Exergonic reactions have a negative G and energy is released. Occur when energy released by exergonic reaction is used to drive an endergonic reaction. ATP is a nucleotide made of base adenine, sugar ribose, and three phosphate groups. Metabolic energy is captured more easily if it is released in small increments. Each step in a series of chemical reactions is assisted by an enzyme.
Enzymes are catalysts that speed chemical reactions without the enzyme being changed.
Every enzyme is specific in its action and catalyzes only one reaction or one type of reaction. A substrate is a reactant in an enzymatic reaction. Almost no metabolic reaction occurs in a cell unless its own enzyme is present. Without enzymes, activation is achieved by heating reaction flask to increase molecular collisions. If reactants can form more than one product, enzymes present determine product produced.