S

Second Messenger: A chemical signal, such as calcium ion or cyclic AMP that relays a hormonal message from a cell's surface to its interior.

Signal Transduction Pathway: A mechanism linking a mechanical or chemical stimulus to a cellular response.

Substrate Level Phosphorylation: The formation of ATP by directly acting transferring a phosphate group to ADP from an intermediate substrate in catabolism.

Synapse: The locus where one neurone communicates with another neurone in a neural pathway; a narrow gap between a synaptic terminal of an axon and a signal receiving portion (dendrite or cell body) of another neurone or effector cell. Neurotransmitter molecules released by synaptic terminals diffuse across the synapse, relaying messages to the dendrite or effector.

Synaptic Terminal: A bulb at the end of an axon in which neurotransmitter molecules are stored and released.

T

Transcription: The transfer of information from a DNA molecule into an RNA molecule.

Transcription Factor: A regulatory protein that binds to DNA and stimulates transcription of specific genes.

Transfer RNA (tRNA): An RNA molecule that functions as an interpreter between nucleic acid and protein language by picking up specific amino acids and recognising the appropriate codons in the mRNA.

U