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The Basics of Metabolism


active site

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

anabolic reaction

a metabolic reaction that builds complex molecules from simpler molecules and requires energy

catabolic reaction

a metabolic reaction that breaks down complex molecules into simpler molecules and releases energy


the act of a catalyst, such as an enzyme, speeding up a biological reaction

endergonic reaction

a reaction that takes in energy


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


a state in which there is no net change through time; a state when changes will not occur

exergonic reaction

a reaction that releases energy

first law of thermodynamics

scientific law that states that energy cannot be created or destroyed, only transformed from one type of energy to another type of energy

metabolic processes

all of the processes in a cell or living organism that are necessary for life


on a molecular level, the biological processes that build or break molecules; on an organismal level, all of the chemical reactions within an organism that provide cells with the capacity to acquire energy and use that energy to carry out different functions

redox reaction

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


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