mechanisms of genetic exchange in bacteria

Question 1

how does transformation work

Answer 1

• one strand of viral DNA fragment enters the cell via transporter, and the other is hydrolyzed
• fragment pairs with the bacterial chromosome and recombination takes place.
• when the cell replicates and divides, one of the resulting cells is transformed and the other is not
  *not whole chromosome is transformed, just small section homologous to the gene

Question 2

competence

Answer 2

picking up material from the environment
- cells become competent from a gene on a chromosome that can synthesize a DNA transporter complex

Question 3

how can transformation be used to determine distance between bacterial genes

Answer 3

• if 2 genes are very close they will be present on the same piece of transforming DNA
• measured as a change in phenotype that occurs with a certain frequency
• the rate of cotransformation is proportional to the distance between genes

Question 4

transformation experiment in bacteria to determine distance between genes

Answer 4

1) DNA from a donor cell is fragmented
2) fragments are picked up by the recipient cell
3) the donor DNA becomes incorporated into bacterial chromosome through crossing over
4) genes that are close to one another are more likely to be present on the same DNA fragment and recombined together

Question 5

Fertility factor

Answer 5

• an episome that can exist as an extra-chromosomal DNA OR it can insert into the bacterial chromosome and replicate as part of it

Question 6

3 types of cells in conjugation

Answer 6

• F- cell (no F factor)
• F+ cell (autonomous F factor)
• Hfr cell ( integrated F factor)

Question 7

pilus

Answer 7

sticky arms that anchor recipient so it doesn’t float away when conjugation channel gets built

Question 8

mating and conjugation in F+ x F- crosses

Answer 8

• F+ and F- cells come together
• one strand of DNA is cleaved at the origin of replication of F factor
• rolling circle replication transfers one strand of F factor to recipient cell
• transfer of the F factor is completed, yielding 2 F+ bacteria

Question 9

what do genes on F factor code for

Answer 9

proteins to build conjugation channel

Question 10

conjugation of Hr and F- cell

Answer 10

• conjugation channel is formed between the cells
• F factor moves into F- cell and drags along some host chromosome genes from 5’
• the transferred strand replicates and crossing over takes place between donated Hfr and F- chromosomes
• may lead to recombination of alleles
• linear chromosome is degraded

Question 11

Conjugation experiment: determining order of alleles

Answer 11

1) transfer always begins within F, and the orientation determines the direction of transfer
2) in Hfr1, F is integrated between the leu gene and azi gene, so genes are transferred beginning with leu
3) in Hfr5, F is integrated between thi and his
4) F has opposite orientation in this chromosome, so genes are transferred beginning with thi

Question 12

conjugation between F+ and F- cells usually results in what?

Answer 12

two F+ cells

Question 13

how does transduction work

Answer 13

• bacteria are infected with the phage
• bacterial chromosome is fragmented and some bacterial genes are incorporated into new phages
• cell lysis releases transducing phages
• if the phage transfers bacterial genes to another bacterium, recombination may take place and produce a transduced bacterial cell

Question 14

transduction experiment in bacteria to determine distance between genes

Answer 14

1) a donor strain of bacteria that is a+ b+ c+ is infected with phage
2) bacterial chromosome is broken down and bacterial genes are incorporated into some of the progeny phages which is used to infect a recipient strain of bacteria that is a- b- c-
3) transfer of genes from the donor strain and recombination produce transductants in the recipient bacteria
4) genes close by are more likely to be cotransducted

Question 15

rolling circle replication