Apoptosis (also known as Programmed cell death) – the natural process of cell suicide common to multicellular organisms, which is critical for healthy growth and protection against disease. Apoptosis plays a role in shaping the developing embryo, for example, as digits form, cells in the interstices are effectively binned. When a cell is diseased or faulty, apoptosis is triggered helping to combat the spread of disease. The process may be initiated via a number of signalling pathways. e.g. TNF and TRAIL bind to their specific receptor on the surface of a cell, which initiates a cascade of internal signalling events that can result in apoptosis as a response.

DNA (deoxyribonucleic acid) – the stuff of our genes. The DNA double helix combines two long chains of organic bases of four kinds (adenine: A, guanine: G, cytosine, C and thymine: T) along a regular sugar-phosphate backbone. Along its length A always pairs with T, and C with G. The ladder-like molecule – twisted into its characteristic helix - may be billions of base-pairs long and is packaged up (some 2m in humans) within the nucleus of the cell.

Gene – a part of the genome that contains the information necessary to make a working molecule within the cell. DNA is transcribed into RNA (which mirrors its sequence of bases). mRNA transcripts may leave the nucleus to be translated into functional protein. Genes in higher organisms tend to have control regions allowing genes to be switched on or off by proteins.

Gene expression – the process whereby a gene is making mRNA and then subsequently protein (see Gene)

Genome – the entire sum of genes within a species.

Hybridisation – organic bases within DNA (adenine: A, guanine: G, cytosine: C and thymine: T) have specific affinities for each other: A always pairs with T and C with G. Free organic bases will hybridise to a sequence based on these affinities. A sequence of AAATCGG will hybridise to TTTAGCC and vice-versa.

Ligand – a free-floating molecule that binds to a protein receptor triggering a signalling pathway.

Metastases – the spread of disease from one body organ or tissue to other body regions as occurs in cancer.

Microarray – a lab-on-a-chip that allows scientists to assay biological sets such as the genome (sum of all our genes) or the proteome (sum of all proteins within a cell). While genes are identical between cells, their activity and the resultant protein complement of a cell is varied. A genome microarray allows scientists to see whether each of the 20 000 genes is switched on or off at any one time. A proteome microarray allows scientists to see which (of all possible proteins) proteins a cell is making at a certain point in time. The microarray plate contains probes for all the genes or proteins, to which actually genetic or protein fragments can bind.

Mutation – a heritable alteration of DNA sequence(s), chromosome parts or chromosome numbers in a cell either spontaneous or chemically induced or as a result of a mistake in the replication of the genetic code or in meiosis/mitosis, which may alter the characteristics of the organism.

Natural killer cells – a type of white blood cell that plays an important role in eliminating tumour cells and cells infected with viruses.

NFkappaB (nuclear factor kappa-light-chain-enhancer of activated B cells) – a protein that plays a key role in regulating the immune response to infection. Present in most cells, NfkappaB controls the transcription of genes.

Organic base – a class of weakly alkaline organic molecules that usually contain nitrogen. DNA contains four kinds: adenine (A), cytosine (C), guanine (G) and thymine (T). In the DNA double helix A always pairs with T, and C with G. RNA contains the same organic bases, except for thymine. RNA substitutes uracil (U) for thymine.

Programmed cell death (see Apoptosis)

Protease inhibitor – a class of drugs that are used to treat or prevent viral infection, e.g. HIV and Hepatitis C. The inhibitor blocks the action of the viral enzyme, protease, which effectively blocks viral replication within cells.

Protein – a complex of polypeptide chains. Polypeptides are long chains of amino-acids encoded for by sequences of DNA. A sequence of three bases (triplet codon) specifies one amino acid.

Receptor – a protein molecule that specifically responds to a ligand. Ligand binding elicits a signalling cascade resulting in changes in gene expression within the cell.

Reverse transcriptase – an enzyme that makes double-stranded DNA from single-stranded RNA. Retroviruses like HIV have the enzyme and use it to incorporate their genome (which is made from RNA) into the host.

RNA (ribonucleic acid) – one of two major forms of nucleic acid. RNA conveys information within DNA into protein. RNA faithfully reproduces DNA sequences into single-stranded molecules with adenine (A), cytosine (C), guanine (G) and uracil (U) instead of thymine (T). Some viruses e.g. HIV have RNA genomes.

RNAi technology – one of several means of silencing genes. Small RNA molecules within cells naturally regulate gene expression. Experimentally sequence specific RNAs can be made to intercept mRNA transcripts encoded by DNA before they can be translated into protein. With the help of an intracellular machinery they induce cleavage and destruction of their target mRNAs.

Signalling cascade – a network of interacting components (genes, proteins and metabolites) that governs a specific process or processes within the cell.

TRAIL (TNF-related apoptosis-inducing ligand) – a protein that acts as a ligand. By binding to its receptor, TRAIL initiates the process of apoptosis.

Transcriptome – the set of all RNA molecules produced by a cell type.

TNF (tumour necrosis factor) – a group of proteins that can cause cell death, but can also regulate cell proliferation and differentiation. TNF is the founding member of this cytokine family.