Coenzymes are small organic molecules that are required by enzymes to carry out their catalytic functions. They act as cofactors, assisting enzymes in various metabolic reactions. Coenzyme-II refers specifically to the coenzyme NADP (nicotinamide adenine dinucleotide phosphate).

Explanation:
NADP (Nicotinamide Adenine Dinucleotide Phosphate) is a coenzyme that functions as an electron carrier in many biological reactions. It is derived from the molecule NAD+ (Nicotinamide Adenine Dinucleotide) by the addition of a phosphate group.

NADP and NAD+ play crucial roles in redox reactions, which involve the transfer of electrons from one molecule to another. In these reactions, NADP/NAD+ can accept electrons (becoming reduced) or donate electrons (becoming oxidized), thus serving as an electron carrier.

Key points:
- Coenzyme-II is NADP (Nicotinamide Adenine Dinucleotide Phosphate).
- NADP is derived from NAD+ by the addition of a phosphate group.
- NADP/NAD+ function as electron carriers in redox reactions.
- They can accept or donate electrons, depending on the specific reaction.

Examples of NADP/NAD+ functions:
1. Photosynthesis: NADP+ is reduced to NADPH during the light-dependent reactions of photosynthesis. NADPH carries the electrons needed for the synthesis of glucose from carbon dioxide.
2. Cellular respiration: NAD+ is reduced to NADH during the breakdown of glucose in glycolysis, the Krebs cycle, and oxidative phosphorylation. NADH transfers electrons to the electron transport chain, leading to the production of ATP.
3. Fatty acid synthesis: NADPH provides the reducing power required for the synthesis of fatty acids.

In summary, coenzyme-II refers to NADP, which is involved in various metabolic reactions as an electron carrier. It plays a crucial role in processes such as photosynthesis, cellular respiration, and fatty acid synthesis.