Lecture 13-14

Question 1

What are the two bacteriophages

Answer 1

T4 is lytic, lamba can replicate by lytic or lysogenic pathway ( in which it integrates into the host chromosome sby site specific recombintationat homlogous attachment sites), the integrated fro the the lamda phage is called in prophage

Question 2

What are plasmids

Answer 2

circluar DNA molecues that are often present in bacteria and can replicate independently of the bacterial chromosome, R plasmids contain genes encoding proteins that provide resistance to anibiotics, F plasmids contain proteins that allow gene transfer by conjugation

Question 3

Describe gene transfer by transofrmation

Answer 3

foregin DNA can be aquired by bacteria through transformation (uptake of free DNA through the cell walll: is sensitve to DNase), occurs in only some bacteria and reuiqresthe fomation of a recpetor/ channel complease (com proteins in Bacillus), one stand is degraded and the other undegoes homologous recombination in host hormosome

Question 4

Describe gene transfer by cojugation

Answer 4

conjugation (transfer from another bacterium throgugh a conjugation pore: requires cell-cell contact, requires a fertility factor (genetis elemnt tht encodes genes requires for conjugation) that can be presen on plasmid in F+ cells or invorportated into the host chormosomes in Hfr cells, during conjugation the conor cells pulls recipent into close contanst using cell surface appendages call pili, a conjustaion chelle is formaed connectin the two bacterainand the donone DNA is cunt at the OriT site, DNA replicaiton proceeds by roling cirlce mechanism reuslting in the transfer oof 1 strand to the recipient cell werhe the second strand is synthesies,

Chromosomal gnes can be mapped by intureeupted mathing between Hfr cells and F- cellls,

excision of a n F facor form the chromosome of a Hfr cells can in coms cases reuslt in the transfer of host chromosomal DNA to the F plasmis which can be trasferred to recipient cells (secudation)

Question 5

Describe genes transfer by transduction

Answer 5

transduction (by infection with a virus, does not reuqire cell contact and is not sensitve to DNase), random bits of host DNA are encapsulated into a phage coast and transfeered to a ceicipent cell or spicalizes (in which excision of the lmbda prophage can occur anomalously teusltin gin the inclusion of flanking chromosomal DNA

Question 6

Describe inerstion sequences (IS)

Answer 6

IS element have termial inverted repeated and an intevening sequence that encodes tha transoposase gene, tranposition invove sthe removal od the IS element for its oringainl state and insertion into a new sie by creating a staggered cut followed by inseration and gap filling which created a traget sit duplication

composite transposons are two close IS element

Question 7

Describe replicative transposons

Answer 7

transpose a mechanisms tha tincluse fusions of donor and recicpent DNA element followed by transoson replication, homolgous recombination and resoltuion that realses one of the element reuslting in the duplication fot the trasposon

Question 8

What are the categories of thransoible element in euks

Answer 8

non replicative ex. Ac/Ds (maize), P element in drosophilia

replicative (RNA intermendaites)

1. retrovirus like elemements,
   ex. copia (drosophil), ty1 (yeast)
   geneticalle resebly retroviruses but lack the gnes needed to spread outside the cells, these elemtne traspose by a mechansims that invovles the trancription of the lelemt, which reuireqs LTR sequence, followed by a reverse trancription of the RNA into DNA whcih is inserted into new position in the genome
2. restospsoons -> resemle mautre mRNA
   Lines and Sines
   make up a large percentage of genomes
   elementat lack LTR sequences, are trancribed from their own promoters by RNA pol II and are reverse trancribed into DNA whcih re-inserts into the chromosome