A random mutation is introduced into one of the fenes that code for the enymes o

Question

A random mutation is introduced into one of the fenes that code for the enymes of the pyruvate dehydrogenase (PDH) complex. The PDH complex in cells that carry this mutation does not function. Upon characterizing the component subunits of this nonfunctional PDH complex, it is determined that: 1. a hydroxyl-ethyl TPP intermediate can be formed, 2. the lipoyl-lysine arm is found in its reduced state with an acetyl group attached, 3. NAD + bound to the complex remains in its oxidized state. Based on this info, which enzyme in the complex has been inactivated by the mutation? Explain your reasoning.

Explanation / Answer

Answer:

1) Suggests that E1 (pyruvate dehydrogenase) is working fine since it can form the hydroxy-ethyl TPP intermediate.

2) This suggests that the entire E1 process is carried out successfully since it transfers the acetyl group to lipoamide.

3) This suggests that E3 (dihydroxyllipoyl dehydrogenase) is malfunctioning. Why? Because normally, the transferred electrons the other two enzymes of the complex are normally utilized to reduce NAD+ to NADH. This occurs in the E3 region. That isn't happening here and NAD+ is remaining in this oxidized form.

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