Bacterial Genetics and Genetic Variation

Question 1

Describe the genetic differences between Prokatyotes v Eukaryotic Genetic

Answer 1

Prokaryotes:
Single circular genome
Haploid
Extra-chromosomal plasmids
Cytoplasmic Location
Coupled transcription and translation

Eukaryotes:
Multiple linear chromosomes
Diploid
No extra-chromosomal plasmids
Within membrane bound nucleus

Question 2

What is coupled transcription translation?

Answer 2

Translation begins while the Mrna is still being synthesised

Question 3

What are the 2 types of how genetic information is passed on in bacteria?

Answer 3

Horizontal gene transfer- doesn’t have to be the same species or related, can be free DNA in environment, encoded from other things. PILI, creates variation.
Vertical gene transfer- binary fission, persists the variation

Question 4

What are the key genetic variations in bacterial populations?

Answer 4

Respond to new selective pressures

To survive adverse environmental conditions

To exploit new environment that it encounters

Question 5

What are some of the genetic changes that are passed on through VGT?

Answer 5

Spontaneous mutations
Single-nucleotide polymorphisms
Mutation rates are low—> slow driven by replication rate
Select out mutants-m. tuberculosis—->point mutations
point mutations can give rise to drug resistance

Question 6

What are the 3 main horizontal gene transfers?

Answer 6

1. Conjugation
   
   • Transfer of plasmids via pili
   2. Transduction
      - Transfer of DNA via bacteriophage (Virus)
   3. Transformation
      - Uptake of DNA from the environment

Question 7

What are some of the properties of bacterial plasmids?

Answer 7

Exre-chromosomal pices of DNA
small circular molecules
self-replicating
can be present in multiple copies

Question 8

What are some of the things the plasmid might encode for? (4)

Answer 8

Virulence
Antibiotic resisteance
Some toins
Genes that promotes adherence to host cells

Question 9

What is conjugation?

Answer 9

Donor’s F plasmid forms a pilus which extends to a recipient
Pilus attaches to the recipient
DNA polymerase: Plasmid copy released to the recipient
F plasmid copy present in the new donor meaning it can now form a pilus

If both bacteria have F plasmid, no pili will form/attach

Question 10

What is the life-cycle of a Phage?

Answer 10

Phage infectes a bacterium
Phage DNA circularizes
There are 2 pathways:
1. Lytic
2. Lysogenic

Lytic: Phage DNA replicates inside the bacterium, new phage particles are produced and lyse bcaterium—> lysis and release of phages.

Lysogenic: Phage DNA integrates with the bacterium DNA, bacterium grows as lysogen, phage DNA excites causing phage DNA replication—->New phage particles are produced and lyse bacterium—>Lysis and release of phage

Question 11

Whats the process of the formation of transdunctants?

Answer 11

Doner strain infected with phage
Rarely a phage head takes up bacterial DNA
Transducing particle containing only bacterial DNA
Recipient strain infected with the bacterial phage
Recombiant recipient—>transdunction
Bacteria-bacteria DNA exchange due to phage

Question 12

What is transformation?

Answer 12

Uptake of naked DNA from the environment
Can occur naturally or be induced artificially
- Important for molecular biology—> Heat shock, weakens the cell wall
Ø Conditions must be favourable
Ø Bacterial cells must be competent
Pure chance event

Question 13

What is the importance of horizontal gene transfer for bacterial pathogens?

Answer 13

Gene pool available for bacterial pathgens is much larger than originally throught (pangenome)

Allows for rapid emergence of bacterial pathogens

Allows for a single species to colonisediverse niches and cause a range of disease
diversity allows escape from antibiotic treatment or vaccination statergies
Big selection pressures can cause rapid emergence of bacterial pathogens

Question 14

Whats special about E.coli?

Answer 14

It has multiple strains that infect different parts of the body—> even the brain which has a barrier that shouldnt normally be prone to infection howver the E.coli surpasses that.

Question 15

Give some examples of why horizontal gene transfer in important?

Answer 15

Virulence factors:
- plasmids encoded heat-liable entertoxin of entertoxigenic E.coli
- PAI encoding haemolysin, pili and cytotoxins
- Phage encoded dtxR gene from C. diphtheriae
Transfer of antibiotic resistance in Gram -ve bacteria:
- Beta-lactamases plasmid encoded
- Chromosomally encoded beta-lactamases

Question 16

Whats the gene that causes extreme antibiotic resistance in some bacteria pathogens?

Answer 16

MCR1