Definitions:

Term used to describe a protein that consists of two or more non-identical subunits

A term used to describe a protein that consists of two or more identical subunits 

Alternative forms of a gene that occupies a specific position (locus) on a chromosome.

Chemically distinct end of a peptide, polypeptide or protein that has a free amino (—NH2) group (cf. carboxy terminus). Usually abbreviated to N-terminus.

A triplet of bases in a transfer RNA (tRNA) molecule that undergoes base-pairing to a complementary triplet of bases (a codon) in mRNA during protein translation.

Refers to the opposing arrangement of the two complementary strands of a double-stranded DNA molecule, such that one strand runs 3' to 5' and the other 5' to 3'. In proteins it refers to adjacent parts of a polypeptide chain that run in opposite directions.

The cycle of events that take place in a cell leading to its growth and division.

The one way flow of genetic information from DNA via RNA to protein. First proposed by Francis Crick in 1958.

A triplet of nucleotides in mRNA that encodes an amino acid in a polypeptide gene product.

DNA is comprised of two strands of DNA that are held together by hydrogen bonding between bases in opposite strands. The specificity of the base pairing implies that the sequence of bases in one strand can be determined by the sequence of bases in the other i.e. they are complementary.

A cell or organism having two sets of chromosomes (usually, one set contributed by the mother and the other set contributed by the father). A diploid cell is also sometimes referred to as 2n (where n denotes one copy of all the chromosomes).

Refers to a gene allele that determines phenotype in a heterozygous cell or organism, masking the effect of any recessive alleles of the same gene that may be present.

Cells which contain a nucleus, within which lie the chromosomes (genetic material), and a number of other types of membrane-bound organelles. The organisms which contain these cells are known as eukaryotes.

The process by which information from a gene is used to synthesise a functional gene product; a protein or an RNA.

A cell or organism having one set of chromosomes. A haploid cell is also sometimes referred to as n (where n denotes one copy of all the chromosomes).

Cell division that results in the production of haploid daughter cells with half the number of chromosomes of the parent cell i.e. the production of haploid gametes.

A type of RNA that acts as an intermediary in transferring the genetic information from DNA during protein synthesis; mRNA is translated at the ribosome to specify the sequence of amino acids in a polypeptide chain.

Cell division that results in the production of diploid daughter cells with the same number of chromosomes as the parent cell.

The most prominent organelle, which houses the chromosomes and is the site of transcription of DNA into RNA.

The characteristics of an organism often used to describe its biochemical characteristics, i.e. the proteins that it expresses, but also sometimes used to describe its morphological or physiological characteristics.

A sequence of amino acids joined together in a linear chain.

The highest level of organisation of protein structure; refers to the arrangement of the subunits in a multimeric protein.

Refers to a gene allele whose phenotype is not manifest in a heterozygote if it is masked by the presence of a dominant allele. A recessive phenotype will only be expressed in a homozygote carrying two copies of the recessive allele.

Heterotrophs growing and producing biomass by metabolising carbon-based compounds derived from other organisms in an ecosystem.

Body cells that are not germ cells in multicellular eukaryotes. In most cases somatic cells are diploid.

The lowest rank of taxonomy (the basic unit of classification). A population of organisms that have similar characteristics and often (but not always) are able to breed with each other to produce fertile offspring.

A single polypeptide component of a multimeric protein (a protein composed of more than one polypeptide). The arrangement of subunits in a multimeric protein is referred to as quaternary structure.

Term used to describe the arrangement of secondary structures in a folded polypeptide.

The process of making an RNA copy of genetic information stored in DNA. Using one DNA strand as a template, RNA polymerase adds ribonucleotides to the RNA chain according to the rules of complementary base-pairing.

The process of protein synthesis that occurs at the ribosome; the information in an mRNA is used to specify the sequence of amino acids in the polypeptide chain.

A diploid cell produced by the fusion of two haploid gametes during sexual reproduction.