RNAProtein160-page9 - The regions that do code for amino...

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Gene Expression – DNA to Protein - 9 Processing the mRNA Transcript Cap and Tail After transcription, the mRNA transcript has both a cap and a tail added. The cap is added to the 5' end of the RNA molecule (the end first synthesized) and a tail of adenine nucleotides is attached to the 3' end of the mRNA transcript. Both cap and tail help the mRNA attach to the ribosome for translation, and also inhibit enzyme degradation of the mRNA transcript. Introns and Exons The primary mRNA transcript in eukaryotes, when released from RNA polymerase, contains a mix of codable and non-coding RNA nucleotide sequences. The non- coding DNA segments are called introns (because they are intervening segments which interrupt the message) and do not code for amino acids.
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Unformatted text preview: The regions that do code for amino acids are called exons (because they are expressed). Prior to using a mRNA transcript the introns must be removed, which is done during the RNA processing stage. This process is called RNA splicing, because the introns are cut out and the remaining exons get spliced together. Special enzyme complexes are involved with the removal of introns. These complexes are called spliceosomes and are RNA-protein complexes. The removal of introns and splicing together of exons involves both protein enzymes and RNA catalysts. These RNA catalysts are called ribozymes, and are an important exception to the rule that all catalysts of living organisms are proteins....
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