6) Compound A is said to be reducing Compound B. Compound A is: A) giving an ele

Question

6) Compound A is said to be reducing Compound B. Compound A is:

A) giving an electron to compound B.

B) taking an electron from compound B.




7) For chemical thermodynamic reasons that have nothing to do with biological issues, only certain energy source-TEA reactions can be used to obtain energy. Which of the following energy source-TEA combinations is NOT used by any prokaryote to obtain energy?

A) Molecular hydrogen-carbon dioxide

B) Hydrogen sulfide-molecular oxygen

C) Ammonium-nitrate

D) Nitrite-molecular oxygen





8) Despite their different names, conceptually oxidative phosphorylation and substrate level phosphorylation are similar. Which of the following are similarities between the two processes?

A) An energy source is oxidized.

B) An electron acceptor is reduced.

C) ADP is phosphorylated.

D) TWO of the above.

E) ALL of the above.

Explanation / Answer

6) This is a redox reaction. A compound is said to be reduced when it gains an electron from another compound.
A compound is said to be oxidized when it looses electrons.
Compound A is reducing compound B, thus it is giving an electron to compound B.
So A) is correct.

7) Energy source-TEA reactions are basically redox reactions taking place in a cell. These reactions produce energy for the cell to utilize. Thus terminal electron acceptors (TEA) with high reduction potentials are favored so that the energy produced is maximized. The order of preference for TEAs are:
O2 > NO3- >   Mn(VI) > Fe(III) > AsO43- >SO42-

Carbon dioxide is never used as a TEA, as is clear from the above order. O2 is most favorable under aerobic conditions. When O2 is not present (anaerobic conditions), the other compounds are used as TEAs, depending on their availability and the above-mentioned order.
So option A) is correct.
All other mentioned reactions are possible.

8) Correct option is E).
In both the processes, ADP is phosphorylated to give ATP. These are again, redox reactions. So an energy source has to be oxidized and likewise, an electron acceptor will be reduced.

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