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acetyl CoA

the entry compound for the citric acid cycle in cellular respiration, formed from a fragment of pyruvate attached to a coenzyme.

aerobic respiration

A catabolic pathway that consumes oxygen (O2) and organic molecules, producing ATP. This is the most efficient catabolic pathway and is carried out in most eukaryotic cells and many prokaryotic organisms.

alcohol fermentation

Glycolysis followed by the conversion of pyruvate to carbon dioxide and ethyl alcohol.

anabolic pathway

A metabolic pathway that consumes energy to synthesize a complex molecule from simpler compounds.

anaerobic respiration

The use of inorganic molecules other than oxygen to accept electrons at the "downhill" end of electron transport chains.

ATP synthase

A complex of several membrane proteins that provide a port through which protons diffuse. This complex functions in chemiosmosis with adjacent electron transport chains, using the energy of a hydrogen ion (proton) concentration gradient to make ATP. ATP synthases are found in the inner mitochondrial membrane of eukaryotic cells and in the plasma membrane of prokaryotes.

beta oxidation

A metabolic sequence that breaks fatty acids down to two-carbon fragments that enter the citric acid cycle as acetyl CoA.

catabolic pathway

A metabolic pathway that releases energy by breaking down complex molecules to simpler compounds

cellular respiration

the catabolic pathways of aerobic and anaerobic respiration, which break down organic molecules for the production of ATP


An energy-coupling mechanism that uses energy stored int he form of a hydrogen ion gradient across a membrane to drive cellular work, such as the synthesis of ATP. Most ATP synthesis in cells occurs by _____.

citric acid cycle

a chemical cycle involving eight steps that completes the metabolic breakdown of glucose molecules begun in glycolysis by oxidizing pyruvate to carbon dioxide; occurs within the mitochondrion in eukaryotic cells and in the cytosol of prokaryotes; the second major stage in cellular respiration.


an iron-containing protein that is a component of electron transport chains in the mitochondria and chloroplasts of eukaryotic cells and the plasma membranes of prokaryotic cells

electron transport chain

a sequence of electron carrier molecules (membrane proteins) that shuttle electrons during the redox reactions that release energy used to make ATP.

facultative anaerobe

an organism that makes ATP by aerobic respiration if oxygen is present but that switches to anaerobic respiration or fermentation if oxygen is not present


a catabolic process that makes a limited amount of ATP from glucose without an electron transport chain and that produces a characteristic end product, such as ethl alcohol or lactic acid


the splitting of glucose into pyruvate. Glycolysis occurs in almost all living cells, serving as the starting point for fermentation or cellular respiration.

lactic acid fermentation

Glycolysis followed by the conversion of pyruvate to lactate with no release of carbon dioxide


Nictinamide adenine dinucleotide, A coenzyme that can accept an electron and acts as an electron carrier in the electron transport chain

obligate anaerobe

an organism that only carries out fermentation or anaerobic respiration. Such organisms cannot use oxygen and in fact may be poisioned by it.


the loss of electrons from a substance involved in a redox reaction

oxidative phosphorylation

the production of ATP using energy derived from the redox reactions of an electron transport chain; the third major stage of cellular respiration

oxidizing agent

the electron acceptor in a redox reaction

proton-motive force

the potential energy stored in the form of an electrochemical gradient generated by the pumping of hydrogen ions across a biological membrane during chemiosmosis

reducing agent

the electron donor in a redox reaction


the addition of electrons to a substance involved in a redox reaction

substrate-level phosphorylation

the formation of ATP by an enzyme directly transferring a phosphate group to ADP from an intermediate substrate in catabolism

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