STPM Biology - chapter 4(old syllabus) chapter 6 (new syllabus): Revision essay question 9

9. Describe the mechanism of action in synthesis of lipid by photosynthesis.

Answer

1. Lipid Synthesis
1. Fatty acid synthesis is catalyzed by fatty acid synthetase using the substrates acetyl-CoA and malonyl-CoA, the reductant NADPH, and a small protein called acyl carrier protein, which carries the growing fatty acid chain; the fatty acid is lengthened by adding two carbons at a time to its carboxyl end
2. Triacylglycerols are formed from the reduction of dihydroxyacetone phosphate (a glycolytic pathway intermediate) to glycerol 3-phosphate, which then undergoes esterification with two fatty acids to form phosphatidic acid; this can then be used to produce triacylglycerol
3. Phospholipids are also produced from phosphatidic acid using a cytidine diphosphate (CDP) carrier

•Lipid Anabolism - lipid synthesis is known as lipogenesis

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Øglycerol is synthesized from dihydroxyacetone phosphate (an intermediate product of glycolysis)

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Ømost lipids, including nonessential fatty acid chains and steroids, begin with acetyl-CoA

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Ølipogenesis can use almost any organic substrate because lipids, amino acids, and carbohydrates can be converted to acetyl-CoA

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Ønot every fatty acid chain that can be broken down can be built; thus, fatty acids that cannot be built must be obtained in the diet and are called essential fatty acids (e.g. linoleic acid and linolenic acid are essential fatty acids)

animation

http://ull.chemistry.uakron.edu/pathways/FA_synthesis/index.html