18 Regulation of Gene Expression Flashcards
KEY CONCEPTS 18.1 Bacteria often respond to environmental change by regulating transcription 18.2 Eukaryotic gene expression is regulated at many stages 18.3 Noncoding RNAs play multiple roles in controlling gene expression 18.4 A program of differential gene expression leads to the different cell types in a multicellular organism 18.5 Cancer results from genetic changes that affect cell cycle control
What are some basic reasons that regulation of gene expression is important?
- Differentiation and Development of tissues
- Prevents enzyme being produced in the absence of substrate
- Organism won’t produce an amino acid if it already present readily
What are some basic reasons that regulation of gene expression is important?
- Differentiation and Development of tissues
- Prevents enzyme being produced in the absence of substrate
- Organism won’t produce an amino acid if it already present readily
What does ’biosynthesis’ refer to?
The producing of organic molecules by biological organisms
What is an example of a concept of gene expression regulation?
The operon
In what organisms are operons found?
Only bacteria
How do operons work?
They have an ‘operator’ in the promoter region which can selectively prevent the RNA polymerase from passing and thus prevents transcription.
The ‘operator’ prevents transcription only when it is bound to a ‘repressor’
Past the ‘operator’ are a group of genes which code for related functions.
This entire length of DNA consisting of the promotor (includes the ‘operator’) and the related genes is collectively called the ‘operon’
What is it called when multiple genes are simultaneously regulated?
Those genes are ‘coordinately controlled’
What does ’coordinately controlled’ refer to?
Gense whose expression is simultaneously regulated.
For example all the genes of the operon are co-ordinately controlled.
What does ’trp operon’ refer to?
A operon found in many bacteria which regulates the production of the amino acid ’tryptophan’
What does ’regulatory gene’ refer to?
A gene which codes for a protein which regulates gene expression
What is a gene which regulates the expression of others called.
A ‘regulatory gene’
What are the basic types of operons?
’Repressible operons’ and ‘inducible operons’
What are ‘repressible operons’ and how are they regulated?
In repressible operons the ‘repressor’ is transcribed form the ‘regulatory gene’ in its inactive form. Therefore the ‘operator’ region remains unbound and thus transcription occurs unimpeded.
If a ‘corepressor’ is present it binds to the ‘repressor’ aden thus activates it. This allows the repressor to binds to the operator region and thus transcription is halted.
Eventually the active repressor degrades. Therefore if the corepressor is removed the newly formed repressors will not be activated and thus transcription will resume
What class of proteins are the repressors of operons?
‘Allosteric proteins‘
What are ‘inducible operons’ and how are they regulated.
The ‘repressor’ is transcribed from the ‘regulatory gene’ in its active form.
Therefore only when an ‘inducer’ binds to the repressor and inactivates is the operator cleared and thus transcription of the operon allowed to continue
What does ’inducer’ refer to?
A substance which binds to the repressor to inactivate it.
Therefore their presence allows the transcription of the genes of a inducible operon.
What does ’co-repressor’ refer to?
A substance which binds to a repressor and thus activates it.
This allows the repressor to bind to the operator and thus transcription is prevented in ‘repressible operons’
What are the factors which allosterically prevent transcription of operons called?
‘Corepressors’
What are the factors which allosterically stimulate transcription of operons called?
‘Inducers’
What are ‘repressible operons’ typically involved in?
Anabolic pathways i.e. biosynthesis.
This is because they can prevent wasting resources on building substances which are already abundant if those end products act as ‘corepressor’
What are ‘inducible operons’ typically involved in?
Catabolic pathways i.e. the breakdown of substrates.
This is because only when the substate is present will it stimulate the transcription of genes to break it down.
What is a further method of regulating operons?
The use of ‘activators’
How do activators stimulate transcription?
When activated they bind to the DNA in the promoter region. This increases the affinity of the DNA to the RNA polymerase. This encourages it to bind more regularly and thus transcription rate increases
What is the use of activators in the regulation of gene expression called?
