Hebrews 1 1 God, who at sundry times and in divers manners spake in time past unto the fathers by the prophets, 2 Hath in these last days spoken unto us by his Son, whom he hath appointed heir of all things, by whom also he made the worlds;

Transcription From DNA To RNA Timothy G. Standish, Ph. D. Andrews University

Introduction The Central Dogma of Molecular Biology Cell DNA mRNA Transcription Polypeptide (protein) Translation Ribosome

RNA Polymerase RNA Polymerase is a spectacular enzyme, functioning in: Recognition of the promoter region Melting of DNA (Helicase + Topisomerase) RNA Priming (Primase) RNA Polymerization Recognition of terminator sequence

A “Simple” Gene Transcription Start Site 3’ Untranslated Region 5’ 3’ Protein Coding Region Promoter/ Control Region RNA Transcript Terminator Sequence

Stages of Transcription Initiation Elongation Termination

Transcription Initiation Proteins called transcription factors bind to the promoter region of a gene If the appropriate transcription factors are present, RNA polymerase binds to form an initiation complex RNA polymerase melts the DNA at the transcription start site Polymerization of RNA begins

Initiation T. F. Promoter RNA Pol. T. F. RNA Pol. T. F. 5’ RNA

Initiation T. F. Promoter RNA Pol. T. F. T. F. RNA Pol. 5’ RNA

Transcription Termination There are two types of termination: Rho dependent requires a protein called Rho, that binds to and slides along the RNA transcript. The terminator sequence slows down the elongation complex, Rho catches up and knocks it off the DNA Rho independent termination depends on both slowing down the elongation complex, and an AT rich region that destabilizes the elongation complex

Termination Rho Independent RNA Pol. 5’ Terminator RNA Pol. 5’

Termination Rho Independent RNA Pol. 5’ RNA Pol. 5’ Terminator

Termination Rho Dependent Terminator RNA Pol. 5’ r RNA Pol. 5’ r The terminator sequence slows RNA polymerase

Termination Rho Dependent Terminator RNA Pol. 5’ r Help, rho hit me! RNA Pol. 5’ r Rho catches up with RNA polymerase

Termination Rho Dependent Terminator RNA Pol. 5’ r r RNA Pol. 5’ The elongation complex disintegrates

Differences Between Transcription In Prokaryotes and Eukaryotes

Transcription And Translation In Prokaryotes 3’ 5’ 5’ mRNA RNA Pol. Ribosome Ribosome

Eukaryotic Transcription DNA Cytoplasm Nucleus Nuclear pores RNA Transcription G AAAAAA RNA Processing mRNA Export G AAAAAA

A “Simple” Eukaryotic Gene Transcription Start Site 5’ Untranslated Region 3’ Untranslated Region Introns 3’ 5’ Exon 2 Exon 3 Int. 2 Exon 1 Int. 1 Promoter/ Control Region Exons Terminator Sequence RNA Transcript 3’ 5’ Exon 2 Exon 3 Exon 1 Int. 2 Int. 1

Processing Eukaryotic mRNA 3’ Untranslated Region 5’ Untranslated Region Protein Coding Region 5’ G 5’ Cap 3’ 5’ Exon 2 Exon 3 Int. 2 Exon 1 Int. 1 3’ AAAAA 3’ Poly A Tail Exon 2 Exon 3 Exon 1 Int. 2 Int. 1 RNA processing achieves three things: Removal of introns Addition of a 5’ cap Addition of a 3’ tail This signals the mRNA is ready to move out of the nucleus and may control its life span in the cytoplasm

The End