Microbial Genetics III Translation and Gene Regulation PDF

Translation and Gene Regulation Structure of a Gene and mRNA  The Unit of Transcription Prokaryotes –The unit of transcription often contains more than a single gene. – One mRNA may contain info for information for more than one polypeptide –Genes of rel...

Translation and Gene Regulation Structure of a Gene and mRNA  The Unit of Transcription Prokaryotes –The unit of transcription often contains more than a single gene. – One mRNA may contain info for information for more than one polypeptide –Genes of related pathways often clustered together –All genes in a pathway may be cotranscribed Polycistronic mRNA  Eukaryotic Transcription Three different types of RNA Polymerases – RNA Polymerase I – most rRNAs – RNA Polymerase II – most mRNAs – RNA Polymerase III – tRNAs some rRNAs Do not use Sigma Factors Use Transcription Factors – Proteins bind to Specific DNA sequences Eukaryotic RNA Polymerase RNA processing in Eukaryotes Figure 8.11  Ask your neighbor to: Describe DNA transcription. – What initiates? – What enzyme? – Which direction? – What is a promoter? – How do prokaryotes compare to eukaryotes  Transcription Termination Terminators stop RNA polymerase Two Main Types –Sequence determined Intrinsic terminators Inverted repeats –Rho dependent Rho binding sequence Rho protein binds RNA  Rho termination Rho RNA helicase Binds to specific “Rut” site upstream of promoter Moves along RNA until “traps” RNA Polymerase  Rho termination J. Mol. Biol. (2012) 423, 664–676  Transcription What is it for? What does the transcribing? What initiates and where? What terminates? Where does this occur in Eukaryotes and Prokaryotes?  Messengers carry the message RNA after the introns are spliced out is known as: mRNA or Messenger RNA  Genetic Code The genetic code is expressed in terms of RNA Codon = 3 letter word for each amino acid A single amino acid may be encoded by several different but related codons.  DNA stores a coded language Language is spelled out in linear form Only has 4 characters(G, C, A, T) Each “word” only 3 letters long! The Genetic Code 5’ CGA AAC GCU AUA AGU GAA GCC UCC UAU 3’ Translation Figure 8.9, step 1 Translation Figure 8.9, step 3 Gene Regulation levels  Transcriptional Translational Post Translational Constitutive  Transcriptional Control Often involves DNA binding proteins Recognize specific sequences of DNA Two main types of Control – Negative – decreasing level of mRNA – Binding of repressor to an operator sequence Repression – corepressor protein Induction - inducer – Positive – Increasing level of mRNA – Binding of activator to activator binding site Activator – DNA binding protein  Two types of pathways Inducible – Usually turned off – Presences of substrate turn it on Repressible – Usually turned on – Presence of product turns it off  Bacterial Regulatory Proteins Allosteric DNA Binding Proteins – Bind DNA – Bind effector molecule Effector influences binding to DNA – Inducer – prevents repressor from binding – Corepressor – activates repressor allows binding Figure 12.5 Next Time, Examples of Gene Regulation in Prokaryotes Operons