Bacterial genetics and gene regulation Flashcards
What prevents growth on a minimal medium?
A mutation that involves biosynthetic pathways
If a cell carries a mutation in a SPECIFIC GENE in the bio synthetic pathway what medium will it grow on?
A minimial medium with biosynthetic product added
What type of medium do wild type bacteria grow and synthesis on?
A MINIMAL medium
Is bacteria haploid or diploid?
Haploid
What are ‘prototrophs’?
Mutant bacteria that are wild type for a specific bio synthetic pathway
- Can grow on a minimal medium
What is a lac repressor?
- A protein that binds to the operator (upstream of lac operon) in the ABSENCE of lactose
- Prevents transcription
What happens when tryptophan levels are low?
- Greater expression of trp genes
- Trp repressor is inactive and unbound from the repressor
- RNA polymerase can bing to the promoter and transcribe genes
What are ‘tra genes’?
- Transfer genes
- Encode components of the transfer machinery (eg. F pilus proteins
How is genetic information exchanged between bacteria?
- Unidirectional
- DNA transferred across a physical bridge (F pilus) from the donor to the recipient
- DNA is in the form of an F plasmid
- Happens during conjugation
How do individual colonies from E Coli arrise?
From a single cell
What does the donor bacteria have that the recipient doesnt?
- Fertility factor
- Donor is F+
- Recipient is F-
What happens when tryptophan levels are high?
- Tryptophan binds to the trp repressor
- Activates the trp repressor
- Trp repressor binds the the operator
- Transcription of the trp genes is inhibited
What is conjugation and what is the process?
Bacterial mating which is controlled by the F plasmid
- Donor bacterium contains F plasmid
- Nicked strand of the F plasmid is transferred to the recipient cell
- Both the transferred and the remaining strands are copied
What are ‘auxotrophs’?
Mutant bacteria that can’t synthesise essential nutrients
- Can’t grow on a minimal medium
If a cell carries a mutation that INACTIVATE the bio synthetic pathway what medium will it grow on?
A complete medium but NOT a minimal medium
When do high frequency recombination strains arise?
- When the F plasmid recombines with the host chromosomal DNA (no F plasmid)
- Hfr donor chromosome is niked and transferred to the recipient cell
- Transferred DNA is recombined into the recipients chromosome (Hfr recombination)
What is the fertility factor?
A 100kb plasmid
What is an operon?
- A cluster of adjacent genes with closely related biochemical functions
- A set of bacterial genes controlled as a unit with a common promoter
- The genes usually involved in metabolic activities
What does changing the composition of the growth medium allow?
Genetic scanning for bio synthetic pathway encoding genes
What is a plasmid?
- Autonomously replicating DNA independent of the bacterial chromosomes
- Can be transferred from one bacterium to another
What is an inducible operon and name one?
- Presence of the metabolite turns the gene ON
- Lac operon (presence of lactose turns the genes on)
What is the trp operon?
- Genes which synthesise the enzyme for tryptophan synthesis
- trpE, trpD, trpC, trpB, trpA
What does a minimal medium contain?
- Simple carbon source
- Salts
- Trace materials
What is high frequency combination advantageous?
- Transfers more of the donor DNA to the recipient
- Very fast evolution for the recipient
When is the synthesis of the lac genes induced and blocked?
Synthesised when lactose is present
Blocked when lactose is absent and glucose (the breakdown product of lactose) is present
How is the lac repressor removed?
- Lactose binds to the lac repressor, causing it to dissociate from the operator
What is the lac operon?
A gene cluster that encodes proteins that enable lactose breakdown
What is the operator?
The site of DNA, upstream of a particular gene or operon which a specific repressor protein can bind and block the initiation of transcription at the adjacent promoter
What is a repressible operon and name one?
- Presence of the metabolite turns the operon OFF
- Trp operon (turned off in the presence of tryptophan)
What does the formation of Hfr donor chromosomes allow?
The emergence of prototrophic colonies from a mixed culture of 2 different auxotrophic mutants
What does a complete medium contain?
All molecules produced by biosynthetis pathways
- All amino acids
- All vitamins
- All nucleotides
What are the 2 principles of metabolic gene regulation?
1) Nutrient breakdown
2) Biosynthesis
What can bacteria synthesise on a minimal medium?
- Amino acids
- Vitamins
- Carbohydrates
What are the 3 clusters of genes in the lac operon?
lacZ+
- Codes for B-galactosidase
- Breaks down lactose -> galactose + glucose
lacY+
- Codes for lactose permase
- Facilitates passage of lactose across the phospholipid bilayer
lacA+
- Codes for B- galactoside transacetylase
- Transfers acetly group from Acetyl-CoA to B-galactosidase
What is the genetic transfer discovery?
1) Two strains of bacteria AUXOTROPH for two different biosynthetic pathways couldn’t grow on minimal medium
2) Mixing the colonies together resulted in their ability to grow on a minimal medium
3) However, it was revealed that it was required to have contact between the cells, not just to share a medium
4) Revealed that bacteria can share genes
