Ch 15: Regulation of Gene Expression Flashcards
2 levels of a metabolic pathway can be controlled
- cells can adjust the activity of enzymes already present, can be based on supply
- cells can adjust the production of certain enzymes
operon model
control of gene expression in bacteria
nucleoid
In Prokaryotes, bacteria are found in a dense region of DNA called a nucleoid
3 ways genetic recombination in bacteria
- transformation
- transduction
- conjugation and plasmids
Transformation
- Uptake naked, foreign DNA from the surrounding environment, incorporated into it’s genome
- DNA from a cell that has broken open
- Important in biotechnology as a way getting bacteria to make proteins for humans (Insulin and HGH)
Transduction
- Phages carry bacterial genes from one host to another
- **Happens when bacterial DNA is accidentally packed in a capsid**
Conjugation and Plasmids
- Directs transfer of genetic material(sex reproduction), through a pilus
- Must have a segment of DNA called F factor, can be DNA or plasmid(small, circular, self-replicating, separate DNA molecule)
- F Plasmid contains about 25 genes
- Only one bacterium passes along DNA
- Pass either DNA or Plasmid
R Plasmid and Antibiotic Resistance
- Antibiotic Resistance is passed from one bacterium to another by the passing of plasmids
- A plasmid can have up to 10 different resistance genes
Responding to environmental change by regulation gene expression
A bacterium can tune its metabolism to the changing environment and food sources
trp
- naturally, trp operon is on and genes for tryptophan are transcribed
- when tryptophan is present, binds to the trp repressor protein which turns the operon off
- the repressor is only active when its corepressor tryptophan is present, the operon is turned off if the tryptophan levels are high
coordinately controlled
where genes are grouped and they are turned off and on with one switch, E Coli synthesizes the proteins at once
operator
the on-off switch is bounded too by repressor to turn off, positioned within the promoter
operon
operator + promoter + the genes they control, trp operon is naturally turned on
repressor
binds to the operator and blocks the attachment of RNA polymerase to the promoter, prevents transcription of the genes
regulatory gene
codes a repressor protein, upstream from the operon, repressor does not permanently bind since it is reversible, is also allosteric(is inactive and active)
corepressor
cooperates with the repressor to switch an operon off
repressible operon
it can be inhibited when a specific small molecule binds allosterically, trp operon is a repressible operon, anabolic
inducible operon
usually off but is turned on when a specific small molecule interacts with a different regulatory protein, catabolic
inducer
a small molecule that inactivates the repressor
Steps of lac operon reg
- lac operon(inducible) contains genes that code for enzymes for breaking down of lactose
- lac repressor is naturally active and switches the lac operon off
- the inducer(alactose) inactivates the repressor to turn the lac operon on
inducible enzymes
synthesis is induced by a chemical signal(lac)
repressible enzymes
the molecule is added to repress it(trp)
negative control
operons are switched off by the active form of their repressors
activator
a protein that binds to DNA and stimulates transcription of a gene, CRP