Dictionary of Chemistry [6th Ed.]

glyceraldehyde 3-phosphate

(GALP)A triose phosphate,

CHOCH(OH)CH 2 OPO 3 H 2 , that is an in-

termediate in the *Calvin cycle (see

also photosynthesis) and glycolysis.

glycerate 3-phosphateA phos-

phorylated three-carbon monosac-

charide that is an intermediate in the

*Calvin cycle of photosynthesis and

also in *glycolysis. It was formerly

known as 3-phosphoglycerate or phos-

phoglyceric acid (PGA).

glycerides(acylglycerols) Fatty-acid

esters of glycerol. EsteriÜcation can

occur at one, two, or all three hy-

droxyl groups of the glycerol mol-

ecule producing mono-, di-, and

triglycerides respectively. *Triglyc-

erides are the major constituent of

fats and oils found in living organ-

isms. Alternatively, one of the hy-

droxyl groups may be esteriÜed with

a phosphate group forming a phos-

phoglyceride (see phospholipid) or to

a sugar forming a *glycolipid.

glycerineSee glycerol.

glycerol (glycerine; propane-

1,2,3,-triol)A trihydric alcohol,

HOCH 2 CH(OH)CH 2 OH. Glycerol is a

colourless sweet-tasting viscous liq-

uid, miscible with water but insolu-

ble in ether. It is widely distributed

in all living organisms as a con-

stituent of the *glycerides, which

yield glycerol when hydrolysed.

glycerophospholipids See phos-

pholipids.

glycineSee amino acid.

glycobiologyThe study of carbo-

hydrates and carbohydrate com-

plexes, especially *glycoproteins.

glycogen(animal starch) A *poly-

saccharide consisting of a highly

branched polymer of glucose occur-

ring in animal tissues, especially in

liver and muscle cells. It is the major

store of carbohydrate energy in ani-

mal cells and is present as granular

clusters of minute particles.

glycogenesisThe conversion of

glucose to glycogen, which is stimu-

lated by insulin from the pancreas.

Glycogenesis occurs in skeletal mus-

cles and to a lesser extent in the

liver. Glucose that is taken up by

cells is phosphorylated to glucose 6-

phosphate; this is converted succes-

sively to glucose 1-phosphate, uridine

diphosphate glucose, andÜnally to

glycogen. Compare glycogenolysis.

glycogenolysisThe conversion of

glycogen to glucose, which occurs in

the liver and is stimulated by

glucagon from the pancreas and

adrenaline from the adrenal medulla.

These hormones activate an enzyme

that phosphorylates glucose mol-

ecules in the glycogen chain to form

glucose 1-phosphate, which is con-

verted to glucose 6-phosphate. This is

then converted to glucose by a phos-

phatase enzyme. In skeletal muscle

glycogen is degraded to glucose 6-

phosphate, which is then converted

into pyruvate and used in ATP pro-

duction during glycolysis and the

Krebs cycle. However, pyruvate can

also be converted, in the liver, to glu-

cose; thus muscle glycogen is indi-

rectly a source of blood glucose.

Compare glycogenesis.

glycol See ethane-1,2-diol.

glycolic acid (hydroxyethanoic

acid)A colourless crystalline com-

pound, CH 2 (OH)COOH; m.p. 80°C. It

occurs in sugar cane and sugar beet,

and is made by the electrolytic re-

duction of oxalic acid or by boiling a

solution of sodium monochloro-

ethanoate. Glycolic acid is used in

making textiles and leather and for

cleaning metals.

glycolipidAny of a group of sugar-

containing lipids, in which the lipid

glyceraldehyde 3-phosphate 248

g