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O

Okazaki fragment

[DNA]

OKT3

More

Olfaction

the sense of smell [Discussion]

Oligonucleotide

A short polymer of, for example, 20 or so deoxyribonucleotides or ribonucleotides; thus a fragment of DNA or RNA.

Oncogene

Gene that contributes to converting a normal cell into a cancer cell. [Discussion]

Oncogenic

Cancer causing.

Open Reading Frame (ORF)

DNA sequence beginning with ATG and read in triplets until it ends with a STOP codon. An ORF is potentially able to encode a polypeptide.

Operator

The DNA sequence in prokaryotes to which a repressor or activator protein binds, turning on (or off) transcription of the associated structural genes of the operon. Located close to the promoter.

Operon

A set of adjacent structural genes and the operator that controls them. [lac operon]

Opiate

A narcotic material prepared or derived from opium. [Discussion]

Opsin

The protein part of the visual pigments of the eye. [More]

Organ

Group of tissues that performs a specific function for an animal or plant (e.g., stomach, leaf).

Organelle

Specialized part of a cell (e.g., mitochondrion) analogous to an organ.

Organic

Term describing all compounds whose molecules contain carbon, with a few exceptions such as carbon dioxide and carbonates.

Organism

Individual living being.

Organizer

[in frog embryology]

Osmosis

Diffusion of a solvent, water in biological systems, through a membrane. [Discussion]

Osmotic pressure

[in guard cells of leaf]

Osteogenesis imperfecta

Osteomalacia

Osteoporosis

and calcium

Ovulation

Release of one or more eggs from the ovary. [role of hormones in]

Ovule

Megasporangium found within the ovary of a seed plant. After fertilization of the egg inside, it develops into a seed. [Discussion]

Oxidation

Process of removing electrons from a substance.[in mitochondria]

Oxygen

Transport by blood

Oxytocin

Ozone

Highly active form of oxygen (O₃ instead of O₂). [More]