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
