Bacterial Genetics

Question 1

What is a spontaneous mutation?

Answer 1

A mistake during DNA replication can substitute one base for a different base

Question 2

What can a spontaneous mutation involve?

Answer 2

Can change a single amino acid, or add a stop codon and inactivate the whole protein

Question 3

What does removal or addition of a nucleotide change?

Answer 3

The translational reading frame

Question 4

Is it better to change one nucleotide, or a group of 3?

Answer 4

A shift or change of a group of 3 nucleotides has a less damaging effect on the strand.

Question 5

In which 3 ways can a mutation be induced?

Answer 5

UV or X-ray radiation, or chemicals that alter DNA

Question 6

What is the effect of vertical gene transfer on progeny?

Answer 6

All the progeny of that bacteria have the new DNA sequence

Question 7

At what rate do spontaneous mutations occur?

Answer 7

Occurs between 1 in 104 and 1 in 1012 in a given gene when a cell divides

Question 8

What are the names of the two types of “directional” gene transfer that contribute to bacterial diversity?

Answer 8

Horizontal and vertical.

Question 9

What are the 3 types of Horizontal Gene Transfer?

Answer 9

1. Transformation
2. Transduction
3. Conjugation

Question 10

What is Transformation?

Answer 10

The transfer of genetic material from transfer of naked DNA

Question 11

What is Transduction?

Answer 11

The transfer of genetic material from one bacterium to another by a bacteriophage

Question 12

What is Conjugation?

Answer 12

The transfer of genetic material from one bacterium to another by means of conjugation pili

Question 13

What are the 3 steps of Transformation?

Answer 13

1. Cells rupture during the stationary and death phase (The chromosome breaks into small pieces)
2. Recipient cell picks up piece of the naked DNA
3. The naked DNA is integrated onto the recipient chromosome

Question 14

What condition is required for natural transformation to occur?

Answer 14

Natural transformation occurs when bacterial cells are “competent”

Question 15

When is bacterial competence?

Answer 15

Competence is a condition in which bacterial cells are capable of taking up and integrating larger fragments of DNA

Question 16

When does bacterial competence occur?

Answer 16

During the late log, early stationary phase

Question 17

How can bacterial competence be induced?

Answer 17

By treating bacteria with certain chemicals/electric current.

Question 18

What is is a mis-packaging of DNA during viral replication, with regards to horozontal gene transfer, called?

Answer 18

Transduction

Question 19

What are the steps of Transduction?

Answer 19

1. Bacterial DNA that is transferred from donor to recipient via a bacterial virus (bacteriophage)
2. The mis-packaged phage infects a new bacterial cell and inserts the donor DNA into the recipient cell
3. The donor DNA is integrated and mis-matched pairs are repaired

Question 20

What are plasmids?

Answer 20

Extrachromosomal circular DNA found in bacteria (as well as Archaea and Eucarya)

Question 21

How many plasmids are found in each bacterium?

Answer 21

From 1-500

Question 22

Plasmids are readily transferred by . . .

Answer 22

Conjugation

Question 23

Give an example to illustrate that Plasmids are useful but not essential.

Answer 23

R Plasmids that confer resistance to many different antimicrobial medications

Question 24

Genes that code for resistance to three antimicrobials are called what?

Answer 24

Resistance

Question 25

Genes that code for transfer of the plasmid from bacteria to bacteria are what?

Answer 25

Resistance Transfer Factor

Question 26

What is Conjugation mediated by?

Answer 26

RTF (Resistance Transfer Factor) region of plasmid

Question 27

How do bacteria achieve direct contact between cells during Conjugation?

Answer 27

Via the sex or F pilus

Question 28

What is the plasmid that codes for a pilus on the donor cell?

Answer 28

The fertility factor or “F factor,” which is designated F+

Question 29

What is the designation of the Recipient cell, which does not carry a plasmid?

Answer 29

F-

Question 30

What are the 4 steps of conjugation?

Answer 30

1. Sex pilus of donor cell recognizes and binds specific receptor on recipient cell
2. Cells are pulled together
3. DNA is transferred (starting at origin of transfer region) to recipient [Single strand of DNA transferred, single strand left behind]
4. Synthesis of functional (double-stranded) plasmid in both donor and recipient

Question 31

What happens to the recipient cell after conjugation?

Answer 31

After the plasmid is transferred, the F- cell becomes F+

Question 32

What happens to the donor cell after conjugation?

Answer 32

Donor survives (as apposed to transformation and transduction)