Nucleosome
A structure that is responsible in part for the compactness of a chromosome. Each nucleosome consists of a sequence of DNA wrapped around a core of histone, which is a type of protein.
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- Nucleotide
A subunit of DNA or RNA that consists of a nitrogenous base (A, G, T, or C in DNA; A, G, U, or C in RNA), a phosphate molecule, and a sugar molecule (deoxyribose in DNA, and ribose in RNA). Thousands of nucleotides are linked to form a DNA or an RNA molecule.
- Nucleus
1) In cell biology, the structure that houses the chromosomes. 2) In neuroanatomy, a group of nerve cells.
- Nude mouse
A mutant mouse said to be nude because it is hairless due to the presence two copies of the gene “nu” (for nude). Nude mice have no thymus and therefore no T cells, a class of lymphocytes that depend on the thymus to develop. For lack of T cells, nude mice cannot reject tumors or […]
- Null mutation
A mutation (a change) in a gene that leads to its not being transcribed into RNA and/or translated into a functional protein product. For example, a null mutation in a gene that usually encodes a specific enzyme leads to the production of a nonfunctional enzyme or no enzyme at all.
- Nullipara
A woman who has not given birth to a viable child.