Nucleoid

An aggregation of DNA found in prokaryotes and in the mitochondria and chloroblasts of eukaryotes, and which has some resemblance to a nucleus, but lacks a nuclear envelope and histones.  A chloroblast is the place in a cell where photosynthesis takes place.    See DNA (deoxyribonucleic acid), Eukaryote cell (or organism), Histone, Mitochondria, Nucleus (of a …

Nucleotide

An organic molecule consisting of a purine (adenine or guanine) or a pyramiding (thymine, uracil or cytosine) base linked to a sugar (deoxyribose or ribose) and a phosphate group.  DNA and RNA are made of long chains of nucleotides.  See Adenine, Adenosine triphosphate (ATP), Copy errors, Cytosine, Deoxyribose, DNA (deoxyribonucleic acid), DNA double helix, Guanine, …

Notochord

A term devised by Richard Owen (1804-1892) in 1848, it is an axial mesodermal tissue, adjacent to the neural tube, found in embryonic stages of all chordates and protochordates, and which often regresses as maturity is approached. Typically, it is a rod-shaped mass of vacuolated cells, lying immediately below the nerve cord and may provide …

Novelty preference

The preference of infants for novel stimuli, characterized, for example, by a longer looking time at a novel stimulus when it is paired with a familiar stimulus in a familiarisation task.  See Habituation, Moderate-discrepancy hypothesis, Numerical identity, Pupillometry, Visual acuity, Violation of expectation technique

Notch

A gene involved in cell fate specification.  It is found in all metazoans and in mammals there are four different notch receptors (NOTCH1-NOTCH4).  Notch signalling in conjunction with other gene encoded proteins plays a crucial role in the development and maintenance of a wide variety of tissues during both embryonic and adult life.  For example, …

Nosology

The classification of disorders based on observable and detectable signs and symptoms on observation and interview, or more generally the study of disorders.  See Disorder, Etiology, Oppositional defiant disorder (ODD), Pathogenesis (or pathogensy), Signs and symptoms