T3- M1&2 Flashcards
What type of environment does prokaryotic growth need
A nutrient rich environment containing amino acids and carbs
Describe housekeeping genes
Their DNA has genes always required for function
What are housekeeping genes required for
General maintenance
What do housekeeping genes include
- structural proteins
- ribosomal proteins
Define regulated genes
Genes that can be turned on/off on demand
- expressed only when needed
Are enzymes housekeeping or regulated genes
Regulated
Why must cells metabolize energy
For ATP and other energy sources
What is the preferred energy source in E coli
Glucose
What happens once glucose is used up in bacteria
Growth is stopped
What do bacteria metabolize when glucose runs out
Lactose
What activates the switch to lactose
Products of glucose metabolism
Why aren’t lactose enzymes before glucose runs out
It would be a waste without lactose
What happens if lactose is present without glucose
Bacteria can quickly uptake lactose metabolizing genes to accommodate for new environment
What enzyme is needed to metabolize lactose
Beta galactosidase
What does lactose break down into
Glucose and galactose
Can beta galactosidase be made with glucose in cell
No
What did Jacob and Monod do
Grew E coli in lactose free medium, added it and removed to see if protein production changed
What pattern did Jacob and Monod see
There was a steady increase in response to more lactose
What did Jacob and Monod conclude
Figured out how bacteria controlled the production of an enzyme called beta-galactosidase
Does gene expression mean transcription?
No
Define gene expression
Functional product of gene is made, modified and activated
What does transcriptional control allow
transcription of DNA to mRNA
What does translational control allow
Translation of mRNA to protein
What does post translational control allow
Modification and activation of produced protein
What does transcriptional regulation control
Amount of mRNA produced
What does activation of transcription require
Binding to promoter and increase binding of RNA Polymerase
How is the gene turned off and on
Controlled binding of protein to promotor
Rank transcriptional regulation from slowest to fastest and why
Slowest- starting from scratch!
- relevant with drastic changes
What is an example of transcriptional regulation
When cell runs out of glucose and lactose metabolism is needed
Is transcriptional regulation efficient?
Yes! It does not use resources unless necessary
How is translation initiated in eukaryotes?
Binding of ribosome to 5’ cap and first AUG start codon
How is translation initiated in prokaryotes?
Ribosome binds and begins translation at Shine Dalgarno sequences
What does the rate of translation effect
Amount of protein produced
What does protein production depend on
Stability of mRNA
What does post translational control allow the polypeptide to do
Fold and be further chemically modified
How does post translational control effect protein activation
Cause proteins to be active/inactive by driving it into complexes, substrate binding, unmasking enzymatic domains
Rank post translational control from slowest to fastest
Fastest
How does post trans control respond to changes
Quick
Define enhancers
Short region of DNA that can be bound by proteins to increase the likelihood that transcription of a particular gene will occur
At what level does E coli regulate beta galactosidase
Transcriptional level
When is there activation in gene expression for beta galactosidase and lactose permease
When there is no glucose present in cell
What is lactose permease
A transport protein
Where does lactose permease sit
In the bacterial cell membrane
What does lactose permease do
Allows transport of lactose into cell
What is beta galactosidase
Cytoplasmically situated bacterial enzyme
What does beta galactosidase do
Cleaves imported lactose into glucose and galactose
Why are lactose permease and beta galactosidase linked
Because of functional relatedness
What does clustering genes with one operon do
Allow ability to control transcription of whole gene cluster as one unit
Who discovered the operon model
Francois Jacob and Jacques Monod in 1961
What does the operon model describe
Functionally related bacterial genes are organized into transcriptional units along bacterial chromosome
What controls the on and off of a gene
The operon
What does the operon consist of
The promoter, operator, and coordinated gene cluster whose products function in similar way
What is an operator
A sequence of nucleotides at beginning of operon that can be regulated to inhibit or allow transcription
What happens when operator is not bound to inhibitor
RNA polymerase can bind to operator and transcribe genes in protein
Why can bacteria produce separate polypeptides during translation
Because the polycistronic mRNA is punctuated with stop and start codons
What is the lac operon
Model for transcriptional regulation in prokaryotes such as E coli
What is under control in lac operon
Beta galactosidase and lactose permease expression
What regulatory sequences exist in lac operon
Promotor- binds RNA polymerase
Operator (lac O)- binding site for repressor protein expressed by lacI
What are the two main structural genes that code for lactose metabolism
lacY and lacZ gene
What does the lacY gene do
Codes for lactose permease which will be embedded in the cell membrane
What does the lacZ gene do
codes for beta galactosidase which cleaves lactose into glucose and galactose
What does lacI do
Controls expression of lacZ and lacY gene
How does lacI control expression
Codes for repressor proteins which binds to operator and inhibits transcription
What does the repressor protein do to stop transcription
Binds to operator region of operon so RNA polymerase cannot bind
When is the repressor protein expressed
During low levels of lactose
Define negative transcriptional regulation
Ability of repressor protein to inhibit transcription
How is expression of repressor protein when there are high levels of lactose
High expression to inhibit
Describe the structure of the repressor protein
Tetrameric protein
How does repressor protein inhibit
Binds to lacO so RNA cannot bind
How does lactose act as inducer
Binding to repressor protein on lac operon and causing change to repressor- so it cant bind with DNA
What happens when operator is not bound by repressor
RNA polymerase can bind and produce b galactosidase and lactose permease
What type of feedback is regulation of lac operon
Positive regulation
What increases as glucose levels decrease
Intracellular cyclic AMP
What does intracellular cAMP do
Increase of cAMP contributing to positive regulation of lac operon
What is a good indicator of nutritional state of E coli cells
Concentration of cAMP
Define adenylyl cyclase
Catalyzes the production of cAMP from ATP
How is adenylyl cyclase effected when glucose levels are high
It is inhibited
How are cAMP levels when glucose is low
High due to increased activity of adenylyl cyclase
How are cAMP levels when glucose is high
Low due to decreased activity of adenylyl cyclase
What protein does positive regulation of lac operon include
CRP (cyclic AMP Receptor Protein) or CAP (Catabolite Activator Protein)
What does CAP do
protein that binds to the promoters of operons that control the processing of alternative sugars, such as the lac operon
What happens when CAP bound by cAMP
It will bind to different site on bacterial DNA called CRP-cAMP or CAP-cAMP
How does cAMP respond to elevated signals
cAMP binds to CRP protein as allosteric activator
What happens when CRP-cAMP complex binds to bacterial DNA
Activate transcription of beta galactosidase and lactose permease in presence of lactose
What do low levels of glucose do to cAMP
Increase cAMP levels to activate positive regulator CRP-cAMP
What happens to repressor in negatively regulated transcription
A repressor will bind to operon to prevent polymerase from binding
Inducer proteins become..?
Inducer of genes
What happens to activator protein in positive regulation and why?
Binds to activator binding site on DNA
- allows for recruitment of RNA polymerase to promotor and initiation of transcription
What happens if activator is absent or cannot bind?
Transcription cannot occur
How is lac operon regulated in low glucose
Positively regulated
How is lac operon regulated in high glucose
Negatively regulated
