Question

When NAD+ picks up two electrons and a proton in reactions of the Krebs cycle to form NADH, the NAD+:

a) Is reduced
b) Is oxidized
c) Stays the same
d) Becomes inactive

Answer 1

When NAD+ accepts two electrons and a proton to form NADH in the Krebs cycle, it undergoes reduction by gaining electrons and a proton, leading to its reduced state as NADH.

Thus option a is correct.

Step-by-step explanation:

When NAD+ accepts two electrons and a proton to become NADH in the Krebs cycle, it undergoes reduction. Reduction refers to the gaining of electrons by a molecule. In this case, NAD+ gains electrons and a proton to form NADH, indicating a reduction in its chemical state. This reduction of NAD+ to NADH allows it to carry the high-energy electrons to the electron transport chain for ATP production.

In the Krebs cycle, NAD+ functions as an electron carrier, shuttling electrons to the electron transport chain. When it accepts two electrons and a proton, it undergoes a redox reaction, where it gains electrons and is thus reduced to NADH. This reduction is vital for energy production as NADH carries the high-energy electrons harvested from the Krebs cycle to the electron transport chain, where ATP is synthesized through oxidative phosphorylation. The process maintains a continuous cycle of electron transfer and ATP generation essential for cellular energy production. Mathematically, the reduction of NAD+ can be represented as:

NAD+ + 2H+ + 2e- -> NADH + H+

This equation demonstrates the reduction of NAD+ to NADH by gaining two electrons and a proton. The resulting NADH carries the high-energy electrons to fuel ATP production, highlighting the significance of this reduction in the Krebs cycle.

Therefore option a is correct.