?
2. An individual has an excess of amino acids and converts the amino acids into fatty acids for better storage capacity. Briefly review the steps required. Can the opposite occur? Why or why not?

Answer 1

Body converts excess dietary glucose into fat through the process called fatty acid synthesis and are stored as triglycerides. The location of this process is cytoplasm. The immediate substrate is acetyl CoA and end product is free palmitate.

The steps involved in this process are pointed below:

1. Transfer of Acetyl CoA from mitochondria to cytoplasm.

2. activation of acetyl CoA and synthesis of malonyl CoA

3. five step elongation cycle of fatty acid via ACP intermediates.

here fatty acid are synthesized by repetitive condensation cycles of two carbon units derived from malonyl CoA. One cycle goes through 4 steps

a) condensation

b) 1st reduction with NADPH

   c) dehydration

d) 2nd reduction with NADPH

So total seven cycles gives rise to palmitoyl group and release of fatty acid occurs.

The reverse of this process is called beta oxidation of fatty acid. It is the catabolic process where fatty acid is broken down to acetyl CoA, NADH, FADH2. Acetyl CoA enters citric acid cycle and NADH , FADH2 used as co-enzymes in electron transport chain.

In the case of amino acid, the excess amino acid cannot be stored and are catabolised in to glucose or fat. Hence ketogenic amino acid will be converted in the liver to triacylglycerol which is then packed and released as VLDL ( very low density lipoprotien). The reverse of this process does not occur normally.