\" The hormonal view of appetite and weight has grown since leptin was first ide
ID: 20487 • Letter: #
Question
" The hormonal view of appetite and weight has grown since leptin was first identified in the mid 90s, and the focus has been regulation of appetite and metabolic rate. Clearly there is far more to the whole picture. Acetyl--CoA carboxylase catalyzes synthesis of malonyl Co--A which ?"a. converts succinate to malonate in the cytosol. "
"b. is the substrate for fatty acid synthesis and controls fatty acid flow to the mitochondria where ATP is synthesized. "
"c. is the substrate for glucose synthesis and controls glycogen flow to the endoplasmic reticulum where ATP is synthesized. "
"d. binds the insulin receptor stimulating fat cell division and cannabinoid release from the arcuate nucleus. "
"e. binds the peroxisome proliferator--activated receptor alpha stimulating the synthesis of ghrelin in AgRP hypothalamic neurons. "
Explanation / Answer
It's B. Malonyl CoA has a role in chain elongation in fatty acid biosynthesis. It provides 2-carbon units to fatty acids and commits them to fatty acid chain synthesis. It's used as a substrate by the enzyme malonyl coenzyme A acyl carrier protein transacylase. It also transports alpha-ketoglutarate across the mitochondrial membrane into the mitochondrial matrix. Malonyl CoA inhibits fatty acids from associating with carnitine by regulating the enzyme carnitine acyltransferase. This prevents fatty acids from entering the mitochondria where fatty acid oxidation and degradation occur. This step is rate limiting in the beta-oxidation of fatty acids.
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