One of your classmates set up an in vitro respiration system using cell extracts
ID: 162125 • Letter: O
Question
One of your classmates set up an in vitro respiration system using cell extracts in which the rate of carbohydrate metabolism could be measured by monitoring the conversion of radioactive glucose to CO_2. The student found that the addition of citrate to this system led to a rapid decrease in the level of glucose; however, the addition of acetyl-CoA had little effect on the rate of glucose metabolism. Explain this observation. Citrate moves in and out of mitochondria via a specific transport protein. How would an inhibitor of this transport system affect the coordinate regulation of glycolysis and oxidative metabolism? Predict the effect of accumulation of ADP on the activity/flux of the following enzymes/pathways? Explain your reasoning (citing specific enzymes if necessary).Explanation / Answer
Answer:
1. The addition of citrate increased the capacity of the citrate cycle to metabolize acetyl CoA by increasing the concentration of all cycle intermediates, most importantly, the concentration of oxaloacetate.
The addition of acetyl CoA to this system had little effect because oxaloacetate levels were limiting and glucose metabolism was already at a maximum rate. The cycle was working at full capacity and having more substrate available for the citrate synthase reaction had little effect on the rate of glucose metabolism.
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