Ubiquinone has an absorbance band at 275 nm. This band bleaches when the quinone

Question

Ubiquinone has an absorbance band at 275 nm. This band bleaches when the quinone is reduced to either the semiquinone or the dihydroquinone. The semiquinone has an absorbance band at 450 nm, but neither the quinone nor the dihydroquinone absorbs at this wavelength. A suspension of purified bacterial reaction centers was supplemented with extra ubiquinone and reduced cyctochrome c and was then illuminated with a series of short flashes of light. The absorbance at 275 nm decreased on the odd-numbered flashes as shown on the first curve. The absorbance at 450 nm increased on the odd numbered flashes but returned to the original level on the even-numbered flashes as shown in the second curve.

a. Why does the absorbance at 275 nm decrease on odd-numbered flashes but not on even-numbered flashes?

b. Why does the absorbance at 450 nm increase on the first flash but decrease on the second flash?

c. Why is it necessary to have reduced cytochrome c present in order to see these effects?

Make sure to explain how you arrived at your answer.

Explanation / Answer

a) Absorbance at 275nm decrease on odd numbered flashes but not on even numbered flashes because molecule of ubiquinone, R, is reduced to the semiquinone (R-) after odd-numbered flashes and reoxidized after even-numbered flashes.

b) Absorbance at 450nm increase on the first flash but decrease on the second flash is due to the extent of electrogenic reaction caused during the process after formation of first flash is more than the second flash.

c) Reduced Cytochrome C is necessary in order to these effects because it is essential in shuttling the electrons during the reaction.

Related Questions

Navigate

• Browse (All)
• Browse U
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.