What is a cofactor, a coenzyme, a prosthetic group?
A cofactor is essentially anything in a protein structure that is not covalently attached to the peptide backbone. Cofactors can be metal ions (iron, zinc) or organic molecules (NAD, FAD, CoA, heme). The latter are called coenzymes. A prosthetic group is a coenzyme that is tightly bound to the enzyme. 3. What is a holoenzyme, apoenzyme? A: Holoenzyme = apoenzyme + cofactors. The peptide chain without cofactors is the apoenzyme or apoprotein. 4. How does an enzyme act as a catalyst in chemical reactions? A: The enzyme’s active site lowers the activation energy of a chemical reaction. This makes the reaction more likely. 5. What is the “transition state” in a chemical reaction? A: You can think of it as a position half-way in between the substrate (what you start with) and the product of a reaction. It is the highest energy point along the reaction. The enzyme stabilizes the transition state (lowers its energy) and thereby favors the reaction. See figure 4.4. 6. How can an enzyme lower t
