Glossary

The words, in plain English

Every term defined here is also underlined the first time it appears in an article, so you can read the definition without leaving the sentence.

40 of 40 terms

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antibiotic: A drug that kills bacteria or stops them multiplying. It has no effect on viruses.
antibiotic resistance: What happens when bacteria that survive a drug pass on the trait, until the drug stops working on that population.
antibody: A Y-shaped protein the immune system makes to lock onto one specific target, such as part of a virus, and mark it for destruction.
antigen: Anything the immune system recognises as foreign and responds to — usually a fragment of a protein on the surface of a microbe.

Cas9: The molecular scissors in the CRISPR system — the enzyme that makes the actual cut in DNA once it has been guided to the right place.
chemotherapy: Drug treatment that kills rapidly dividing cells. It works on cancer for that reason, and causes side effects for the same reason.
clinical trial: A study testing a treatment in people, in stages, under rules designed to show whether it genuinely works and is safe.
CRISPR: A system borrowed from bacteria that can be aimed at a chosen stretch of DNA and cut it, letting researchers disable or replace a gene.

DNA: The molecule that stores genetic instructions, written in four chemical letters and held as two strands twisted around each other.

enzyme: A protein that speeds up one particular chemical reaction without being used up by it.
epidemiology: The study of how often diseases occur in populations, where, and why.

gene: A stretch of DNA that carries the instructions for building one protein, or for controlling when other genes are used.
genome: The complete set of genetic instructions in an organism: every gene, plus the far larger amount of DNA that is not a gene.

immune system: The network of cells and proteins that detects and removes things the body treats as foreign, and that must learn not to attack the body itself.
in vitro: In glass — an experiment done in a dish or tube rather than in a living body.
in vivo: In a living organism, as opposed to in a dish.
incubation period: The gap between catching an infection and first showing symptoms.
invertebrate: An animal without a backbone. Most animal species are invertebrates.

metastasis: When cancer cells leave the original tumour, travel through blood or lymph, and start growing somewhere else.
mitochondria: Compartments inside cells that release energy from food. They carry their own small loop of DNA, inherited only from the mother.
monoclonal antibody: Identical antibodies grown from a single cell line, all aimed at exactly the same target. Used as drugs and as laboratory tools.
mRNA: A short-lived copy of a gene that carries its instructions out to the cell’s protein-building machinery. It is not DNA and it does not enter the nucleus.
mutation: A change in a DNA sequence. Most do nothing at all; a few are harmful, and a few are the raw material of evolution.

pandemic: An epidemic that has spread across several countries or continents.
pathogen: Any organism that causes disease — a bacterium, virus, fungus or parasite.
peer review: The process where other specialists in a field examine a paper before a journal publishes it. It catches obvious errors; it does not guarantee a result is correct.
phylum: A broad grouping in biological classification, sitting below kingdom — all animals with a notochord are one phylum, for instance.
placebo: A dummy treatment given for comparison, so researchers can tell a drug’s real effect from the improvement people show anyway.
plasmid: A small circle of DNA, separate from the main chromosome, that bacteria pass around. Widely used to carry genes into cells deliberately.
preprint: A paper posted publicly before peer review. It may be perfectly sound or completely wrong, and nobody independent has checked yet.
protein: A chain of amino acids folded into a specific shape. Proteins do nearly all the work in a cell — structure, signalling, chemistry.
protein synthesis: The process of reading a gene and assembling the protein it specifies, one amino acid at a time.

RNA: A single-stranded relative of DNA. Cells use it to carry genetic messages, and some viruses use it as their genetic material.

stem cell: A cell that has not yet specialised, and can both renew itself and turn into other cell types.

tissue culture: Growing cells or pieces of tissue in a controlled container rather than in a living organism.
tumour: A mass formed by cells dividing when they should not. Benign ones stay put; malignant ones invade surrounding tissue.

vaccine: A preparation that shows the immune system a harmless likeness of a pathogen, so it can respond quickly to the real one later.
variant: A version of a virus carrying mutations that set it apart from the original, sometimes changing how easily it spreads or how well vaccines work against it.
vector: Anything used to carry genetic material into a cell — often a modified virus or a plasmid. In disease, it instead means the organism that carries an infection, such as a mosquito.
virus: A package of genetic material in a protein coat. It cannot reproduce on its own and must hijack a living cell to make copies.