What are the three levels at which prokaryotes can gene regulate?
- Transcriptional control: Regulatory proteins alter the ability of RNA polymerase to bind to the promoter and initiate transcription.
- Translational control: regulatory proteins interact with mRNA and affect it’s or interact with ribosomes to affect it’s stability, or interact with ribosomes to affect translation initiation or elongation.
- Post-translational control: chemical modifications to protein ( e.g. phosphorylation) affect its activity.
What are the pros/ cons of transcriptional control?
- least wasteful level of gene regulation, from the sense of if the cell no longer needs a protein then why waste ATP and other factors to transcribe the gene and translate the mRNA to make the protein in the first place.
- ——————————————————————————- negative: slowest way for a cell to change its behavior. because even if a cell stops transcribing a particular gene, any mRNA that were already made will continue to be translated for a while to make new proteins. Any protein that is made will continue to be active for some period of time.
What are the pros/ cons of post- translational control?
Positive: allows the fastest change in cell behavior.
because any protein that is present, once it is modified can then be switched on or off.
What is negative transcriptional control?
when some regulatory protein blocks transcription.
- a repressor protein binds to DNA and blocks RNA polymerase from initiating transcription.
What is positive transcriptional control?
- when a regulator protein triggers transcription
- in the presences of a positive transcriptional protein (activator protein), RNA polymerase binds stable to it and can then begin transcription.
What experiment test If every gene in the bacteria genome being constantly transcribed?
- what would you expect to happen?
Jaques Monod
- Escherichia coli, the most abundant e coli was studied in depth.
- They placed in different settings containing carbon, as that is coli’s primary food source.
- you would expect different forms of genes to be expressed in different arrays of carbohydrates to supply carbon energy.
What is beta-galactosidase?
What is it’s purpose in this chapter?
- enzyme that cleaves the disaccharide of Lactose.
- Jaques Monod was interested in its expression, and if bacteria would express this gene all the time or just in the presences of lactose.
Describe the experimental set up that Jaques Monod created?
- describe his results:
- He created three dishes, otherwise known as treatments, 1: glucose only, 2: glucose and lactose, 3: lactose only.
- the glucose and lactose serves as the carbon source.
- This allowed him to test the levels of beta-galactosidase expression in three different treatments.
——————————————————————————— Treatment 1: no beta-galactosidase - Treatment 2: no beta-galactosidase
- Treatment 3: Production of beta-galactosidase
PROVING: they can not only detect if lactose is in the environment, but a wide variety of other carbon sources so the can find the optimal one.
How did Jacob and Jacques Mondo identify what proteins encoded for the lactase gene?
- Genetic screen: take a large population of organisms and expose them to a chemical or environmental factor that will randomly induce them to mutations in their genomes.
2. ) - then you screen through that population to find individuals in the specific process you’re interested in. - took a population of E Coli that had been exposed to a mutagen of some kind, and then grew those onto plates containing glucose as the only food source.
- they took a block with velvet (basically something to extract the E coli and place them on a new plate containing Lactose as the only food source.
- Following this growth on plate number two, they looked at which cells grew only on the glucose media and failed to grow in the presence of lactose.
- Thus, those cells genes had a mutation and made them unable to metabolize lactase.
- then they would go back to the original plate and study the cells from the colonies that grew in glucose but failed to grow in lactose.
What is replica plating?
- you’re basically taking a copy of a plate via extracting cells from certain colonies that grew and placing on a different plate with a different media make up.
What genes are important in lactose metabolism?
Galactoside permease: transports lactose into the cell.
- B-Galactosidase: breaks down lactose inside the cell.
Describe the following genes in relation to the Jacques Mondo and Jacob experiment: lacZ, lacY, lacI:
lacZ: encodes B-Galactosidase
lacY: encodes Galactoside permease
lacI:
————————————————————————–
(mutant form:)
LacZ- : e-coli with a mutation that renders the LacZ gene inactive, so they don’t produce functional B-Galactosidase. ( Brings lactose in, but won’t be able to cleave it)
lacY- : renders Galactoside permease unfunctionable, and would fail to import lactose into the cell, in the first place, because it lacks Galactoside permease.
lacI- : expresses B-Galactosidase even if there is no lactose around,
What are the observable phenotypes of lacI-,lacZ-, and lacY- ?
lacI- : cells cannot cleave lactose, even in the presence of inducer ( lactose)
lacZ- : cells cannot accumulate lactose.
lacY- : cells can cleave lactose even if lactose is absent as an inducer.
what is the lac operon?
lacZ, lacY, lacA, Operator, promoter
operon?
physically adjacent genes encoding functionally-related proteins, and under common regulatory control
- you turn one on you turn them all on type of relationship.
