74) Several steps in glycolysis are highly regulated. Overall reactions of glyco

Question

74) Several steps in glycolysis are highly regulated. Overall reactions of glycolysis are regulated by insulin and glucagon. What do they do?

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75) Calcium ion (Ca++) stimulates isocitrate to a-ketoglutarate and a-ketoglutarate to succinyl CoA reactions. Where does Ca++ come from?

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76) Number of amino acids can participate in energy metabolism. How do protein metabolism and carbohydrate metabolism intersect?

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77) During fasting, glycogenolysis starts first and then large amount of fatty acids are released from adipose tissue into the blood. The liver receives large part of it and use for b-oxidation. As a result of b-oxidation, how gluconeogenesis is regulated?

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78) Glycogenolysis is regulated by insulin to glucagon ratio. The enzyme that degrades glycogen is active when it is phosphorylated by another kinase that is active when phosphorylated also by PKA. How does high and low insulin-to-glucagon ratio influence degradation of glycogen?

Explanation / Answer

74.

Insulin and glucagon are the two hormones produced by pancreas. They both are chemically protein. But, the physiological actions produced by both the hormones are quite opposite. Insulin reduces the blood glucose level, whereas, glucagon raises the blood glucose level.

Insulin influences glucose metabolism in various tissues, including liver. In liver, it inhibits the glycogen breakdown (glycogenolysis) and the synthesis of new glucose molecules (gluconeogenesis), but stimulates glycogen synthesis. Whereas, the effects produced by glucagon are opposite to insulin. So, these hormones act antagonistic to one another to maintain homeostasis.

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