Bacteriology - Part II (genetics)

Question 1

Three mechanisms of genetic exchange in bacteria

Answer 1

• Transformation
• Transduction
• Conjugation

Question 2

Transformation

Answer 2

Live bacteria are able to pick up DNA from the environment containing virulence factors (these are released from dead bacteria)

• Donor/uptaken DNA is incorporated via homologous recombination
• produces recombinants and non recombinants

Question 3

Definition of homologous recombination

Answer 3

where regions of DNA that are homologous between the foreign DNA and the chromosome facilitate

Question 4

Gram positive bacteria that undergo transformation

Answer 4

• Bacillus substulis

- Strep pneumoniae

Question 5

Gram negative bacteria that undergo transformation

Answer 5

• Nisseria

- Helobacter

Question 6

Transduction definition

Answer 6

Transfer of virulence genes via bacteriophage

-Two types of phages: lytic phage and temperate phage

Question 7

Lytic Phage

Answer 7

insertion of phage carried DNA moves to hijacking and production of viral machinery and proteins
(leads to cell lysis)

Question 8

Temperate Phage

Answer 8

Can have a lytic OR lysogenic phase – lysogenic has the incorporation of viral inserted DNA into the bacterial genome

Question 9

During the formation of the viral genome for subsequent release from the bacteria, two things can occur:

Answer 9

Generalized transaction or specialized transduction

Question 10

Generalized transduction

Answer 10

(occurs during lytic phase): Any bacterial DNA is packaged into the capsid nonspecifically

Question 11

Specialized transduction

Answer 11

(lysogenic phse): Genes that are transduced are adjacent to the phage at site — thus are incorporated due to faulty excision of the prophage

Question 12

Effects of a prophage on bacteria

Answer 12

• Having prophage on board burdens with more DNA and may cause cell death (lytic cycle) when conditions change
• Advantages do exist: prophage protects from infection from related phages and can supply useful genes
• Antibiotic resistance
• Virulence factors

Question 13

Conjugation

Answer 13

• Exchange of plasmids between bacteria via direct contact – plasmids can contain virulence factors
• Plasmids are autonomous, circular DNA molecules – some can self transfer and others require “helper plasmids”

Question 14

transposition

Answer 14

• Mobile genetic elements that can inset themselves into and excise themselves from DNA
• Transposition does not require the donor and recipient DNA molecules be related&raquo_space;> thus can hop into any gene and disrupt it or provide a selective advantage