Would glucose be considered a reactant in glycolysis? Also, some sites are saying that 4 ADP molecules are also reactants, but I don't understand how?
Yes, glucose is indeed considered a reactant in glycolysis. Glycolysis is the first step in cellular respiration, the process by which cells convert glucose or other sugars into energy in the form of ATP (adenosine triphosphate). During glycolysis, glucose is broken down into two molecules of pyruvate in a series of enzymatic reactions.
Regarding the second part of your question, it is true that some sources mention 4 ADP molecules as reactants in glycolysis. This might seem confusing at first, but let's dive into the explanation.
ADP stands for adenosine diphosphate, which is an energy-carrying molecule that has lost one of its phosphate groups. In glycolysis, glucose is converted into pyruvate through a series of reactions, and during these reactions, multiple molecules of ATP are generated. ATP (adenosine triphosphate) is formed when ADP undergoes phosphorylation, which involves the addition of a phosphate group.
Hence, when we refer to ADP as a reactant in glycolysis, we are specifically referring to the ADP molecules that will be phosphorylated to form ATP. Since each ATP molecule is composed of one adenosine nucleotide and three phosphate groups, which are obtained from ADP and inorganic phosphate (Pi), it requires four ADP molecules to generate four ATP molecules.
To summarize, during glycolysis, glucose is a reactant that gets converted into pyruvate, and ADP molecules are considered reactants because they undergo phosphorylation to generate ATP.