NAD+
= Nicotinamide adenine dinucleotide.
Na/K-ATPase
pump Primary active transport protein that splits ATP and releases
energy used to transport sodium out of cell and potassium in.
Natural
killer (NK) cells A group of lymphocytes which have the intrinsic
ability to recognize and destroy some virally infected cells and some
tumor cells by binding nonspecifically to virus-infected and cancer cells.
No prior exposure to the antigen is required.
Neoplasm
Cancerous tissue
Nernst
equation Mathematical expression that defines the electric potential
E across a membrane as directly proportional to the logarithm of the ratio
of the ion concentrations on either side of the membrane and inversely
proportional to the valency of the ions.
Neuroeffector
junction Synapse between a neuron and muscle or gland cell.
Neurohormone
Chemical messenger that is released by a neuron and travels in bloodstream
to its target cell.
Neuropeptide
A peptide secreted by neurons that functions as a signaling molecule either
at a synapse or elsewhere. These molecules have diverse, often long-lived
effects in contrast to neurotransmitters.
Neurotransmitter
Extracellular signaling molecule that is released by the presynaptic neuron
at a chemical synapse and relays the signal to the postsynaptic cell.
A neurotransmitter can elicit either an excitatory or inhibitory response,
but the response, but the response is determined by the receptor activated
by the neurotransmitter not by the chemical nature of the neurotransmitter.
Examples include acetylcholine, dopamine, GABA (γ-aminobutyric acid),
and serotonin.
Nick
A single-strand break, involving the absence of one or more nucleotides,
in a double-stranded DNA molecule.
Nick translation
The repair of a nick with DNA polymerase I, usually to introduce labeled
nucleotides into a DNA molecule.
Nicotinamide
adenine dinucleotide (NAD+) Coenzyme derived from
the B vitamin niacin that transfers hydrogen from one substrate to another.
Neoplastic
A new, unnecessary proliferation of cells giving rise to a tumor.
Neoplastic
transformation The conversion of a nontumorigenic cell into a tumorigenic
cell.
Northern
translation The repair of a nick with DNA polymerase I, usually to
introduce labeled nucleotides into a DNA molecule.
Nothern
transfer A technique for transferring bands of RNA from an agarose
gel to a nitrocellulose or similar membrane.
Nude mouse
A genetically athymic mouse which also carries a closely linked gene producing
a defect in hair production.
Nucleic
acid hybridization Formation of a double-stranded molecule by base-pairing
between complementary or homologous polynucleotides.
Nucleolus
Large structure in the nucleus of eukaryotic cells where rRNA synthesis
and processing occurs and ribosome subunits are assembled.
Nucleosome
Small structural unit of chromatin consisting of a disk-shaped core of
histone proteins around which a ~146-bp segment of DNA is wrapped.