‘Positive gene control’
What does ’positive gene control’ refer to?
The use of ‘activators’ to affect gene expression
What does ’activators’ refer to?
Substances which affect gene expression through ‘positive gene expression’
What is a specify example of an operon?
The ‘lac operon’
What is the lac operon control?
An inducible operon which causes the release of enzymes involved in the metabolism of lactose.
The inducer it uses is ‘allolactose’ which is an alternative form of lactose.
If the glucose levels in the cell are low, cAMP is produced. This activates a catabolite activator protein (CAP) which binds to the promoter region and thus increases the rate of transcription.
This form of ‘positive gene control’ is important as it ensures that the enzymes to break down lactose are not produced if both glucose and lactose are present.
If no ‘activator’ binds to the promoter region during ‘positive gene control’, can transcription still occur?
Yes albeit at a slower rate.
What is an analogy for the repressor/inducer’s affects on an operon versus an activator during positive gene control?
The repressors are like on-off switches which turn the operon on or off i.e transcription either occurs or doesn’t
Transcription can occur even if the activator is not present. Therefore ‘positive gene control’ is more like a volume switch of transcription.
What does ’biosynthesis’ refer to?
The producing of organic molecules by biological organisms
What is an example of a concept of gene expression regulation?
The operon
In what organisms are operons found?
Only bacteria
How do operons work?
They have an ‘operator’ in the promoter region which can selectively prevent the RNA polymerase from passing and thus prevents transcription.
The ‘operator’ prevents transcription only when it is bound to a ‘repressor’
Past the ‘operator’ are a group of genes which code for related functions.
This entire length of DNA consisting of the promotor (includes the ‘operator’) and the related genes is collectively called the ‘operon’
What is it called when multiple genes are simultaneously regulated?
Those genes are ‘coordinately controlled’
What does ’coordinately controlled’ refer to?
Gense whose expression is simultaneously regulated.
For example all the genes of the operon are co-ordinately controlled.
What does ’trp operon’ refer to?
A operon found in many bacteria which regulates the production of the amino acid ’tryptophan’
What does ’regulatory gene’ refer to?
A gene which codes for a protein which regulates gene expression
What is a gene which regulates the expression of others called.
A ‘regulatory gene’
What are the basic types of operons?
’Repressible operons’ and ‘inducible operons’
What are ‘repressible operons’ and how are they regulated?
In repressible operons the ‘repressor’ is transcribed form the ‘regulatory gene’ in its inactive form. Therefore the ‘operator’ region remains unbound and thus transcription occurs unimpeded.
If a ‘corepressor’ is present it binds to the ‘repressor’ aden thus activates it. This allows the repressor to binds to the operator region and thus transcription is halted.
Eventually the active repressor degrades. Therefore if the corepressor is removed the newly formed repressors will not be activated and thus transcription will resume
What class of proteins are the repressors of operons?
‘Allosteric proteins‘
What are ‘inducible operons’ and how are they regulated.
The ‘repressor’ is transcribed from the ‘regulatory gene’ in its active form.
Therefore only when an ‘inducer’ binds to the repressor and inactivates is the operator cleared and thus transcription of the operon allowed to continue
What does ’inducer’ refer to?
A substance which binds to the repressor to inactivate it.
Therefore their presence allows the transcription of the genes of a inducible operon.
What does ’co-repressor’ refer to?
A substance which binds to a repressor and thus activates it.
This allows the repressor to bind to the operator and thus transcription is prevented in ‘repressible operons’
What are the factors which allosterically prevent transcription of operons called?
‘Corepressors’
What are the factors which allosterically stimulate transcription of operons called?
‘Inducers’
What are ‘repressible operons’ typically involved in?
Anabolic pathways i.e. biosynthesis.
