Genetics Chapter 14
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When can regulation of gene expression occur?
What are regulatory proteins?
proteins that bind to DNA and affect the rate of transcription of one or more nearby genes
What are the two types of regulatory proteins?
- repressors (inhibits)
- activators (increases)
What is a negative control regulatory protein?
What is a positive control regulatory protein?
- transcriptional regulation by repressors
- regulation by activators
What is an effector molecule?
- small molecule that doesn not bind directly to DNA, but rather to the regulatory protein causing confirmational changes in regulatory proteins
- regulatory protein can no longer bind to DNA, thus no regulation of transcription
How does the rate of transcription change when the effectory molecule binds to the regulatory protein?
- depends on what the regulatory protein is (if its a repressor or activator)
- regulatory proteins that respond to small effector molecules have two functional domains
What is a ligand?
- any molecule that binds to a specific site on a protein
- i.e. effector molecule
What is negative regulation?
bound receptor protein preents transcription
What is positive regulation?
bound activator protein promotes transription
What is an inducer?
small effector molecule that causes transcription to increase
What are the two possible ways to increase transcription (inducers)?
- A- bind to activator protein causing it to bind to DNA
- B- bind to a repressor protein preventing it from binding to DNA
What is a repressible gene?
the presence of a small effector molecule can inhibit transcription
What are the to possible repressible genes?
What is a corepressor? What is an inhibitor?
- small molecule tht binds to repressor protein causing the protein to bind to DNA
- small molecule that binds to activator protein preventing it from binding to the DNA
What are some examples of gene regulation in bacteria?
What is an operon?
a few structural genes arranged together in a regulatory unit under the transcriptional control of a single promoter
What is polycistronic mRNA?
transcribed from an operon; includes the transcript of two or more structural genes
What are some examples of regulation by negative control?
- default condition- operon off due to bound repressor
- repressor- 4 subunits each iwht an allolactose binding site
What is an allosteric enzyme?
- contians 2 binding sites
- effector binds to protein's allosteric site while the active site is bound to the DNA
What is an example of regulation by positive control?
- influenced by the presence of glucose (catabolite)
- allows bacterium to use diauxic growth (subsequential use of two sugars)
- in the presence of glucose and lactose, glucose is used up first
What is the CAP protein?
- catabolite activator protein
- two cAMP molecules funciton as allosteric effectors by increasing CAP affinity for DNA
- changes DNA confirmation in such a way that its going to want to bind to the NA site
CAP proteins allow _____ to bind and transcribe the genes involved in lactose _____.
What does CAP enhance?
the expression if the lac operon when lactose is present (glucose absent)
What does adenyl cyclase catalyze the formation of?
cAMP from ATP
When lactose is present and glucose is scarce _____ levels are high and _______ is synthesized.
What happens if the lac repressor binds to two of the three operator sites?
the resulting loop prevents RNA polymerase from recognizing the promoter site
What is the ara operon?
- another operon in E. coli involved in sugar metabolism
- regulated positively or negatively by the same regulatory protein
What happens in the absense of arabinose?
araC coded proteins bind to opeator sites, two of which interact to for a loop that inhibits BAD transcription
What happens in the presence of arabinose? (if glucose is not present, if glucose is present)
- the operon is activated?
- no glucose, cAMP allow CAP to bind promoting BAD transciption
- if glucose is present no cAMP and no binding of CAP and no promoting of BAD transcription
What are trpR repressor proteins? (with and without tryptophan)
- regulatory gene that produces the repressor
- with tryptophan- DNA can not transcribe
- without tryptophan- DNA can transcribe
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