Glossary

An A-Z of keywords and phrases, all of which are relevant to the post-16 biology curriculum.

 

A B C D E F G H I J K L M N O P Q R S T U V W Y Z
T cells

Named after the thymus, the organ where T cells mature. T cells have a protein called the T cell receptor on their surface. Types include helper T cells, cytotoxic T cells and regulatory T cells. A type of lymphocyte.

Target

The molecule that a drug acts on.

Telomere

Telomeres are located at the end of eukaryotic chromosomes and act as protective caps.

Temporal lobe

The part of the brain that contains specialised areas for processing sound, language and memory. It is involved in cognitive functions such as mood, appetite, sleep and learning.

Tertiary structure

The unique three-dimensional shape that a protein takes. The shape is held together by interactions between the side chains of amino acids, including hydrogen bonds, disulphide bonds, ionic and hydrophobic interactions, and van der Waals forces.

Testosterone

A steroid hormone, and the principal male sex hormone. It is produced by the testes in men and by the ovaries, in much smaller quantities, in women. It initiates the development of male reproductive organs during early development and stimulates sperm production in adult males.

Thermogenesis

The production of heat in the body.

Thigmotropism

Movement or growth in plants in response to touch.

Thymus

A gland found behind the breastbone. It is where T cells mature.

Tissue(s)

A collection of similar cells that work towards a shared function.

Tolerance

The decrease in a person’s reaction to a drug that may come with prolonged use of it – requiring an increase in dose to achieve the same effect.

Totipotent

A term used to describe cells that can divide and produce all of the other cells of an organism (as well as placental cells). Cells with this ability are very rare in animals (occurring only at the zygote stage), but are common in plants.

Trans

A molecular arrangement in which two particular atoms or groups are found on the opposite side of a double bond. For example, in a particular unsaturated fatty acid, the hydrogens can be on the opposite sides of the carbon–carbon double bond (trans) or on the same side (cis).

Trans fat

A certain way of processing vegetable oils produces what are known as trans fats, or partially hydrogenated oils, which extend the shelf-life of foods they are added to. Trans fats have some carbon–carbon double bonds in the trans position. Eating a diet high in trans fats is linked to cause heart disease, diabetes and stroke. Trans fats occur naturally at low levels in some meat and dairy products.

Transcription

The process in which a length of DNA is copied into messenger RNA (mRNA) by the enzyme RNA polymerase.

Transcription factors

Proteins involved in the process of transcription – often activating this process.

Translation

The process of using the genetic information in mRNA to make a protein chain from amino acids. This is performed by ribosomes.

Triglyceride

An unreactive lipid consisting of one glycerol molecule bonded to three fatty-acid molecules. When dietary fat is digested, triglycerides are produced and stored in adipocytes (fat cells).

tRNA (transfer RNA)

The key adaptor molecules needed for translation. Each tRNA molecule recognises a particular codon and ensures the correct amino acid is brought to the ribosome’s active site for protein synthesis.

Tropomyosin

A key protein in muscle contraction. It prevents contraction by binding to actin, stopping it from binding to myosin.

Troponin

A globular protein which moves tropomyosin to allow binding between actin and myosin in muscle contraction.

Troposphere

The layer of the Earth’s atmosphere closest to the ground, where greenhouse gases are found. Ozone in the troposphere contributes significantly to global warming.

Tumour

An abnormal mass of tissue that occurs because of uncontrolled cell division. Tumours can be benign (not cancerous) or malignant (cancerous).

Tumour necrosis factor (TNF)

A chemical made by macrophages and some other immune cells. It has an important role in the immune system, including inducing fever, inflammation and programmed cell death.

Turgor pressure

The pressure inside cells with cell walls (such as plant cells) that pushes the plasma membrane up to and against the cell wall.

Twin studies

Studies looking at non-identical and identical twins, raised together or apart, to determine the environmental and genetic factors involved in their specific development.