36 - Protein Metabolism and Metabolic Integration

36 - Protein Metabolism and Metabolic Integration -...

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HNFE 3025 Fall 2009 Integration and Regulation of Metabolism Fed, Fasting, and Starvation
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Starvation Protein synthesis decreases Reduction in mRNA needed for translation of proteins Decreased rate of peptide bond formation Even proteins with a rapid turnover (e.g., plasma proteins) are synthesized at a rate 30-40% below normal The rate of muscle protein synthesis decreases Protein degradation slows Reflected by decreased urinary 2
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Starvation Hormone balance adjusts Insulin production decreases rapidly Muscle and adipose tissue become somewhat resistant to insulin Ineffective at promoting cellular nutrient uptake for protein synthesis and lipogenesis Changes in production of counter regulatory hormones Glucagon - increases Cortisol – increases initially and then decreases Thyroid hormone, triiodothyronine (T3) decreases 3
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Starvation Glucagon Promotes fatty acid mobilization from adipose tissue Promotes ketone production Promotes availability of amino availability for gluconeogenesis Cortisol Promotes catabolism of muscle protein to provide amino acids as a substrate for gluconeogenesis T3 Reduced production results in decreased metabolic rate 4
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Starvation First few days Liver glycogen is depleted Muscle undergoes proteolysis Urinary 3-methylhistidine is a marker of myofibrillar degradation Releases a mixture of AAs with high concentrations of alanine and glutamine Alanine – preferred substrate for gluconeogenesis » Stimulates secretion of glucagon to promote gluconeogenesis » Converted to pyruvate to be used in gluconeogenesis Glutamine – taken up and used primarily by gastrointestinal tract and kidney Glucose is also made in liver from lactate and glycerol 5
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Starvation As starvation continues Tissues continually use FAs and glucose as energy sources Begin to use ketones formed in liver from FA catabolism Decreased protein catabolism and gluconeogenesis Brain and other tissues begin to rely on ketones for energy Carbon skeleton of glutamine can be used in kidney for gluconeogenesis 6
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Fatty acids used for ketone synthesis Use of ketones means less protein is needed for gluconeogenesis – slows proteolysis What proteolysis that occurs in muscle can supply AAs for synthesis of crucial plasma proteins? 7
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This note was uploaded on 03/23/2010 for the course HNFE 3025 taught by Professor Mwhulver during the Spring '10 term at Virginia Tech.

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36 - Protein Metabolism and Metabolic Integration -...

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