Genetics #3 Flashcards
Why regulate genetics?
- Saves materials
2. Saves energy
What are 2 ways gene expression is regulated?
- Transcriptional Initiation
2. Translation
Regulates activity of enzymes and proteins between active and inactive forms
Post Translational Regulation
What are the 3 primary ways Bacteria and Archaea regulate transcription?
- Constituive Gene Regulation
- Inducible Gene
- Repressible Gene
Gene regulation that… uses housekeeping genes that are transcribed all the time at low levels to replace old proteins that are at the end of their life
Constitutive Genes Regulation
- Genes that are expressed (transcribed) only when certain specific substances (inducers) are present in the environment
- Most commonly involved in catabolism
Inducible Genes
Genes that are normally expressed but repressed (shut down gene expression) when certain substances (corepressors) are present in the environment
-Most common in biosynthesis
Repressible Genes
For a gene to be transcribed, the promoter of that gene must be… (2)
- Accessible to the RNA polymerase
2. The RNA polymerase must then bind to the promoter
To regulate transcription of a gene, a cell can control… (2)
- Access to the promoter
2. How well the RNA polymerase can bind
If there is not access to the promoter… transcription (can/cannot) occur
Cannot
How do prokaryotes block access to the promoter?
-When a special allosteric protein (repressor protein) binds to a segment of DNA called the operator in front of the gene
How do Eukaryotes block access to the promoter?
Controlled by the degree of chromatin condensation
If chromatin is tightly condensed…
Access is blocked and there is no transcription
When chromatin is more loosely condensed…
Access is open and transcription can occur
The process of opening or tightening the chromatin to allow/ prevent transcription
Chromatin Modeling
How is chromatin modeling controlled?
Histone and non histone proteins
How do prokaryotes regulate binding strength of RNA polymerase to the promoter and SLOW transcription?
-If the repressor is not bound to the operator, only a low level of transcription can occur (constitutive synthesis)
How do prokaryotes regulate binding strength of RNA polymerase to the promoter and INCREASE transcription?
-For higher levels of transcription, other proteins must first bind to the promoter (activator proteins)- these promote the binding of RNA polymerase more strongly and result in a higher level of transcription
How do Eukaryotes regulate binding strength of RNA polymerase to the promoter?
-If the chromatin is relaxed, the access to the promoter is open
RNA polymerase will only bind to the promoter with the help of proteins called…
Transcription Factors
-Binding of regulatory repressor protein at DNA regulatory site (operator) inhibits the initiation of transcription
Negative Transcriptional Control
- Proteins that exist in active or inactive forms
- Inducers and compressors alter the activity of the repressor by binding
Repressor Proteins
Type of reaction that we WANT so we add an…
Add a inducer, and it is an INDUCIBLE reaction
Type of reaction that we don’t want, so we add…
Add a corepressor, and it is an REPRESSIBLE reaction
If the whole reaction is an inducer, we add a repressor and it… (stops/starts)
Stops
If the whole reaction is a repressor, we add an inducer and it… (stops/starts)
Starts
Binding of activator protein at a regulatory region on DNA promotes transcription initiation
Positive Transcriptional Control
In positive transcriptional control, mRNA synthesis is… (increased/decreased)
Increased
How is activation turned on or off in Positive Transcriptional Control? (3)
- Inactive protein is activated by an inducer
2. Active protein is inactivated by an inhibitor
Inducable Genes b-Gal Enzyme
- Inducible enzyme functions in a catabolic pathway
- Inducable genes are present only when their substrate(inducer/ effector molecule) is present
b-Gal reaction catalyzed is lactose hydrolysis into…
- Galactose
2. Glucose
Enzyme that function in biosynthetic pathways are products of…
Repressor Genes
Enzymes for repressor genes are always present unless the end product of the biosynthetic pathway is (available/not available)
Available
Promoter and operator, or activator binding sites, along with functionally related structural genes
-They are grouped together in the DNA
Operon
In Bacteria and Archaea (monocistronic/polycistronic) mRNA is produced?
Polycistronic mRNA
Type of Protein that controls the gene expression for all the genes?
Regulatory Proteins
Lactose (Lac) Operon overview
Coding for lactose metabolism or uptake
When the lac repressor binds to the operator…
Inhibits transcription by blocking access to the promoter for genes
Enzymes for Lac Operon aren’t normally produced unless _____ is present
Lactose
The repressor protein always binds to the…
Operator
- Allosteric enzyme that exists in binding form and non binding form
- Bend DNA and prevent RNA polymerase from accessing promoter
- Presence of allolactose (inducer) binds receptor
Lac Repressor
Consists of 5 structural genes with code for enzymes needed to synthesize tryptophan
-Negative transcriptional control of repressible genes by trp repressor indicates that…
The operon functions only in the absence of tryptophan
Regulation of Gene Expression is Eukarya and Archaea
Chromatin Remodeling
Lossening of chromatin to allow RNA polymerase access to the promoter
Chromatin Remodeling
How is chromatin remodeling regulated?
By histone and non histone proteins
How do Eukaryotes control gene expression?
Using regulatory transcription factors to regulate transcription initiation
When activators bind enhancers…
mRNA transcription increases
When repressor proteins bind silencers…
mRNA transcription decreases
