ap bio ch 18 pt 1
When CAP is activated, how does it affect the ability of RNA polymerase to bind to the promoter?
Active CAP helps RNA polymerase bind to the promoter
What is the inducer of the lac operon?
Allolactose
If lactose is present in an E. coli cell's environment, how does it affect the ability of RNA polymerase to transcribe the genes of the lac operon?
Allolactose will bind to the repressor. The repressor will become inactive and will not be bound to the operator, meaning RNA polymerase will be able to transcribe the genes of the operon.
What is an operon?
An operon is a cluster of functionally related genes that are controlled by a single promoter
What is repressible operon?
An operon that is on by default but can be turned off by a small molecule
What is an inducible operon?
An operon that is usually off, but can be induced to turn on by small molecules
How does binding of trp affect the repressor protein's shape and its ability to attach to the operator?
Binding of the corepressor to the repressor changes the conformation so the repressor can bind to the operator
What does the corepressor do?
Binds to the repressor and activates it. Typically the corepressor is the end product of a pathway.
What does the inducer do?
Binds to the repressor and turns it off. Typically the inducer is broken down.
What is the regulatory protein for the lac operon inducement process?
Catabolite activator protein (CAP)
What type of sugar is lactose?
Disaccharide
Do E. coli cells need trp all of the time or just occasionally?
E. coli needs tryptophan all of the time
What are the subunits of lactose?
Glucose and galactose
If glucose is NOT abundant, what is the concentration of cAMP?
High concentration
Why would not be advantageous for an E. coli cell to make the proteins to break down lactose if glucose was abundant in the environment?
If glucose is already abundant, the cell would not need to break down lactose to get more glucose.
Do E. coli cells need to constantly make their own trp?
If there is enough trp in the cell's environment, then the E. coli cell does not need to make more.
What is an isomer?
Isomers are molecules with the same molecular formula but with a different structure. Allolactose is an isomer of lactose.
Why does an E. coli cell need tryptophan?
It is one of the 20 amino acids needed to make proteins
How many genes to make the 3 enzymes needed for trp production?
It takes 5 genes to complete these 3 proteins.
How would an E. coli cell utilize lactose?
It will break down lactose down to its subunits. The glucose will be further broken down in order to produce ATP.
When the cell has enough trp, transcription of the genes is repressed. Why?
It would be a waste of energy and resources to make more trp
Do E. coli cells need to make enzymes all of the time?
It would only need to make the enzymes when lactose is abundant
Where do you find E. coli cells found in your body?
Large intestine/colon
Are inducible operons usually "on" or "off?"
Off
Are repressible operons usually "on" or "off?"
On
Do operons typically control one gene or multiple genes?
Operons control multiple genes
What is the role of the repressor?
Protein that binds to the operator and prevents RNA polymerase from transcribing the genes of the operon
Why do you think it is necessary for an organism to not actively transcribe all of their genes?
Proteins would be made when they aren't needed, which would be a waste of energy and resources.
When the repressor is attached to the operator, how does this affect the ability of RNA polymerase to transcribe the genes of the operon?
RNA polymerase is prevented from moving past the operator and transcribing the genes of the operon
What is the role of the promoter in an operon?
Region of DNA where RNA polymerase binds
What is the role of the operator in an operon?
Region of DNA where the active repressor binds
What is a corepressor?
The corepressor is the molecule that binds to the repressor of the repressible operon. This activates the repressor, allowing it to bind to the operator and prevent transcription.
What is the role of regulatory genes?
The gene that codes for the repressor protein
How does an inducer affect the repressor protein of an inducible operon?
The inducer binds to the repressor and this process inactivates the repressor. The inactive repressor cannot bind to the operator.
What is included in the operon?
The operator, promoter, and structural genes
What is the name of the gene that codes for the lac repressor protein?
lacI
What is NOT included in the operon?
The regulatory gene and the repressor
What is meant when the operon is considered "off?"
The repressor is active and genes are not being transcribed
If an E. coli cell has a surplus of trp, would the repressor be attached to the operator?
The repressor is attached to the operator
What is meant when the operon is considered "on?"
The repressor is inactive and genes are being transcribed
If there is no lactose present in an E. coli cell's environment, would the repressor protein be attached to the operator?
The repressor will be bound to the operator.
What are the names of the three genes in the lac operon?
lacZ, lacY, lacA
What are the two main ways of controlling metabolism in bacterial cells?
They use either feedback inhibition or adjust the production of the enzymes by regulating the expression of genes for the enzymes
How many enzymes does an E. coli need to make to produce trp?
Three enzymes
What do inducible operons do?
Typically break down substrates through catabolic processes
What do repressible operons do?
Typically build through anabolic processes
What is feedback inhibition?
When the product of a process can turn the process off when enough of it has been made
If lactose is present, will allolactose be present?
Yes, if lactose is present, allolactose will be present.
What is the role of cAMP?
cAMP activates CAP
What are the name of the five genes in the trp operon?
trpA, trpB, trpC, trpD, trpE
Which gene products are complete proteins?
trpC products
Which gene products join together to make complete proteins?
trpE + trpD products & trpB + trpA products
What is the name of the gene that codes for the trp repressor protein?
trpR
