lecture 11: bacterial genetics

Question 1

describe the bacterial chromosome

Answer 1

-double stranded (ds), circular DNA molecule
-found in nucleiod region
-contains essential genes for survival

Question 2

what is a plasmid?

Answer 2

-small circular ds DNA molecule
-genes are not required for survival, but can give bacteria an advantage under changing environmental conditions (ex: antibiotic resistance)

Question 3

what is the bacterial genome composed of?

Answer 3

bacterial chromosome and plasmid

Question 4

what’s an episome?

Answer 4

segment of DNA that can exist as a plasmid or be integrated into bacterial chromosome

Question 5

are plasmid genes required for survival?

Answer 5

no!

Question 6

how do bacteria replicate?

Answer 6

by binary fission

Question 7

what is binary fission?

Answer 7

way in which bacteria replicate. its the simplified version of mitosis. single origin or replication, no telomeres, no introns, no spliceosome

Question 8

how does binary fission happen?

Answer 8

Question 9

what is interesting about genetic recombination?

Answer 9

can produce new bacterial strains

Question 10

what is genetic recombination?

Answer 10

combining DNA from 2 different sources

Question 11

what are the 3 methods of genetic recombination?

Answer 11

1) transformation (griffith, DNA from experiment)
2) transduction (via bacteriophage)
3) conjugation (bacteria to bacteria)

Question 12

what is transformation?

Answer 12

-bacterial cells take up foreign DNA from environment (ex: plasmid)
-foreign DNA can remain as a plasmid or be incorporated into the bacterial chromosome by recombination

Question 13

what is an example studied of transformation in bacteria?

Answer 13

-harmless R cells becomes transformed to a pathogenic strain when they take up DNA from S-cells

Question 14

once foreign DNA is taken into a cell via transformation, what are the 2 options for this DNA?

Answer 14

can remain as a plasmid in the cell or it can be incorporated into the bacterial chromosome by recombination

Question 15

what is transduction?

Answer 15

-genes are transferred from one bacterium to another by bacteriophage
-occurs during lytic cycle

Question 16

when does transduction happen?

Answer 16

during lytic cycle

Question 17

what does transduction result in?

Answer 17

the random transfer of genes

Question 18

how does transduction happen?

Answer 18

1) pieces of host DNA are packaged into bacteriophage during viral assembly
2) when bacteriophage infects new host, it inserts DNA from the previous host
3) recombination occurs between the introduced DNA and the bacterial chromosome

Question 19

what is conjugation?

Answer 19

-direct transfer of genes between 2 bacterial cells (like bacterial sex)

Question 20

what happens during conjugation?

Answer 20

1) donor cell extends an external appendage called the sex pilus
2) sex pilus attaches to recipient cell and a cytoplasmic bridge is formed between the 2 cells
3) DNA can be transferred across this bridge

Question 21

what is the F factor?

Answer 21

-it is the fertility factor. its a special piece of DNA that codes for the ability to form sex pili and transfer DNA
-segment of bacterial DNA that contains about25 genes involved in the production of sex pili

Question 22

where can we find the F factor in a chromosome?

Answer 22

-can be present as a plasmid or be incorporated into the bacterial chromosome (Hfr cells)

Question 23

what are hfr cells?

Answer 23

has f factor incorporated into bacterial chromosome

Question 24

what is the difference between F+ and F- cells?

Answer 24

F+:
-contain F factor in plasmid
-F factor is passed onto offspring
-can donate F factor

F-:
-lack F factor in plasmid
-can receive F factor

Question 25

what does conjugation look like?

Answer 25

Question 26

what happens during conjugation when the F factor is in the plasmid?

Answer 26

Question 27

what happens during conjugation when the F factor is in the bacterial chromosome?

Answer 27

Question 28

why are hfr very efficient at creating recombinant bacteria

Answer 28

because bacterial genes are delivered along with the F factor. in the case of non-hfr cells, most of the plasmid is the F factor, so doesn’t transfer much DNA other than F factor

Question 29

with conjugation with HFR cells, does the recipient cell always become F+?

Answer 29

no, transfer of DNA is random and depends on when connection is broken (recipient cell will not always become F+)