Ecclesiastes 3:1
description
Transcript of Ecclesiastes 3:1
©2000 Timothy G. Standish
Ecclesiastes 3:1
1 To every thing there is a season, and a time to every purpose under the heaven:
©2000 Timothy G. Standish
Transcription:Transcription:Concentrating on ProkaryotesConcentrating on Prokaryotes
Timothy G. Standish, Ph. D.
©2000 Timothy G. Standish
All Genes Can’t be Expressed All Genes Can’t be Expressed At The Same TimeAt The Same Time
Some gene products are needed by all cells all the time. These constitutive genes are expressed by all cells.
Other genes are only needed by certain cells or at specific times, expression of these inducible genes is tightly controlled in most cells.
For example, pancreatic cells make insulin by expressing the insulin gene. If neurons expressed insulin, problems would result.
©2000 Timothy G. Standish
Logical Expression Control PointsLogical Expression Control Points DNA packaging Transcription RNA processing mRNA Export mRNA masking/unmasking and/or
modification mRNA degradation Translation Protein modification Protein transport Protein degradation
Increasing costIncreasing cost
The logical place to control
expression is before the
gene is transcribed
The logical place to control
expression is before the
gene is transcribed
mRNA
Transcription
IntroductionIntroduction
The Central Dogma The Central Dogma of Molecular Biologyof Molecular Biology
Cell
Polypeptide(protein)
TranslationRibosome
Reverse transcription DNA
©2000 Timothy G. Standish
Stages of TranscriptionStages of Transcription Transcription can be logically divided
into four distinct stages:1. Template recognition2. Initiation3. Elongation4. Termination Each stage may participate in
regulation, but template recognition and termination appear to be major players
©2000 Timothy G. Standish
General Model For TranscriptionGeneral Model For Transcription
RNA Polymerase
Core Enzyme
Holoenzyme
©2000 Timothy G. Standish
General Model For TranscriptionGeneral Model For Transcription
©2000 Timothy G. Standish
General Model For TranscriptionGeneral Model For Transcription
©2000 Timothy G. Standish
General Model For TranscriptionGeneral Model For Transcription
©2000 Timothy G. Standish
NusA
General Model For TranscriptionGeneral Model For Transcription
Top-Isomerase
IGyrase
©2000 Timothy G. Standish
NusA
General Model For TranscriptionGeneral Model For Transcription
Top-Isomerase
IGyrase
Ribosome
Ribosome
Exo-nuclease
©2000 Timothy G. Standish
Ribosome
Ribosome
NusA
General Model For TranscriptionGeneral Model For Transcription
Exo-nuclease
©2000 Timothy G. Standish
Ribosome
NusA
General Model For TranscriptionGeneral Model For Transcription
Exo-nuclease
©2000 Timothy G. Standish
Ribosome
NusA
General Model For TranscriptionGeneral Model For Transcription
Exo-nuclease
©2000 Timothy G. Standish
NusA
General Model For TranscriptionGeneral Model For Transcription
Exo-nuclease
©2000 Timothy G. Standish
NusA
General Model For TranscriptionGeneral Model For Transcription
Exo-nuclease
©2000 Timothy G. Standish
NusA
General Model For TranscriptionGeneral Model For Transcription
Exo-nuclease
©2000 Timothy G. Standish
NusA
General Model For TranscriptionGeneral Model For Transcription
©2000 Timothy G. Standish
RNA PolymeraseRNA Polymerase RNA Polymerase is a spectacular
enzyme; it performs the following functions:
1. Recognition of the promoter region2. Melting of DNA (Helicase +
Topisomerase)3. RNA Priming (Primase)4. RNA Polymerization5. Recognition of terminator sequence
©2000 Timothy G. Standish
Prokaryotic Transcription InitiationProkaryotic Transcription Initiation The subunit of prokaryotic RNA
polymerase is necessary for promoter recognition and binding of RNA polymerase to the promotor
Different subunits allow recognition of different types of promoters; thus the type of genes transcribed can be modulated by altering the types of subunits which attach to RNA polymerase
©2000 Timothy G. Standish
Prokaryotic Transcription InitiationProkaryotic Transcription Initiation
Constitutive GeneHeat Shock GeneP1 P2
Different promoters
RNAPol.
©2000 Timothy G. Standish
Prokaryotic Transcription InitiationProkaryotic Transcription Initiation
Constitutive GeneHeat Shock Gene P2P1
Different promoters
RNAPol.
©2000 Timothy G. Standish
Transcription TerminationTranscription TerminationThere 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 with a hairpin and a U-rich region that destabilizes the elongation complex
©2000 Timothy G. Standish
RNAPol.
