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nuclear envelope:
Double membrane surrounding the nucleus. Consists of outer and
inner membranes perforated by nuclear pores.
nuclear lamina:
Fibrous layer on the inner surface of the inner nuclear membrane
made up of a network of intermediate filaments formed from nuclear
lamins.
nuclear magnetic resonance:
see NMR
nuclear pore:
Channel through the nuclear envelope that allows selected molecules
to move between the nucleus and cytoplasm.
nucleation:
Critical stage in the process of the assembly of a polymer at
which a small cluster of monomers aggregates in the correct
arrangement to initiate rapid polymerization; more generally,
the rate-limiting step in an assembly process.
nucleic acid:
RNA or DNA; consists of a chain of nucleotides joined together
by phosphodiester bonds.
nucleolar organizer:
Region of a chromosome containing a cluster of ribosomal RNA
genes that gives rise to a nucleolus.
nucleolus:
Structure in the nucleus where ribosomal RNA is transcribed
and ribosomal subunits are assembled.
nucleoside:
Compound composed of a purine or pyrimidine base linked to either
a ribose or a deoxyribose sugar.
nucleosome:
Structural, beadlike unit of a eucaryotic chromosome composed
of a short length of DNA wrapped around a core of histone proteins;
the fundamental subunit of chromatin.
nucleotide:
Nucleoside with one or more phosphate groups joined in ester
linkages to the sugar moiety. DNA and RNA are polymers of nucleotides.
nucleus:
Prominent membrane-bounded organelle in a eucaryotic cell, containing
DNA organized into chromosomes.
nurse cell:
Cell that is connected by cytoplasmic bridges to an oocyte and
thereby provides macromolecules to the growing oocyte.
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