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description: composed of a five carbon sugar that is attached to one or more phosphate group and a nitrogen containing base.

In DNA the sugar is deoxyribose attcahed to a single phosphate group. The base is either adenine, cytosine, guanine, or thymine

Nuclear lamina

def: a network of protein filaments that form a thin layer underlying and the inner nuclear membrane

Nucleolus (chapter 5)

def: where parts of the different chromosomes carrying genes for the ribosomal RNA's are sythesized and combined with proteins to form ribosomes.

Nucleosome (chapter 5)

def: Beadlike structural unit of a eukaryotic chromosome composed of a short length of DNA wrapped around a core of histone proteins; the fundamental subunit of a chromatin.

Nonhomologous End-Joining (chapter 6)

def: Mechanism for repairing double-strand breaks in DNA in which the two broken ends are brought together and rejoined without requiring sequence homology.

Nuclear Envelope (chapter 15)

def: Double membrane surrounding the nucleus. Consists of outer and inner membranes perforated by nuclear pores.

Nuclear Pore (chapter 15)

def: Channel through the nuclear envelope that allows selected large molecules to move between the nucleus and the cytoplasm.

Neurotransmitter (chapter 16)

def: Small signaling molecule secreted by a nerve cell at a chemical synapse to signal to the post synaptic cell. Examples include acytlcholine, glutamate, GABA, and glycine.

Nitric Oxide (NO) (chapter 16)

def: Small, highly diffusible molecule widely used as an intracellular signal.

Nuclear Receptor (chapter 16)

def: Receptor proteins present inside a eukaryotic cell that can bind to signal molecules that enter the cell such as steroid hormones; the complex of nuclear receptor and signal molecule; subsequently acts as a transcription regulator.

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