Reduction and Oxidation:
Simply put, when a molecule gains electrons, it is reduced, and when a molecule loses electrons, it is oxidized. We can use a quick method to remember this - OIL RIG. Oxidation I Lose, Reduction I Gain. When a molecule is reduced, it gains an electron and also energy. On the other hand, if it is oxidized, it loses electrons and energy. The molecule that donates electrons is called the reducing agent because it allows another molecule to be reduced (although itself becomes oxidized). On the contrary, the molecule that receives electrons is called the oxidizing agent because it allows another molecule to be oxidized (although itself becomes reduced).
When a reaction requires both reduction and oxidation to occur, it is called a redox reaction.
Note that electrons do not have to be completely transferred in a redox reaction. For example, when CH4 and 2O2 reacts to form water and carbon dioxide, the CH4 is oxidized because its electrons get closer to the more electronegative oxygen without completely transferring to it.
The redox reactions of NAD+ and NADH are very important in cellular respiration. When the enzyme dehydrogenase remove two hydrogen atoms from a sugar, NAD+ takes one hydrogen ion and two electrons and becomes reduced. The product is NADH. The other hydrogen ion is simply released.
When a reaction requires both reduction and oxidation to occur, it is called a redox reaction.
Note that electrons do not have to be completely transferred in a redox reaction. For example, when CH4 and 2O2 reacts to form water and carbon dioxide, the CH4 is oxidized because its electrons get closer to the more electronegative oxygen without completely transferring to it.
The redox reactions of NAD+ and NADH are very important in cellular respiration. When the enzyme dehydrogenase remove two hydrogen atoms from a sugar, NAD+ takes one hydrogen ion and two electrons and becomes reduced. The product is NADH. The other hydrogen ion is simply released.