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- Nasal Polyp: A small, pearly-gray, stalk-like growth from the epithelial surface inside the nose.
- Nasal Potential Difference: A method for measuring channel function in the nasal epithelium that has been used as a diagnostic technique for cystic fibrosis.
- Nonsenses Mutation: A change in one DNA base pair. Instead of substituting one amino acid for another, however, the altered DNA sequence prematurely signals the cell to stop building a protein (i.e. a stop codon). This type of mutation results in a shortened protein that may function improperly or not at all.
- Nucleotide: A molecule consisting of a nitrogenous base (adenine, guanine, thymine, or cytosine in DNA; adenine, guanine, uracil, or cytosine in RNA), a phosphate group, and a sugar (deoxyribose in DNA; ribose in RNA). DNA and RNA are polymers of many nucleotides.
- Nucleus: A central structure in the cell that contains genetic material (DNA) and controls cellular function and division.