01:119:115 Lecture Notes - Lecture 12: Rna Splicing, Transfer Rna, Genetic Code

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Eukaryotic cells modify rna after transcription: rna processing. Occurs before genetic messages are sent out of nucleus into cytoplasm. Both ends of primary transcript (pre-mrna molecule) are usually altered. Also, usually some interior parts of the molecule are cut out and other parts spliced together. Each end of a pre-mrna molecule is modified in a particular way fig 17. 10. The 5" end receives a modified nucleotide 5" cap (modified guanine) The 3" end gets a poly-a tail (50-250 adenine nucleotides) Functions of modification include: facilitating export of mrna from nucleus to cytoplasm, protect mrna from hydrolytic enzymes (enzymes that break stuff apart, help ribosomes attach to the 5" end. Rna splicing removes large non-coding portions of pre-mrna (portions that are not translated) fig 17. 11. The 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. Rna splicing removes introns and joins exons.

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