5’RNA
RNA Pol.
5’RNA
TerminationTerminationRho IndependentRho Independent
Terminator
©2000 Timothy G. Standish
RNAPol.
5’RNA RNA
Pol.
5’RNA
TerminationTerminationRho IndependentRho Independent
Terminator
©2000 Timothy G. Standish
RNAPol.
5’RNA
TerminationTerminationRho DependentRho Dependent
Terminator
RNA Pol.
5’RNA The terminator
sequence slows RNA polymerase
©2000 Timothy G. Standish
RNAPol.
5’RNA
TerminationTerminationRho DependentRho Dependent
Terminator
Help, Rhohit me!
RNA Pol.
5’RNA
Rho catches up with RNA polymerase
©2000 Timothy G. Standish
RNAPol.
5’RNA
TerminationTerminationRho DependentRho Dependent
Terminator
RNA Pol.
5’RNA
The elongation complex disintegrates
©2000 Timothy G. Standish
©2000 Timothy G. Standish
TranscriptionTranscription
5’
3’
3’
5’
Template (antisense) strand
Coding (sense) strand
©2000 Timothy G. Standish
TranscriptionTranscription
5’
3’
3’
5’
Template (antisense) strand
Coding (sense) strand
5’
RNA
RNAPol.
©2000 Timothy G. Standish
TranscriptionTranscription
5’
3’
3’
5’
5’
RNAPol.
Template (antisense) strand
Coding (sense) strand
©2000 Timothy G. Standish
Products of TranscriptionProducts of Transcription Transcription produces three major RNA products:
1 Ribosomal RNA (rRNA) - Several rRNAs are vital constituents of ribosomes
2 Transfer RNA (tRNA) - The molecule that physically couples nucleic acid codons with specific amino acids
3 Messenger RNA (mRNA) - The nucleic acid messenger that carries encoded information from genes on DNA to the protein manufacturing ribosomes
©2000 Timothy G. Standish
Transfer RNA (tRNA)Transfer RNA (tRNA) Acts as the adapter molecule between the genetic code
on mRNA and the protein “language” 75-85 bases long A specific amino acid is covalently linked at the 3’ end Elsewhere on the molecule is an anticodon
complimentary to the specific amino acid codon on mRNA that codes for the amino acid carried by the tRNA
Contain a number of modified bases
©2000 Timothy G. Standish
A “Simple” GeneA “Simple” Gene
Protein Coding Region
Terminator Sequence
Promoter/Control Region
Transcription Start Site 3’ Untranslated Region
5’ Untranslated Region
3’5’
RNA Transcript
©2000 Timothy G. Standish
Transcription InitiationTranscription InitiationProteins 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
©2000 Timothy G. Standish
RNA Pol.
InitiationInitiation
T. F.
RNA Pol.
5’RNA
Promoter
T. F.
T. F.
©2000 Timothy G. Standish
3’
5’
5’
3’
Transcription And Translation Transcription And Translation In ProkaryotesIn Prokaryotes
Ribosome
Ribosome5’
mRNA
RNAPol.
©2000 Timothy G. Standish
Heat Shock Response Heat Shock Response ElementsElements
Sudden changes in the temperature of cells cause stress in response to which heat shock genes are expressed
At least some heat shock genes are thought to be chaperones that help proteins fold correctly
Heat shock genes have Heat Shock Elements (HSEs) in their control regions
Heat Shock Transcription Factors (HSTFs) bind the HSEs up regulating expression of heat shock gene products
©2000 Timothy G. Standish
©2000 Timothy G. Standish
DNA
Cytoplasm
Nucleus
G AAAAAA
Export
Degradation etc.G AAAAAA
Control of Gene ExpressionControl of Gene Expression
G AAAAAA
RNAProcessing
mRNA
RNA
Transcription
Nuclear pores
Ribosom
e
Translation
Packaging
Modification
Transportation
Degradation
©2000 Timothy G. Standish
5’ 3’
RNA Transcript
A “Simple” GeneA “Simple” Gene
Protein Coding Region
Terminator Sequence
Promoter/Control Region
3’ Untranslated RegionTranscription Start Site 5’ Untranslated Region
©2000 Timothy G. Standish
RNA Pol.
InitiationInitiation
Promoter
RNA Pol.T. F.
T. F.
T. F.
5’RNA
©2000 Timothy G. Standish
3’
5’
5’
3’
Transcription And Translation Transcription And Translation In ProkaryotesIn Prokaryotes
Ribosome
Ribosome5’
mRNA
RNAPol.