Chapter 9 Vocabulary

Beta oxidation

Beta oxidation

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

proton-motive force (prō′-ton)

The potential energy stored in the form of a proton electro- chemical gradient, generated by the pumping of hydrogen ions (H+) across a biological membrane during chemiosmosis.

redox reaction (rē′-doks)

A chemical reac- tion involving the complete or partial transfer of one or more electrons from one reactant to another; short for reduction-oxidation reaction.

reducing agent

The electron donor in a redox reaction.

Reduction

The complete or partial addition of electrons to a substance involved in a redox reaction

substrate-level phosphorylation

The enzyme-catalyzed formation of ATP by direct transfer of a phosphate group to ADP from an intermediate substrate in catabolism.

lactic acid fermentation

Glycolysis followed by the reduction of pyruvate to lactate, re- generating NAD+ with no release of carbon dioxide.

NAD+ Nicotinamide adenine dinucleotide

a coenzyme that cycles easily between oxidized (NAD+) and reduced (NADH) states, thus act- ing as an electron carrier.

obligate anaerobe (ob′-lig-et an′-uh-rōb)

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

Oxidation

The complete or partial loss of elec- trons from a substance involved in a redox reaction.

oxidative phosphorylation (fos′-fōr-uh-lā′- shun)

The production of ATP using energy derived from the redox reactions of an elec- tron transport chain; the third major stage of cellular respiration.

oxidizing agent

The electron acceptor in a re- dox reaction

cytochrome (sī′-tō-krōm)

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 elec- tron carrier molecules (membrane proteins) that shuttle electrons down a series of redox reactions that release energy used to make ATP.

facultative anaerobe (fak′-ul-tā′-tiv an′-uh- rōb)

An organism that makes ATP by aero- bic respiration if oxygen is present but that switches to anaerobic respiration or fermenta- tion if oxygen is not present.

Fermentation

A catabolic process that makes a limited amount of ATP from glucose (or other organic molecules) without an electron trans- port chain and that produces a characteristic end product, such as ethyl alcohol or lactic acid.

glycolysis (glī-kol′-uh-sis)

A series of reactions that ultimately splits glucose into pyruvate. Glycolysis occurs in almost all living cells, serving as the starting point for fermentation or cellular respiration.

acetyl CoA

Acetyl coenzyme A; the entry com- pound for the citric acid cycle in cellular respi- ration, formed from a two-carbon fragment of pyruvate attached to a coenzyme.

aerobic respiration

A catabolic pathway for organic molecules, using oxygen (O2) as the final electron acceptor in an electron trans- port chain and ultimately 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 reduction of pyruvate to ethyl alcohol, regenerating NAD+ and releasing carbon dioxide.

ATP synthase

A complex of several membrane proteins that functions in chemiosmosis with adjacent electron transport chains, using the energy of a hydrogen ion (proton) concentra- tion gradient to make ATP. ATP synthases are found in the inner mitochondrial membranes of eukaryotic cells and in the plasma mem- branes of prokaryotes.

cellular respiration

The catabolic pathways of aerobic and anaerobic respiration, which break down organic molecules and use an electron transport chain for the production of ATP.

chemiosmosis (kem′-ē-oz-mō′-sis)

An energy- coupling mechanism that uses energy stored in the form of a hydrogen ion gradient across a membrane to drive cellular work, such as the synthesis of ATP. Under aerobic condi- tions, most ATP synthesis in cells occurs by chemiosmosis.

citric acid cycle

A chemical cycle involving eight steps that completes the metabolic breakdown of glucose molecules begun in gly- colysis by oxidizing acetyl CoA (derived from pyruvate) to carbon dioxide; occurs within the mitochondrion in eukaryotic cells and in the cytosol of prokaryotes; together with pyruvate oxidation, the second major stage in cellular respiration.