Respiration and cellular energy definitions

Glycolysis, ATP and the link reaction

ATP

Adenosine triphosphate: a phosphorylated nucleotide made of adenine, ribose and three phosphate groups, used as the immediate source of energy in every cell.

Hydrolysis of ATP

The breaking of the bond to the terminal phosphate by addition of water, catalysed by ATP hydrolase, giving ADP and inorganic phosphate and releasing about 30.5 kJ per mole.

Phosphorylation

The addition of a phosphate group to a molecule. The phosphate released from ATP is often added to another molecule, making it more reactive.

Glycolysis

The splitting of glucose into two molecules of pyruvate in the cytoplasm, producing a net gain of two ATP and two reduced NAD, without oxygen.

Substrate-level phosphorylation

The direct transfer of a phosphate group from a substrate molecule onto ADP, as opposed to ATP made using a proton gradient.

Coenzyme

An organic non-protein molecule that an enzyme needs in order to work. NAD accepts hydrogen from a substrate and carries it elsewhere, so it is a hydrogen carrier.

Oxidation

In respiration, most easily read as the loss of hydrogen. A substrate that hands hydrogen to NAD has been oxidised; the NAD has been reduced.

Link reaction

The oxidative decarboxylation of pyruvate in the mitochondrial matrix, producing carbon dioxide, reduced NAD and a two-carbon acetyl group carried by coenzyme A.

Decarboxylation

Removal of a carboxyl group from a molecule, released as carbon dioxide.

Dehydrogenation

Removal of hydrogen from a molecule, catalysed by a dehydrogenase, with the hydrogen taken up by a coenzyme.

Acetyl coenzyme A

The two-carbon acetyl group attached to coenzyme A, which carries it into the Krebs cycle.

The Krebs cycle and oxidative phosphorylation

Krebs cycle

A closed series of reactions in the mitochondrial matrix in which an acetyl group is combined with a four-carbon acceptor and completely oxidised, releasing carbon dioxide and reducing coenzymes, and regenerating the acceptor.

Dehydrogenase

An enzyme that catalyses the removal of hydrogen from a substrate, passing it to a coenzyme such as NAD or FAD.

Decarboxylase

An enzyme that catalyses the removal of a carboxyl group from a substrate, released as carbon dioxide.

FAD

A hydrogen-carrying coenzyme like NAD, but one that hands its electrons to the transport chain further along, so it yields less ATP per molecule.

Electron transport chain

A series of carrier proteins in the inner mitochondrial membrane that pass electrons from one to the next, releasing energy used to pump protons into the intermembrane space.

Chemiosmosis

The synthesis of ATP driven by the movement of protons down an electrochemical gradient through ATP synthase.

Oxidative phosphorylation

The formation of ATP from ADP and inorganic phosphate using energy from the electron transport chain, with oxygen as the final electron acceptor.

Final electron acceptor

The molecule that takes electrons from the end of the chain. In aerobic respiration it is oxygen, which combines with protons to form water.

Anaerobic respiration and the respiratory quotient

Anaerobic respiration

The release of energy from an organic molecule without oxygen, in which glycolysis continues because reduced NAD is oxidised by a reaction other than the electron transport chain.

Fermentation

The anaerobic conversion of pyruvate to lactate or to ethanol and carbon dioxide, regenerating oxidised NAD.

Respiratory quotient

The volume of carbon dioxide released divided by the volume of oxygen taken in over the same period. Its value indicates the substrate being respired.

Redox indicator

A dye that changes colour when it is reduced or oxidised, such as methylene blue, which is blue when oxidised and colourless when reduced.

Facultative anaerobe

An organism that respires aerobically when oxygen is available and anaerobically when it is not, as yeast does.

Exercise, sports medicine and performance-enhancing drugs

Osteoarthritis

A joint disease in which the articular cartilage is worn away, so that bone surfaces rub, causing pain, swelling and stiffness.

Overtraining

A fall in performance, with persistent fatigue and frequent infections, caused by heavy training without enough recovery.

Causal relationship

A relationship in which a change in one variable brings about the change in the other, rather than both simply varying together.

Keyhole surgery

Surgery carried out through small incisions using a camera on a narrow tube and fine instruments; on a joint it is called arthroscopy.

Prosthesis

An artificial device that replaces a missing or damaged part of the body, such as a joint replacement or an artificial limb.

Anabolic steroid

A drug related to testosterone that enters muscle cells, binds a receptor and switches on genes for muscle protein, increasing muscle mass and strength.

EPO

Erythropoietin, a hormone made by the kidneys that stimulates the bone marrow to produce red blood cells.

Therapeutic use exemption

Permission for an athlete with a diagnosed condition to take a prohibited medicine, provided it only restores normal health.

Utilitarianism

The ethical position that the right action is the one producing the greatest good for the greatest number of people.