N Asparagine in proteins, An
unknown nucleotide in DNA or RNA natural selection the preservation of favorable alleles and the rejection
of injurious ones. Differential reproduction of different
members of a species due to the variability in fitness among
individuals or genotypes, leading to changes in allele
frequencies over time. N-degron An N-terminal amino acid sequence that influences the
degradation of a protein in which it is found negative selection neighboring taxa neighbor joining method A method for construction of phylogenetic trees neutral mutation a mutation that does not change the fitness of the
organism neutral theory The proposal that evolution at the molecular level is
primarily determined by mutational input and random genetic
drift, rather than by natural selection. nick A position in a double-stranded NDA molecule where one of
the polynucleotides is broken due to the absense of a
phosphodiester bond. nick translation A method of labeling DNA with radioactive or other
modified nucleotides by using DNA polymerase I nitrogenous base One of the purines or pyrimidines that form part of the
molecular structure of a nucleotide N-linked glycosylation The attachment of sugar units to an asparagine in a
polypeptide node the graphical representation in a phylogenetic tree of an
extant or ancestral operational taxonomic unit. nondegenerate site A nucleotide site in the coding region at which all
substitutions are nonsynonymous non disjunction the failure of homologous chromosomes to separate during
meiosis non functionalization (silencing) the turning of a functional gene into a pseudogene
following the occurrence of an incapacitating mutation. nongenic DNA the portion of the genome that does not contain genes nonhomologous end joing Another name for the double-strand break repair
process nonpenetrance The situation whereby the effect of mutation is never
observed during the lifetime of a mutant organism nonpolar A hydophobic (water-fearing) chemical group. nonsense codon termination codon. UAG, UAA or UGA. A codon for which no
normal tRNA exists, the presence of which terminates the
process of translation. nonsense mutation A mutation that alters a sense codon in to a termination
codon nonsense strand The transcribed strand of a gene, the sequence of which
is complementary to the RNA transctipt. nonsynonymous substitution missense substitution. A substitution that alters a codon
to that for another amino acid. Northern blotting The transfer of RNA from an electrophoresis gel to a
membrane prior to northern hybridization Northern hybridization A technique used for detection of a specific RNA molecule
against a background of many other RNA molecules. It's
called "Northern" because Edwin Southern first developed
this method of hybridization, only he used DNA. Thus, DNA
blots are called "Southerns". Continuing this naming
strategy, a blotting method using proteins is called
"Western blots". N-terminal the amino terminal end of a protein nuclear genome The DNA molecules present in the nucleus of a eukaryotic
cell NMR Spectroscopy Nuclear Magnetic Resonance- A technique for determining
the structure of molecules containing hydrogen, carbon,
phosphorous or fluorine. It has become an important tool for
determination of the 3D structure of proteins. nucleic acid The original definition was used to describe the acidic
chemical compound isolated from the nuclei of eukaryotic
cells. This term now refers specifically to the polymeric
molecule comprising nucleotide monomers such as DNA and
RNA. nucleic acid hybridization formation of a double-stranded hybrid by base-pairing
between complementary polynucleotides. nucleoid The DNA-containing region of a prokaryotic cell nucleolus The region of the eukaryotic nucleus in which the rRNA
transcription occurs nucleoside A purine (cytosine, uracil or thymine) or pyrimidine
(adenine or guanine) base linked to a pentose. nucleosome The assembly of histones and DNA that is the basic
structural unit in chromatin nucleotide A phosphate ester of a nucleoside. A subunit of DNA or
RNA consisting of a nitrogenous base (adenine, guanine,
thymine, or cytosine in DNA; adenine, guanine, uracil, or
cytosine 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 RNA molecule. nucleotide diversity A measure of polymorphism applied to nucleic acid
sequences. The mean number of nucloetide differences per
site between any two randomly chosen sequences from a
population. nucleotide excision repair A repair process that corrects various types of DNA
damage by excising and resynthesizing a region of a
polynucleotide nucleotide substitution A mutation in which one nucleotide is substituted for
another. In evolution, the substitution of a nucleotide by
another nucleotide that becomes vixed in a population. nucleotypic Referring to a function of a DNA sequence other than as a
carrier of genetic information (e.g., serving as a skeleton
for the nucleus). nucleus The cellular organelle in a eukaryotic cell that contains
the chromosomes
