TOPIC 15 - TOPIC 15: TRANSCRIPTION pp. 665 - 681, 649 - 661...

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TOPIC 15: TRANSCRIPTION pp. 665 - 681, 649 - 661 Parts of the DNA sequence are coded into RNA. The RNA produced is complimentary to the DNA strand from which it is transcribed. Transcription involves the production of several different kinds of RNA (rRNA, tRNA and mRNA), each synthesized by a different RNA polymerase TRANSCRIPTION . This is the process by which the chemical information in DNA is copied into RNA (RNA or ribose nucleic acid). RNA differs from DNA in that RNA is single stranded (occasionally double stranded but this is internal double stranding.), contains the sugar ribose, uracil (U) substitutes for thymine, it readily breaks down, and exists in several forms. Copying the code from DNA occurs on the transcribed strand or 'template', leaving the opposing strand, the nontranscribed strand, idle. In transcription, the enzyme RNA polymerase binds to a DNA promoter region, the DNA double helix unwinds, and proceeding in the 5'-to-3' direction, RNA triphosphate nucleosides are paired to the exposed DNA bases. U instead of T is always paired with A. Transcription ends when RNA polymerase encounters a terminator (termination signal). Multiple transcription sites along a DNA strand are common. Note: the promoters and terminators are not the same as the 'start' and 'stop' codons you will see in translation. These consist of a 3 nucleotide base code whereas promoters and terminators consist of many more bases. Varieties of RNA. There are three kinds of RNA (1) rRNA or ribosomal RNA (2) mRNA or messenger RNA and (3) tRNA or transfer RNA. They must all undergo some modification between the time that they are transcribed into
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TOPIC 15 - TOPIC 15: TRANSCRIPTION pp. 665 - 681, 649 - 661...

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