BSC 197 Lecture Notes - Lecture 23: Frameshift Mutation, Silent Mutation, Release Factor

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Enzymes in the eukaryotic nucleus modify pre-mrna before the genetic messages are dispatched to the cytoplasm. During rna processing, both ends of the primary transcript are usually altered. Also, usually some interior parts of the molecule are cut out, and the other parts spliced together. Each end of a pre-mrna molecule is modi ed in a particular way: the 5 end receives a modi ed nucleotide 5 cap, the 3 end gets a poly-a tail. These modi cations share several functions: they seem to facilitate the export of mrna, they protect mrna from hydrolytic enzymes, they help ribosomes attach to the 5 end. Most eukaryotic genes and their rna transcripts have long noncoding stretches of nucleotides that lie between coding regions. These noncoding regions are called intervening sequences, or introns. The other regions are called exons because they are eventually expressed, usually translated into amino acid sequences.

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