Metabolism and Energy Pathways


acetyl-coenzyme A

coenzyme complex that holds acetate from pyruvate so it can be oxidized in the citric acid cycle. It also has roles in fatty acid synthesis and other biological processes.

activation energy

minimum energy needed for a chemical reaction to initiate

active site

place on an enzyme where the substrate binds and the reaction occurs

adenosine triphosphate (ATP)

biological unit of energy, which consists of an adenosine (an adenine group and a ribose sugar) and three phosphate groups

aerobic respiration

chemical process in which energy is produced in the presence of oxygen


functional in both catabolic (breaking down molecules to produce energy) and anabolic (building complex compounds that require energy) directions


sequence of chemical reactions that constructs or synthesizes molecules from smaller units


inactive enzyme that requires a cofactor for activation


organism that can make its own food

beta oxidation

catabolic process that breaks down fatty acids to produce acetyl-CoA, NADH, and FADH2


sequence of chemical reactions that breaks down or decomposes molecules into smaller units while generating energy


substance that causes the rate of a chemical reaction to increase

citric acid cycle

series of chemical reactions used by all aerobic organisms to release ATP


nonprotein chemical, such as NAD and FAD, that helps an enzyme function


nonprotein compound or metallic ion whose presence is essential for the activity of an enzyme


alteration of a protein's shape through some form of external stress, resulting in lack of function

electron transport chain

series of electron transporters that move electrons from NADH and FADH2 to oxygen molecules; protons are pumped from the mitochondrial matrix to the intermembrane space, and oxygen is reduced to form water


substance, usually a protein, that speeds up a biological reaction without being consumed in the reaction


anaerobic breakdown of a substance, such as glucose, that produces a limited amount of ATP for a cell


metabolic pathway in which glucose is broken down into pyruvate in the cytoplasm of the cell


organism that obtains energy and carbon from consuming other organisms


active form of an enzyme that is a complex resulting from the combination of an enzyme and the necessary cofactor(s)


sum of biological process that builds or breaks molecules to provide cells with the capacity to acquire and utilize energy

oxidative phosphorylation

production of ATP through chemiosmosis in the mitochondria through an electron transport chain


process by which autotrophs convert light energy into chemical energy that is stored in organic compounds such as sugars

proton gradient

pathway in which protons move from an area of higher concentration to an area of lower concentration

redox reaction

reaction that involves the transfer of electrons between two atoms or molecules


molecule that is acted upon by an enzyme by binding to the enzyme's active site