Enzymes are proteins that catalyze, or affect the rate, of chemical reactions without themselves being altered in the process. Specific enzymes catalyze each cellular reaction.
The main role of enzymes during the respiration reaction is to assist in transferring electrons from one molecule to another. These transfers are called “redox” reactions, where the loss of electrons from one molecule (oxidation) must coincide with the addition of electrons to another substance (reduction).
Glycolysis
This first step of the respiration reaction takes place in the cytoplasm, or fluid, of the cell. Glycolysis consists of nine separate chemical reactions, each catalyzed by a specific enzyme.
The key players in glycolysis are the enzyme dehydrodgenase and a coenzyme (non-protein helper) called NAD+. Dehydrodgenase oxidizes glucose by stripping two electrons from it and transferring them to NAD+. In the process glucose is “split” into two molecules of pyruvate, which continue the reaction.
Glycolysis, the one metabolic pathway found in all living organisms, occurs in the cytoplasm of a cell and does not require oxygen to take place. Each of the 10 steps of glycolysis is catalyzed by an enzyme specific to that reaction. Initially two molecules of ATP, the cellular energy currency, are used to activate a molecule of glucose for glycolysis, but the entire process results in a net gain of two ATP molecules. The biochemical pathways of glycolysis also lead to the reduction of two molecules of NAD+ resulting in two molecules of NADH, which can be used to create ATP in later steps of cellular respiration.
