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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;
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Transcription From DNA To RNA
Timothy G. Standish, Ph. D. Andrews University
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Introduction The Central Dogma of Molecular Biology
Cell DNA mRNA Transcription Polypeptide (protein) Translation Ribosome
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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
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A “Simple” Gene Transcription Start Site 3’ Untranslated Region
5’ 3’ Protein Coding Region Promoter/ Control Region RNA Transcript Terminator Sequence
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Stages of Transcription
Initiation Elongation Termination
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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
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Initiation T. F. Promoter RNA Pol. T. F. RNA Pol. T. F. 5’ RNA
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Initiation T. F. Promoter RNA Pol. T. F. T. F. RNA Pol. 5’ RNA
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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
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Termination Rho Independent
RNA Pol. 5’ Terminator RNA Pol. 5’
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Termination Rho Independent
RNA Pol. 5’ RNA Pol. 5’ Terminator
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Termination Rho Dependent
Terminator RNA Pol. 5’ r RNA Pol. 5’ r The terminator sequence slows RNA polymerase
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Termination Rho Dependent
Terminator RNA Pol. 5’ r Help, rho hit me! RNA Pol. 5’ r Rho catches up with RNA polymerase
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Termination Rho Dependent
Terminator RNA Pol. 5’ r r RNA Pol. 5’ The elongation complex disintegrates
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Differences Between Transcription In Prokaryotes and Eukaryotes
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Transcription And Translation In Prokaryotes
3’ 5’ 5’ mRNA RNA Pol. Ribosome Ribosome
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Eukaryotic Transcription
DNA Cytoplasm Nucleus Nuclear pores RNA Transcription G AAAAAA RNA Processing mRNA Export G AAAAAA
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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
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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
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The End
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