Isoaccepting tRNAs
tRNA molecules that carry the same amino acid.

Isoalleles
Different forms of a gene that give rise to the same phenotype or very similar phenotypes.

Isoantibody
An antibody capable or reacting with an antigen derived from a member of the same species as that in which it is raised.

Isoantigen (alloantigen)
An antigen produced only by some members of a species that elicits an immune response in individuals who lack the antigen. Blood group antigens are alloantigens.

Isocaudomers
Restriction endonucleases that recognise different sequences but cleave in such a way to create identical termini. For example, the five members of the Bam HI family generate the same 5’GATC3’ from different sequences.

Isochromosome
A chromosome containing two identical arms and identical genes. The arms are mirror images of each other.

Isocratic elution
See simple elution.

Isoelectric focusing
Separation of proteins by electrophoresis in a pH gradient such that each protein moves until it reaches its isoelectric point where it becomes stationary.

Isoelectric pH
The pH at which an amino acid or protein has no net charge. At this pH, the molecule does not move in an electric field.

Isoeletric point
The pH at which a protein has no net charge.

Isoenzymes (isozymes)
Multiple forms of an enzyme that catalyse the same reaction but differ from each other in their amino acid sequence and/or kinetic and regulatory properties.

Isoform
A member of a family of closely related proteins that have some amino acid sequences in common while others are different.

Isogamy
Sexual reproduction involving the fusion of gametes that are similar in size and structure.

Isogene
The variants or mutations within the gene of a patient population.

Isogenic
Of the same genotype.

Isogenic stocks
Strains of organisms that are genetically identical; homozygous.

Isograft
A tissue transplanted between two genetically identical individuals.

Isohaemagglutinins
Antibodies to major erythrocyte antigens in bacteria, food, etc.

Isolated system
A system in which there is no exchange of mass or energy between the system and its surroundings.

Isolation medium
An optimum medium that is suitable for explant survival, growth and development.

Isoleucine
A branched chain amino acid.

Isomerase
An enzyme catalyzing an intramolecular rearrangement.

Isomerisation
Rearrangement of atomic groups within the same molecule without gain or loss of atoms.

Isomers
Enzymes that catalyse transfer of compounds to their positional isomers.

Isomorphism
Similarity of crystal shape, unit cell dimensions and structure between substances of similar but not identical chemical composition.

Isoniazed (isonicotinic acid hydrazide, INH)
An antivitamin of B6 used as an antituberculosis drug. It causes deficiency manifestations of niacin with pellagra-like symptoms. It forms a hydrazone complex with pyridoxal phosphate, promoting its excretion. High doses of INH can cause neurological changes and alterations in tryptophan metabolism.

Isoosmotic
See isotonic.

Isoploid
Even numbers of chromosome sets.

Isoprene
The hydrocarbon 2-methyl-1,3-butadiene that serves as a precursor for many lipid molecules.

Isoprenoid
Natural products formed by enzymatic polymerization of two or more isoprene units. Also called terpenoids.

Isopycnic centrifugation
A centrifugation technique that depends only on the buoyant density of the particle and not on its shape or size.

Isoschizomers
Two different restriction enzymes that recognise the same DNA sequence and cut at the same site; e.g. Smal and Xmal, which recognize and cut the sequence CCCGGG.