4ATP and Enzymes
An important characteristic of organisms is their ability to derive energy from substances available in the environment surrounding them through metabolism and engage in activities such as walking and exercise. Furthermore, metabolites such as ATP and NADH (or NADPH) are used to derive energy. Intracellular metabolism is catalyzed by enzymes. Enzymes act on a specific substrate and catalyze a specific reaction. Their activity is regulated by various substances. Intracellular actions of enzymes are controlled by their localization and regulation of their activities. This chapter describes the basic intracellular metabolism, ATP and NAD(P)H flow, and basic characteristics of enzymes.