Chapter 13 Transcription

RNA in the Primeval World What came first proteins or nucleic acids? or chicken Or the……… EGG! Life’s Paradox…

1981: Tomas Cech Discovered: n RNA could act as enzymes=Ribozymes! Ribozyme RNA Tetrahymena thermophila

RNA structure Reminder of RNA structure. What are differences between DNA and RNA? Review Question:

RNAs Functional transfer RNAs Vital for protein translation ribosomal RNAs Forms complexes with proteins Vital for protein translation Informational messenger RNAs Intermediates in decoding genes into proteins And now many more! TRADITIONAL CLASSIFICATION of RNAs

Additional functional classes of RNA n Small nuclear RNAs n Small nucleolar RNAs n Small cytoplasmic RNAs n Small Interfering RNAs n MicroRNA n  n  n  n  n  Molecule of the year 2002

RNA Transcription  ’  ’ 

The Basic Model Let’s look closely at the process of transcription. terminator

Transcription unit with more detail

Four key components of transcription n Promoter n Transcription start site n RNA coding region n The Terminator

Process of Bacterial Transcription n Initiation n Elongation n Termination

Prokaryotic Initiation

 Prokaryotic: RNA Polymerase Required for Initiation of Transcription Can only continue transcription ωω

RNA polymerase binds

Prokaryotic Elongation

The Search The Binding: “Closed Complex” The Unwinding: “Open complex” Transcription Begins: Sigma factor leaves RNA Polymerase ω

Transcription is always 5’ to 3’

Prokaryotic Termination

Transcription Termination n 2 mechanisms q rho dependent q rho independent

Rho Dependent Binding of rho protein Secondary RNA structure Rho protein has helicase activiity!

Rho Independent Speed bump

Eukaryotic Transcription

Eukaryotic Initiation

Promoter of RNA polymerase II Affects rate of transcription

Promoter recognition and transcription initiation ■BASAL TRANSCRIPTION APPARATUS □General Transcription Factors □RNA Polymerase □Mediator proteins ■Transcriptional Activator Proteins

General Transcription Factors (for example: for RNA Polymerase II) 1. TFIIA 2. TFIIB 3. TFIID 4. TFIIE 5. TFIIF 6. TFIIH

Binds to minor groove

Eukaryotic Transcriptional Termination n Protein dependent termination q But proteins binds DNA not RNA n Protein Independent q but no hairpin loop

n Eukaryotes n Arachae n Eubacteria Evolution and Regulatory Sequences TATA BINDING PROTEINS NO TATA BINDING PROTEINS