Respiration160-page14

Respiration160-page14 - During starvation or fasting or...

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Cell Respiration - 14 Some Notes Some of the steps in nutrient inter-conversion can work in both directions. Acids from the Krebs cycle can be used to synthesize some amino acids, and acetyl can be used to synthesize fatty acids. (About half the amino acids are non-essential in this sense; they can be made from other amino acids or from other acids in the cells.) Fats are more energy rich than carbohydrates. A gram of fat potentially can produce two times as much ATP as a gram of carbohydrate. Most moderate muscle activity, such as breathing and heartbeat, routinely uses a mixture of fats and carbohydrates. However, use of fatty acids for fuel is a strictly aerobic process. All anaerobic respiration must have glucose. Also, fatty acid fragments cannot normally cross the brain membrane barriers so that the brain does not use fats for fuel.
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Unformatted text preview: During starvation or fasting, or when there is insufficient carbohydrate for energy needs, the body uses its protein from body tissues to produce glucose fuel molecules for the brain and red blood cells. (Some amino acids can be converted to pyruvate and by reversing the steps of glycolysis to glucose.) • When fat reserves are mobilized in response to insufficient calories or insufficient carbohydrate in the diet, some of the fatty acid fragments combine to form ketone bodies rather than acetyl. These ketone bodies enter into circulation. Muscle and some other tissues can use ketone bodies for fuel, and ketone bodies can provide energy to some brain cells. However, some ketone bodies contain carboxyl groups forming keto acids that can cause ketosis, a condition that lowers the pH of the blood and impairs health....
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