Bacterial Genetics

Question 1

Describe the General Secretion Pathway (post-translational).

Answer 1

1. The chaperone SecB takes the protein to the docking protein SecA.
2. ATP is hydrolyzed; Protein pushed through translocon (SecYEG).

Question 2

Describe the Signal Recognition Pathway (co-translational).

Answer 2

Energy required (GTP); Target proteins to CM

1. Signal recognition particle binds signal sequence
2. Protein is pushed into translocon (SecYEG)

Question 3

Are bacteria haploid or diploid?

Answer 3

They are haploid

Question 4

How do bacteria acquire genetic variation?

Answer 4

Random mutations and Acquisition of new DNA by horizontal gene transfer.

Question 5

What are types of mutagens?

Answer 5

Chemical, Radiation and viruses.

Question 6

What are the types of chemical mutagens?

Answer 6

Nucleotide analogues, Frameshift mutagens (Dna intercalating agents)

Question 7

What are the types of DNA repair?

Answer 7

Direct DNA repair, Excision repair, Post-replication repair, SOS response, and Error-prone repair.

Question 8

What does Direct DNA repair fix?

Answer 8

A single damaged nucleotide.

Question 9

What does Excision repair entail?

Answer 9

A segment of damaged DNA is removed and replaced.

Question 10

What does post replication repair do?

Answer 10

Involves recombination with homologous sequences.

Question 11

What is the SOS response?

Answer 11

An inducible DNA repair system.

Question 12

Describe error prone DNA repair.

Answer 12

It replaces accuracy with speed.

Question 13

What are the 3 types of genetic exchange in bacteria?

Answer 13

Transformation, Transduction and Conjugation.

Question 14

What is transformation?

Answer 14

The uptake of naked DNA from the environment; Need competent recipient cell.

Question 15

What are the steps to transformation?

Answer 15

1. Binding of exogenous DNA to cell surface.
2. Uptake of donor DNA into cells
3. Recombination with the recipient cell genome.

Question 16

What is Transduction?

Answer 16

Transfer of DNA from donor to recipient cell via bacteriophage. Bacteriophages are either lytic or lysogenic.

Question 17

What are the 2 types of transduction?

Answer 17

Generalized and Specialized transduction.

Question 18

Describe Generalized Transduction.

Answer 18

Lytic phage destroys host cell DNA. Small fragments of host cell DNA can be packaged into phage heads as new phage particles are formed. These pieces of bacterial DNA can be injected into new host cells when the virus infects. This is a low frequency transduction.

Question 19

Describe Specialized Transduction.

Answer 19

Lysogenic phage infects host bacterial cell. Prophase integrated in host cell genome. When prophage excises to produce new virions, it could pick up pieces of host cell chromosome. These genes co-integrate into the chromosome of a new recipient cell along with phage genome.

Question 20

Describe the transduction frequencies in specialized transduction.

Answer 20

The initial event of picking up bacterial DNA occurs at low frequency. Once a phage has picked up the DNA, all progeny phage will carry it as well and introduce it into new hosts at High frequency.

Question 21

Describe bacterial conjugation.

Answer 21

Plasmid mediated transfer of DNA from donor to recipient cell by direct contact; Governed by plasmid genes.

Question 22

Describe standard conjugation.

Answer 22

Conjugation between F+ and F- cells. Involves replicative transfer of DNA. One strand directs synthesis of its complement within donor cell. Other strand is transferred to the recipient cell, where its complementary strand is synthesized. Plasmid recircularizes and replicates independently in the recipient cell. Results in high frequency transfer of plasmid but not of host chromosomal genes. Both cells are F+

Question 23

Describe conjugation involving an Hfr donor

Answer 23

The F plasmid is integrated into the host chromosome. Incomplete transfer of F plasmid sequence leaves recipient cell F-; Donor remains Hfr.

Question 24

What are the fates of transferred DNA?

Answer 24

1. Degraded by nucleases.
2. Stabilization by circularization (plasmid)
3. Integration into host chromosome