Q2. Recall that tetramethylrhodamine (TMR) is a fluorescent, positively-charged

Question

Q2.

Recall that tetramethylrhodamine (TMR) is a fluorescent, positively-charged small molecule. It is used to measure mitochondrial electrical potential, by measuring the extent to which the TMR molecule enters mitochondria. The brightness of the signal from TMR is directly related to the negative charge in the matrix.

Given your exploration of how these compounds affect membrane potential, how would you expect them to affect the TMR signal in mitochondria?

Part 1. The addition of oligomycin (an ATP synthase inhibitor) will ----------- the TMR signal.

Select ONE option for the blank:

1. increase

2. decrease

Part 2. The addition of FCCP (a protonophore that allows leakage of protons across the membrane) will ---------------- the TMR signal.

Select ONE option for the blank:

1. increase

2. decrease

Part 3. The addition of cyanide (a complex IV inhibitor) will ---------------- the TMR signal.

Select ONE option for the blank:

1. increase

2. decrease

Explanation / Answer

1. The addition of oligomycin (an ATP synthase inhibitor) will increase the TMR signal because membrane potential will be less positive since H+ cannot enter matrix, so more negative chrage in matrix.

2. The addition of FCCP (a protonophore that allows leakage of protons across the membrane) will decrease the TMR signal because it will allow free flow of proteons and matrix will be less negative.

3. The addition of cyanide (a complex IV inhibitor) will increase the TMR signal , beacuse ETC will be inhibited, no protons wll enter the matrix so matrix is more negative.

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