Practical 10: Gene transfer and antibiotic resistance in bacteria

Question 1

movement of DNA from one bacterial cell to another takes place by what three main horizontal gene transfer mechanisms

Answer 1

transformation
transduction
conjugation

Question 2

describe transformation

Answer 2

transformation occurs when bacteria take up exogenous DNA (DNA released into the environment when cells die or when it is secreted out through pores in bacterial cell membranes) and add it to their own genetic repertoire

Question 3

what is meant when is bacteria is described as being competent

Answer 3

the have the innate ability to take in exogenous DNA

Question 4

what is transduction

Answer 4

DNA is transported from one cell (the donor) to another (the recipient) by a virus

Question 5

how do phages reproduce

Answer 5

by injecting their DNA into bacteria , there the DNA replicates using the bacteriums enzymes to produce many more copies, the phage dna then instructs the bacterium to make more coat proteins and these associate to form new phages, each containing a new copy of the ohage genome. the new phage particles are then released from the bacteria cell and go on to infect new cells

Question 6

how does a phage become a carrier of foreign DNA and how does a bacteria come to possess it

Answer 6

a phage will by accident incorporate a piece of bacterial DNA instead of its own, so when this recombinant phage infects a new bacterium it will inject DNA from its previous bacterial host instead of its own DNA. DNA is then incorporated into the genetic repertoire of the recipient bacterium

Question 7

describe conjugation

Answer 7

first plasmid genes direct the bacterium to produce conjugative pili, which are long protein filaments that pull aa recipient cell in and form a conjugation bridge. a copy of the plasmid DNA can then pass. once inside the recipient cell the plasmid dna then recicularises and replicates to become double strandned.

Question 8

what is meant by transconjugant

Answer 8

the new recipient of dna via conjugation is called a transconjugant. it too can carry out conjugation

Question 9

how do antibiotics cause antibiotic resistance

Answer 9

can increase the transfer of resistance genes between bacteria eg by reducing the barriers to gene exchange for enzyme by breaking down the cell wall DNA can move in and out of the cell