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TRANSCRIPTION

TRANSCRIPTION. DNA. Transcription. mRNA. Ribosome. Translation. Protein. DNA  RNA  Protein. Transcription. DNA is copied into messenger RNA (mRNA) by an enzyme called RNA polymerase in the nucleus mRNA is identical to DNA except Thymine (nucleotide) is replaced by Uracil

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TRANSCRIPTION

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Presentation Transcript

  1. TRANSCRIPTION

  2. DNA Transcription mRNA Ribosome Translation Protein DNA  RNA Protein

  3. Transcription • DNA is copied into messenger RNA (mRNA) by an enzyme called RNA polymerase in the nucleus • mRNA is identical to DNA except Thymine (nucleotide) is replaced by Uracil • mRNA is single stranded

  4. DNA vs. RNA

  5. When a cell needs a specific protein it sends a signal to the nucleus, telling it to make that protein • The nucleus makes a “photocopy” of the piece of DNA that carries the information for the desired protein: mRNA

  6. Transcription

  7. Steps of Transcription • Initiation • transcription machinery (made of RNA polymerases) is arranged on the template strand and binds to the promoter region

  8. a promoter • is a DNA sequence that tells the RNA polymerase • Where to start transcription • Which strand of DNA to transcribe • The direction to take from the start • every gene has a promoter, some are stronger than others

  9. 2. Elongation • RNA polymerase complex unwinds and opens a section of the double helix, about 10 bases at a time • transcription begins at the initiation site • RNA pol. adds bases at the 3’ end, elongating 5’  3’ • many mRNAs are made at once and the synthesis is fast: no proof-reading! • error rate 1/ 10^4

  10. 3. Termination • specific DNA sequences signal the end of transcription • RNA polymerase falls off, mRNA is free to leave

  11. http://bcs.whfreeman.com/thelifewire/content/chp12/1202001.htmlhttp://bcs.whfreeman.com/thelifewire/content/chp12/1202001.html

  12. Post-transcriptional modification • in prokaryotes mRNA can be used directly • often translation begins before the mRNA is completely transcribed! • in eukaryotes mRNA needs to be modified

  13. precursor mRNA mature mRNA • A 5’ guanine cap is added • A 3’ poly-A tail is added • Introns are spliced out - exons code

  14. pre-RNA molecule exon intron exon exon intron intron intron exon exon exon splicesome splicesome exon exon exon Mature RNA molecule RNA Processing

  15. enzymes that splice the pre-mRNA are called spliceosomes • alternative splicing allows for one gene to produce multiple proteins • guanine cap allows easy ribosome recognition • polyA tail allows the ribosome to stay on

  16. start codon A U G G G C U C C A U C G G C G C A U A A mRNA codon 1 codon 2 codon 3 codon 4 codon 5 codon 6 codon 7 stop codon protein methionine glycine serine isoleucine glycine alanine Primary structure of a protein aa2 aa3 aa4 aa5 aa6 aa1 peptide bonds Messenger RNA (mRNA)

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