Okazaki fragment

Small fragments of DNA, which are joined together by ligases during DNA replication.

Oncology

The study and treatment of cancer.

Opiate

A drug derived from the opium poppy, for example morphine, opium and heroin.

Optimise

Modify to achieve maximum efficiency.

Optimum

The best or maximum that can be achieved.

Organic

A substance made up of two or more atoms of carbon. It also refers to products that have been grown without artificial fertilisers or pesticides.

Organic chemistry

A branch of chemistry specialising in the structure, properties and reactions of molecules made mostly from carbon and hydrogen atoms.

Organic molecule

A molecule that consists mainly of carbon and hydrogen atoms. Examples include carbohydrates, lipids and nucleic acids.

Organisation for Economic Co-operation and Development (OECD)

An international organisation providing information on trade, economics, education, development and science. It has 30 member countries including New Zealand, Australia, the USA and Japan.

Osmosis

The movement of water from a region of high concentration to a region of low concentration through a semi-permeable membrane.

Ovulation

The release of a gamete or egg cell in female animals.

Oxidant

A chemical substance that causes the oxidation (loss of electrons) of another chemical substance.

Oxidation

Reaction that causes a molecule to loose electrons (Reacting with oxygen is a common way for this to happen).

Oxidative damage

Damage to cells caused by reactive oxygen species (ROS); also known as oxidative stress.

Oxidative phosphorylation

A metabolic pathway that uses energy released by the oxidation of nutrients to produce adenosine triphosphate (ATP).

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