9. Transcription Chapters 26 Lehninger 5 th Edition .
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Transcript of 9. Transcription Chapters 26 Lehninger 5 th Edition .
9. Transcription
Chapters 26 Lehninger 5th Edition
http://www.steve.gb.com/science/transcription.html
•Transcription•DNA -> RNA
•Translation•RNA -> Protein
Genes
• 1 gene -> 1 protein?
• Transcription– Read a gene from the DNA– DNA -> RNA
• Translation– Translate the DNA code to protein code– RNA -> Protein
Transcription
• RNA Polymerase– Reads DNA
• Makes RNA copy of– One strand
– One gene
Transcription
• Open DNA at promoter• Make RNA
– 5’-> 3’
– transcription bubble • Moves along gene
– Prevent DNA knotting• DNA topo-isomerases
Transcription
• Initiation– At promoters– Control by Transcription Factors– “Gene expression”
• Termination
• Processing of the transcript (Eukaryotes)– e.g. remove introns, add stuff to ends, modify bases
• Final product – e.g. mature mRNA or mature miRNA
Bacterial Promoters• Simple• Fixed spacing of binding sites• Transcription factors
Transcription Factors Bind DNA
Bacterial Gene Structure
• Simple promoter close to start of transcript• Gene transcribed as one piece of mRNA• Transcription terminates
– Terminator signal
• Ready to translate
m
Bacterial Operons• Genes may be grouped in Operons• Co-regulation• Single transcript
Eukaryotic Gene Structure
• V. complicated promoters– e.g. Human:
• 2000 TFs
• Spread over 10s of kb
• Several kb from coding region
• Pieces of mRNA removed before translation– Introns
• Rich Roberts, Phil Sharp
Eukaryotic gene processing
• Remove introns– Splicing
• Add 5’ cap• Cleavage of 3’ end of mRNA
at polyA site• Add 3’ polyA tail
Alternative transcripts
• Alternative polyA sites
• Alternative splicing– Alternative exons
• Alternative promoters
Alternative polyA
Alternative splicing
RNA Genome?
• Central dogma:– DNA -> RNA -> protein
• RNA Virus– e.g. HIV:
• RNA -> DNA
• Reverse transcriptase
What Controls Gene Expression?
• Transcription factors• Regulatory RNAs
– miRNA– smRNA– siRNA
• Methylation• Chromatin
Transcription Factors
• Proteins which bind DNA
• Enhance or repress gene expression– Families e.g.:
• Homeodomain (Hox)
• POU domain (Oct-1)
• Helix-loop-Helix (c-Myc)
• Zinc Fingers (TFIIIA)
• Leucine Zipper (c/EBP)
• Winged Helix (Fox family)
• Helix Turn Helix
• At least 10% of genes in Human genome are TFs