prokaryotic gene transfer

Question 1

what are the three types of genetic transfer

Answer 1

transformation, transduction, conjugation

Question 2

what is transformation

Answer 2

uptake of naked DNA molecule/fragment by a competent cell from the environment, and the DNA is incorporated into the recipient chromosome in a heritable form. free dna is found when bacteria lyse and the fragments can be large and contain many genes

Question 3

describe competency when it comes to transformation

Answer 3

bacteria must be in certain pahse of growth- natural transformation only occurs in certian G pos and G neg genera i.e streptococcus (g pos) haemophilus (g neg)

Question 4

describe transformation mechanism

Answer 4

in s. pneumoniae a competent cell binds to DNA molecule. the molecule is cleaved by endonuclease to small fragments 5-15kb

one strand is hydrolysed by exonuclease., other moves through plasma membrane + integrates by recombination

Question 5

how does transformation differ in haemophilus

Answer 5

no production of competence factor, DNA uptake is only from closely related species. DNA is taken in by membrane vesicles. transferred DNA must have a special 11bp sequence

Question 6

what are the limitations of transformation

Answer 6

• limits on host range of the transfer and maintenance mechanism
• limited abiloty of foreign DNA to integrate dur to a lack of sequence similarity
• recipient restriction enzyme activity

Question 7

how can artificial transformation take place

Answer 7

two methods
- heat shock with CaCl2 treatment or electroporation
- high concentration of DNA used
- DNA inserted into plasmid

Question 8

what is conjugation

Answer 8

transfer of DNA by direct cell to cell contact

Question 9

how was conjugation doiscovered

Answer 9

discovered in lederberd and tatum in 1946 via plate method (like we did in lab)

was also demonstrated in 1950 by Davis in a U tube experiment

Question 10

describe fertility factor plasmids

Answer 10

aka F factor- tend to be 100kb long. have genes for pilus formation and gene transformation.

three types
F+: F factor alone autonomous (only has the tra gene)
F’: Factor autonomou with additional genes (has tra genes and special genes i.e antibiotic resistance)
HFr: integrated F factor plasmid (is inside the chromosome and is carried with the bacterial cell)

Question 11

what is a criteria of recipients

Answer 11

must lack the F plasmid- the donors will not conjugate with other donors

Question 12

describe F+ and F- matings

Answer 12

pilus forms between the two cells, extending from F+ cell. a single strand of the F factor moves through the pilus. each strand us replicated. F- becomes F+

Question 13

describe HFr and F- mating

Answer 13

F factor is integrated into the plasmid. Transfer begins with a nick in F factor at the origin of transfer. the chromosome moves through while replicating. since only part of F factor is transferred, the F- does not become a donor

Question 14

F’ and F- mating

Answer 14

F’ occurs due to imprecise excision of integated F plasmid from the chromosome- this mating is virtually identical to F+ and F-

Question 15

what happens during interrupted mating exps

Answer 15

the chromosome moves from donor to recipient at a constant rate, and in an interrupted mating exp the conjugation bridge is broken at various intervals by mixing the culture.

the order and timing of the gene transfer can be determined becuase they are directly reflected in the genes on the chromosome

Question 16

what is transduction

Answer 16

is a transfer of genes via bacterial viruses

Question 17

what are the two replications of a phage

Answer 17

reproductive lytic cycle
dormancy lysogenic cycle

Question 18

what happens in lytic cycle

Answer 18

absorption, penetration, DNA replication, protein synth, assembly, release and is usually caused by a virulent phage

Question 19

what happens in dormancy lysogenic cycle

Answer 19

absorption, penetrationm integration into bacterial chromosome, multiplication along with chromosome. usually happens with a temperate phage

Question 20

what are the two types of transduction

Answer 20

generalised and specialised

Question 21

describe generalised transduction

Answer 21

occurs as result of lytic cycle- any random segment of DNA can transfer

Question 22

describe specialised transduction

Answer 22

occurs due to lysogenic cycel- only genes adjacent to integrated virus are transferred

Question 23

describe the process of genealised transduction

Answer 23

the bacteriophages can pick up any portion of the hosts genome.

bacteriophages pick up fragments of donor bacteria degraded DNA. the bacteriophages are released and can infiltrate a recipient bacteria where it donates the donor bacterium’s DNA to the recipient bacterium

Question 24

describe specialised transduction

Answer 24

during spontaneuous excision, small piece of the donor bacteriums DNA near the bacteriophage insertion site is picked up and replaces some of the phage genome.
these bacteriophages adsorb to a recipient bacterium and injects its genome. the foreign DNA is inserted into the recipient bacterium’s nucleoid