Lecture 10 Bacterial Genetics

Question 1

What makes up bacterial genome

Answer 1

circular chromosome several million bp in length

Question 2

How many bps does E. coli hav

Answer 2

4.6 million `

Question 3

What is special about vibrio cholerae

Answer 3

has two circular chromosomes

Question 4

What percentage of bacterial genome encodes proteins

Answer 4

90%

Question 5

How many plasmids does e.coli have

Answer 5

270

Question 6

What are episomes

Answer 6

plasmids capable of freely replicating and are able to integrate into bacterial chromosome

Question 7

What did Lederberg and Tatum demonstrate

Answer 7

that bacteria transfer genes in conjugation

Question 8

Describe lederberg and tatums experiment

Answer 8

• Auxotrophic Y10 and Y24 strain both were missing different genes for specific amino acid synthesis
• would not grown on their own
• when mixed together both of them grow demonstrating that exchange of genetic material occurred

Question 9

What does conjugation depend on

Answer 9

fertility factor present in donor cell and absent in recipient cell

Question 10

What genes are transfered in conjugation

Answer 10

only genes on the f factor

Question 11

Describe the process of conjugation

Answer 11

• cytoplasmic connection forms
• One DNA strand on the F factor is nicked at the origin and separates
• Replication takes place on the F factor replacing the nicked strand
• 5’ end of the nicked DNA passes into the recipient cell
• New single strand is replicated in the recipient cell
• produces a circular double stranded copy of plasmid
• F- cell becomes F+

Question 12

Describe the process of Hfr conjucation

Answer 12

• F s nicked and the 5’ end moves into the F- cell
• transferred strand replicates
• Crossing over takes place between donated Hfr chromosome and original chromosome of the F- cell
• May lead to recombination of alleles
• linear chromosome is degraded

Question 13

What are F’ cells and what can they induce

Answer 13

when an F factor does excise from bacterial chromosome and a small amount of chromosome moves with it

They can induce partial diploidy

Question 14

What is the process that F’ cells undergo

Answer 14

• Crossing over takes place within the Hfr chromosome
• When the F factor excises from the bacterial chromosome it may carry some bacterial genes with it
• During conjugation, the F factor with the bacterial gene is transferred to the F- cell
• Produces a partial diploid with two copies of the bacterial chromosome

Question 15

Describe the process of transformation in bacteria

Answer 15

• One strand of the double stranded DNA fragment enters the cell while the other is hydrolyzed
• the single stranded fragment pairs with the bacterial chromosome and recombination takes place
• the remainder of the single stranded DNA fragment is degraded
• when cell replicates and divides, one of the resulting cells is transformed and the other is not

Question 16

What did lederberd and zinder discover

Answer 16

transduction while working on salmonella

Question 17

What was the process of lederberd and ziderners experiment

Answer 17

• two auxotroph strains of salmonella were mixed and platted on minimal media
• some phototrophic colonies grew
• Two strains were placed in a davis U tube and allowed to mix through pores smaller than bacteria
• Phototrophic colonies were only obtained from one side of the tube
• lead to conclusion that genetic exchange did not take place through conjugation, a phage was later discovered to be the agent of transfer

Question 18

What was the implications of Seymore Benzers work

Answer 18

determined that different mutations within a gene could be mapped

Question 19

Why did seymore benzer need a large number of progeny

Answer 19

frequency of recombinants were used to map the rII phage mutants therefore needed a large number of progeny to generate enough recombinations

Question 20

What does plaque formation indicate when working with phages

Answer 20

host susceptibility to specific phage