Metabolism and High Protein Consumption
1. Identify those TCA cycle intermediates that are alpha-keto acids. a. Oxaloacetate, pyruvate, alpha-ketoglutarate, 2. Is pyruvate an alpha keto-acid? Explain. b. Pyruvate is an alpha keto-acid because it contains both a carboxylic acid and a ketone group. 3. Alanine is used to transport nitrogen to the liver from the muscle. What alpha keto acid is transaminated to make alanine in the muscle? c. Alpha ketoglutarate 4. Once the alanine arrives in the liver the nitrogen is removed and transaminated onto alpha-ketoglutarate.
What are the products of this reaction? d. Ammonia, pyruvate and glutamate. 5. What is the first step in the degradation of most amino acids? e. Transamination or deamination. 6. What step in urea synthesis is regulated? f. Argininosuccinate synthetase. This enzyme is responsible for the conversion of aspartate to citrulline and requires ATP and Mg2+. 7. What happens to the carbon fragment that remains after the nitrogen is removed from an amino acid? g.
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The alpha ketoacids that remain after deamination are then metabolized for energy, glucose, ketone bodies, cholesterol, or fatty acids. 8. Some amino acids are said to be glucogenic and some are ketogenic. What does this mean? h. Glucogenic amino acids can provide pyruvate or TCA Cycle intermediates to be used in gluconeogenesis, whereas, ketogenic amino acids can contribute to the synthesis of fatty acids or ketone bodies. 9. The enzymes that catalyze reactions in the urea cycle are induced during high protein diets and during starvation.
Explain. i. The reason that these enzymes are abundant during both times of high protein consumption and starvation is because in times of high protein consumption, there is a large quantity of amino acids—leading to excess nitrogen. This nitrogen needs to be removed from the body, so urea synthesis is heightened. During starvation, the body switches from carbohydrate utilization to lipid and protein utilization. During the protein metabolism, more proteins are being broke down and creating more nitrogen that must be excreted as urea.