Biochemistry Study Set 13

Biology

Quiz 7 :

Glycolysis

Quiz 7 :

Glycolysis

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Explain why fructose has the same ATP balance as glucose, even though the second phosphorylation is at the three-carbon stage in fructose metabolism, but at the sixcarbon stage in glucose metabolism.
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The pathways for the glucose and fructose metabolism are as follows:
img From above, it gets clear that the energy production becomes same in both the pathways. But the positive point of fructose pathway is that the fructose pathway bypasses the rate limiting step of the glucose metabolism that is carried out by phosphofructo kinase.

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Pancreatic cells secrete insulin in response to glucose. Here GLUT2 plays an important role as part of the "glucose sensor." Explain.
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The pancreatic cells secrete insulin from the beta cells of its Islets of Langerhans. The cells consist of GLUT2 (Glucose transporter 2) sensors inside its cytoplasm. When the insulin comes in contact with the plasma membrane of the cells, the GLUT2 sensors come close to the surface of the plasma membrane. These GLUT2 sensors act as channels for the transportation of glucose inside the cells.

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Studied in vitro, all of the kinase reactions are inhibited, even by physiological levels of ATP. However, the concentration of ATP in cells is virtually constant. Can ATP be considered a regulator of glycolysis?
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ATP (Adenosine triphosphate) is the energy molecule which is important for many cellular reactions. The ATP molecule is used as well as produced in the glycolysis process. The ATP is used in the first three-four steps of glycolysis in which the step catalyzed by phosphofructo kinase is a rate limiting step. The first three-four steps of glycolysis are as follows:
img The steps 1 and 3 of glycolysis require ADP to form ATP while in further reactions ATP is used up. These reactions are catalyzed by kinase enzyme. Thus, if there will be more ATP then the reaction requiring ATP and catalyzed by kinase would not occur. Hence, the ATP molecules can be considered as the regulator of glycolysis.

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What is the effect of arsenate ingestion at high altitudes, where the red cell shunt mutase is more active?
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In liver, pyruvate kinase is a substrate of protein kinase A, but so too is PFK-2. Explain how both of these will affect the rate of glycolysis.
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Identify the reaction mechanisms that use an electron sink.
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The P-glycerate kinase reaction is near-equilibrium, yet it leads to production of ATP, a high-energy intermediate. Explain this conundrum.
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Both NAD + , H, and TPP are enzyme cofactors; however, TPP does not rely on other reactions for its regeneration. Why is this so?
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The product of the enolase reaction would appear from the reaction mechanism to be an enol rather than pyruvate. How can this be explained?
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