This is because they can prevent wasting resources on building substances which are already abundant if those end products act as ‘corepressor’
What are ‘inducible operons’ typically involved in?
Catabolic pathways i.e. the breakdown of substrates.
This is because only when the substate is present will it stimulate the transcription of genes to break it down.
What is a further method of regulating operons?
The use of ‘activators’
How do activators stimulate transcription?
When activated they bind to the DNA in the promoter region. This increases the affinity of the DNA to the RNA polymerase. This encourages it to bind more regularly and thus transcription rate increases
What is the use of activators in the regulation of gene expression called?
‘Positive gene control’
What does ’positive gene control’ refer to?
The use of ‘activators’ to affect gene expression
What does ’activators’ refer to?
Substances which affect gene expression through ‘positive gene expression’
What is a specify example of an operon?
The ‘lac operon’
What is the lac operon control?
An inducible operon which causes the release of enzymes involved in the metabolism of lactose.
The inducer it uses is ‘allolactose’ which is an alternative form of lactose.
If the glucose levels in the cell are low, cAMP is produced. This activates a catabolite activator protein (CAP) which binds to the promoter region and thus increases the rate of transcription.
This form of ‘positive gene control’ is important as it ensures that the enzymes to break down lactose are not produced if both glucose and lactose are present.
If no ‘activator’ binds to the promoter region during ‘positive gene control’, can transcription still occur?
Yes albeit at a slower rate.
What is an analogy for the repressor/inducer’s affects on an operon versus an activator during positive gene control?
The repressors are like on-off switches which turn the operon on or off i.e transcription either occurs or doesn’t
Transcription can occur even if the activator is not present. Therefore ‘positive gene control’ is more like a volume switch of transcription.
What are the fundamental ways proteins are modified?
Cleaved, chemical modification i.e the addition of carbohydrates.
What are the basic ways in which gene expression in Eukaryotes is regulated?
Regulation of the chromatin structure, regulation of Transcription Initiation and methods of Post-Transcriptional regulation.
What are the basic ways the regulation of chromatin structure affects DNA expression?
Histone modification, DNA Methylation and Epigenetic inheritance.
Besides affecting histone tails, how does acetylation affect gene expression?
Some enzymes that acetylate or deacetylate histones are closely associated with or even components of the transcription factors that bind to promoters.
This suggest that histone acetylation enzymes also promote transcription by binding to and thus “recruiting” components of the transcription machinery.
What are the basic stages of gene expression in eukaryote?
Chromatin Modification forms transcriptable DNA, then:
Transcription → RNA processing → Transport to Cytoplasm → Translation → Protein Processing → Transport to cellular destination.
Where does Transcription occur in Eukaryotes?
Nucleus
Where does RNA Processing occur in Eukaryotes?
Nucleus
Where does Translation occur in Eukaryotes?
Cytoplasm (free ribosomes) or on E.R. (bound ribosomes)
What are the fundamental ways proteins are modified?
Cleaved, chemical modification i.e the addition of carbohydrates.
Why is the regulation gene expression particularly important in multicellular organisms?
It allows “differential gene expression” where the gene dosage can be adjusted to lead to specialised cells or for temporal fluctuations i.e. puberty.
What is it called when the rates of gene expression varies between cells?
“Differential gene expression”
What does ’differential gene expression’ refer to?
The expression of different genes by cells with the same genome.
What are the basic ways in which gene expression in Eukaryotes is regulated?
Regulation of the chromatin structure, regulation of Transcription Initiation and methods of Post-Transcriptional regulation.
What are the purposes of DNA packing?
It ensures the DNA fits in the nucleus and helps alter gene expression
What are the basic ways the regulation of chromatin structure affects DNA expression?
Histone modification, DNA Methylation and Epigenetic inheritance.
What are the basic ways in which histone modification can lead to the regulation of gene expression?
‘Histone acetylation’, ‘histone methylation’ and the phosphorylation.
