Chapter 6: 6.7 Introduction to Regulation of Gene Expression Flashcards
Why are not all genes expressed at the same time?
Organisms regulate gene expression in order to:
* Conserve energy and resources when certain gene products are not required
What levels can gene expression be regulated?
- Epigenetic
- Transcriptional
- Post-Transcriptional
- Translational
- Post-Translational
What do epigenetic and transcriptional regulation involve?
Whether a gene (DNA) gets to be transcribed into RNA
List:
Examples of epigenetic and transcriptional regulation
- Whether the gene is physically accessible (epigenetic)
- Presence of special molecules called transcription factors to recruit RNA polymerase (transcriptional)
- RNA splicing and control of RNA stability (transcriptional)
What does translational regulation involve?
Involves controlling mRNA translation into proteins
What does post-translational regulation involve?
Involves modification of the expressed protein, modulating its activity
Define:
Constitutively expressed genes
Genes that are expressed continuously
True or False:
Constitutively expressed genes are not regulated
False
How can expression levels of constitutively expressed genes be regulated?
- Promoter strength (transcriptional regulation)
- mRNA half-life (translational regulation)
How is a promoter determined to be “stronger”?
Has a sequence closest to the consensus sequence
* Bounds more often and more strongly by RNA polymerase
* Leads to more transcripts
True or False:
Only eukaryotes can have all 3 levels of gene regulation
False, eukaryotes and prokaryotes can both have all 3 levels of gene regulation
Unlike eukaryotes, bacteria can have - ——- —- between a promoter and a terminator or ——– —– – ——
- A single gene
- Multiple genes in tandem
What is an operon?
In prokaryotes, multiple genes in tandem
Describe:
Single Protein Genes in Prokaryotes
- One promoter, coding region and terminator
- Encodes for one protein
(2 points)
Describe:
Operons (Multi-Protein Gene) in Prokaryotes
(3 points)
- One promoter, several protein coding regions, on terminator
- Encodes for multiple proteins
- Several start and stop codons to define the beginning/end of each protein
Where is an operator located?
Directly upstream or downstream of the promoter
- What binds to the operator?
- What does it do?
- Regulatory proteins
- Controls when RNA polymerase binds to promoter to activate transcription
What is responsible for transcriptional regulation?
Operator and Regulatory Proteins
What is translational regulation?
Means affecting mRNA before it gets translated into proteins
What are some methods of translational regulation?
- mRNA is degraded before it gets translated
- mRNA have short RNAs bind to prevent ribosome from binding
When does post-translation regulation occur?
Occurs after translation of mRNA into proteins
What are some methods of post-translational regulation?
- Degradation of produced proteins to directly control their levels in the cell
What is a degron?
A sequence on the protein that designates it for degradation
How does degradation of produced proteins in post-translation regulation work?
- Recognin binds to the degron sequence of a protein
- Brings protein to a proteosome
What is a proteosome?
A group of proteins that degrade other proteins
Why can transcription and translation occur simultaneously in prokaryotes?
They do not have a separate compartment for the nucleus
What are the regulatory proteins that control gene expression in many common prokaryotic systems called?
Activators and Repressors
What is the basic structure of a regulatory protein?
(3 points)
- Contains a DNA binding region
- Binds to the operator next to the promoter
- Can also have a allosteric site that controls the DNA binding site
True or False:
Some regulatory proteins have an allosteric site that is controlled by the DNA binding site
False, the allosteric site CONTROLS the DNA binding site
Define:
Activators
Promotes binding of RNA polymerase to the promoter to activate transcription
* Involved in positive regulation
Define:
Repressors
Prevents RNA polymerase from binding to the promoter to inhibit transcription
* Involved in negative regulation
What can activators and repressors be influenced by?
Small molecules:
* Inducers
* Inhibitors
* Co-repressors
Define:
Inducers
Promote gene expression by inactivating repressors or activating activators
Define:
Inhibitors
Prevent gene expression by inhibiting activators
Define:
Co-repressors
Prevent gene expression by activators repressors
True or False:
Activators are involved in negative regulation
False, they are involved in positive regulation
True or False:
Repressors are involved in positive regulation
False, they are involved in negative regulation
How do inducers promote gene expression?
By inactivating repressors OR activating activators
How do inhibitors prevent gene expression?
By inhibiting activators
How do co-repressors prevent gene expression?
By activating repressors
Describe:
Positive regulation
Activators may be always bound to DNA promoting transcription
* In other cases, activators are not bound and they require an inducer to bind to DNA
Describe:
Negative regulation
Repressors may be always bound to DNA inhibiting transcription
* In other cases, repressors are not bound and they require a co-repressor to bind
What would be required to stop positive regulation?
An inhibitor
What would be required to stop negative regulation?
An inducer
