Lecture 8 - Catabolite Repression and Transcriptional Termination Flashcards
What happens with the activity of enzymes for lactose metabolism when you add lactose to the medium?
The activity of the enzymes increases
What happens to the synthesis of lactose when glucose is added to the medium and why?
The synthesis of lactose goes down when glucose is added because glucose turns off the operon
What happens to the activity of enzymes when they are involved in the activity of any sugar?
The activity of enzymes increases when involved in metabolism of any sugar
What represses the metabolism of sugar?
The addition of glucose to the medium represses the activity of enzymes involved in the metabolism of any sugar.
What is the growth rate of E. coli on various carbon sources (glucose, lactose, arabinose and glycerol)?
- Glucose: growth rate = 30 minutes
- Lactose: growth rate = 50 minutes
- Arabinose: growth rate = 55 minutes
- Glycerol: growth rate = 70 minutes
`What are you able to determine by looking at the growth rates of E. coli with various carbon sources (glucose, lactose, arabinose and glycerol) ?
- able to determine how much sugar is derived from each of these sources
Is more energy extracted from glucose than lactose?
- No, but yes for the net energy in the cell because the net energy on glucose is much higher than that in lactose
What is a constitutively expressed enzyme and what is an example of one?
- They are enzymes that are being made, or are on all the time, an example is glycolytic enzymes
What is an example of an enzyme that is induced, or only turned on when needed?
beta-galactosidase
What are the effects that cAMP has on the growth rate of E. coli on various carbon sources?
- as growth rate slows, levels of cAMP increases
- cAMP levels are low in glucose
- cAMP levels are high in lactose, arabinose and glycerol
- cAMP binds to the regulatory protein
- the levels of cAMP depends on rates it’s synthesized and rates it’s degraded
What inhibits the activity of the enzyme that synthesizes cAMP?
glucose
What is the name of the enzyme that synthesizes cAMP?
adenylate cyclase
What is required for maximal initiation of the lactose operon and other operons that code for enzymes required for sugar metabolism in E. coli?
the catabolite activator protein (CAP)
What is present when the operon is off because the CAP is not bound?
glucose and lactose
What is present when the operon if off both becaue lac repressor bound and because CAP not bound?
glucose
What is present when the operon is turned off because of just the lac repressor being bound?
nothing (neither glucose or lactose)
What is present when the operon is on?
lactose
When is the only time you see transcription from lactose operons?
when just lactose is present
What causes the RNApolymerase to pause?
a hairpin loop in the RNA
What does a rho-independent terminator contain?
an inverted repeat followed by a string of approximately six adenine nucleotides
When does transcription terminate?
when inverted repeats form a hairpin followed by a string of uracils
How does rho-independent and rho-dependent terminators differ?
in the GC content of the stem structure and the uracils in the RNA hydrogen-bonded to the adenines of the DNA template
What are the steps of rho-dependent termination of transcription?
1) rho binds to an unstructured region of RNA and moves towards its 3’ end, following RNA polymerase
2) when RNA polymerase encounters a terminator sequence, it pauses and rho catches up
3) using helicase activity, rho unwinds the DNA-RNA hybrid and brings transcription to an end
What does a mutation in the sequence of a rho-independent termination result in?
the dependence of termination of rho at this site
Depending on the abundance of rho, different mRNAs are produced generating what?
different polypeptides encoded by a single operon