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What is the operator sequence?
- It sits in between the lacZ region and the promoter.
what is true in the expression of the lac operon without the presence of lactose?
- Why does this happen??
- the lac operon isn’t expressed.
- The lacI gene, not in the operon is expressed all the time, which causes it to produce a suppressor protein.
- the repressor protein then binds to the operator sequence in the lac operon and prevents RNA polymerase from carrying out transcription.
what is true in the expression of the lac operon in the presence of lactose?
- Why does this happen??
- lactose is an allosteric regulator of the repressor protein.
- so after the lacI gene synthesis the repressor protein and it binds to the lactose, which causes it it to change its shape and not bind to the operator.
- this allows for RNA polymerase to carry out transcription and express the gene.
What is true in cells that lack a functional lacI gene?
- there is no repressor protein made.
- so these cells have their lac operon expressed all the time.
- Which is known as constitutive expression
what is constitutive expression?
high levels of expression that are unregulated.
Is the example of a cell not in the presence of lactose, thus causing the repressor protein to bind to the operator sequence and prevent expression of the lac operon a positive or negative transcriptional control?
- ## Negative: the regulatory protein is blocking transcription.
What is an inducer and what is an example of an inducer?
- an environmental signal that causes a change in expression.
- lactose is an inducer of the lac operon
how does the presence of glucose inhibit the expression of the lac operon?
- There are two key factors present:
- ## inducer exclusion and catabolite repression:
- inducer exclusion: high levels of the activity of the glucose transporter inhibit the activity of galactosidase permease. In other words, the more glucose is coming in, the less lactose.
high levels of glucose outside the cell, it is difficult for galactosidase permease to bring lactose inside the cell .
——————————————————————————– - catabolite repression: glucose inhibits transcription of the lac operon.
- catabolism: larger molecules are broken down into smaller pieces.
- ## i.e: B-Galactosidase breaking down lactose, meaning that glucose and galactose are catabolites of this reaction.
- It is important to understand Adenylyl cyclase’s role in this process: enzyme that takes ATP and strips it of two of the phosphate groups and uses that energy to sort of cyclize the molecule—-> cAMP.
- ## cAMP is a potent allosteric regulator of many kinds of proteins within the cell.pt2:
- there is a protein called cap and that binds to a regulatory sequence in the lac operon gene that is just infront of the promoter.
- when cap is bond to its regulatory sequence, cap site, then it promotes the stabile association of RNA polymerase with the promoter to make the transcription more likely, but cap only binds to the site when cAMP is present.
- ## cAMP is a allosteric regulator of cap, meaning it changes its shape so that CAP will bind to this other regulator site and in that configuration, cap helps to recruit RNA polymerase and stabilize it thus allowing RNA polymerase to be initiated.pt3:
- There is also an association between glucose and adenylyl cyclase.
- when glucose levels are high adenylyl cyclase levels are high, which means there is also very little cAMP inside the cell. Which also prevents the cap from binding to the cap site.
- So the inverse is true when glucose levels are low, thus low glucose = promotion of RNA transcription
Are all bacterial genes arranged in operons?
No, but genes that encode proteins that are involved in a common process are.
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Chapter 111
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Chapter 239
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CHapter 435
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Chapter 324
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Chapter 520
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chapter 613
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Chapter 6 Part 2: Membrane Permeability13
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Chapter 6 membrane proteins:6
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Unit 20
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Chapter 6 Part from uni 224
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Chapter 828
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Chapter 7:110
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Chapter: 9: prt: 1, 2, 352
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Chapter 9 pt: 4,533
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Chapter 10 Parts 1 & 233
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Chapter 10 Parts 3 & 436
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Unit 30
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Chapter 1164
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Chapter 1548
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Chapter 1246
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chapter 1369
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chapter 1434
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chapter 14 parts 3 & 422
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chapter 14 mastering5
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Unit 4:0
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Chapter `1626
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chapter 17:31
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Chapters 1829
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chapter 1935
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Unit 5:0
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Chapter 33 Pt. 1 (overview of viruses)14
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Chapter 33 Part 2:7
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Part 311
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Part 40
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Chapter 48 Pt 1.14
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Part 210
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part 3:16
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Part 413
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Part 513
