Question

In cellular respiration, what is being oxidized and what is being reduced?

Answer 1

`"NAD"^+` and `"FADH"` are being reduced and later oxidezed. The molecule they receive the electrons from are being oxidized.

Explanation:

`color(red)"The basic terms"`
Oxidation and reduction is about the transfer of electrons:

• oxidation = a molecule loses electrons
• reduction = a molecule gains electrons

`color(red)"Electron carriers in cellular respiration"`
An important part of cellular respiration is the transfer of electrons. In the first two phases of cellular respiration (glycolysis and Krebs cycle) electrons are transferred to a carrier molecule. In the third phase (electron transport chain) the electrons are taken from the carrier and used to make energy (ATP).

The carriers are:

• Nicotinamide adenine dinucleotide
  `"NAD"^+ + "2H" + 2 e^- " " harr " " "NADH" + "H"^+`
• Flavin adenine dinucleotide
  `"FAD" " "+ "2H" + 2 e^- " " harr " " "FADH"_2`

`color(Red)"What gets reduced and what gets oxidized?"`
The molecules `"NAD"^+` and `"FADH"` gain electrons, so these are being reduced .

Electrons are coming from molecules in glycolysis and the Krebs cycle, these are being oxidized :

• glyceraldehyde-3-phosphate
• pyruvate
• isocitrate
• `alpha`-ketoglutatrate
• succinate
• malate

In the last phase of cellular respiration, the electron transport chain, `"FADH"_2` and `"NADH"` are also being oxidized when they give off their gained electrons.