Mechanisms of Genetic Variation and Bacteriophage and Genetic Exchange

Question 1

Mutations occur as a consequence of (3):

Answer 1

1. Errors in the replication process.
2. Direct damage to the genetic material by light or chemical agents.
3. Errors made by the mutation repair systems.

Question 2

DNA repair mechanisms (4):

Answer 2

1. Photoreactivation
2. Excision repair
3. Recombinational repair
4. Dimer bypass/Error prone repair

Question 3

Photoreactivation:

Answer 3

A single light-inducible enzyme, photolyase, recognizes pyrimidine dimers and splits the cyclobutane ring formed between pyrimidines.
- Error free.

Question 4

Excision repair:

Answer 4

uvrABC recognizes mispaired basses in the helix and nicks both sides. DNA pol I fills in the empty space. DNA ligase seals the nick.
- SOS response.

Question 5

Recombination repair:

Answer 5

Chromosome is replicated into two chromosomes, one will have a single stranded region with DNA damage, the other is normal.
A section of the normal DNA is used to repair the damaged daughter strand by recombination (patching).
- Error proof.

Question 6

Dimer bypass/Error prone repair:

Answer 6

DNA Pol III inserts any bases into the daughter strand across from a dimer or other damaged DNA.
- umuC and umuD are believed to modify the fidelity of DNA Pol III

Question 7

Induction of DNA repair systems:

Answer 7

1. RecA protease is activated by damage to DNA.
2. RecA protease cleaves and inactivates lexA repressor protein.
3. This cleavage results in the induction of all the genes in SOS regulation.

Question 8

Reciprocal recombination:

Answer 8

Recombination in which no genetic information is lost in the products.

Question 9

Gene conversion:

Answer 9

Crossover events that result in gain/loss of genetic information as a consequence of the resolution of the heteroduplex region.

Question 10

Two requirements for generalized recombination:

Answer 10

1. Homologous sequences.

2. recA, recBCD and other rec gene products

Question 11

Insertion element:

Answer 11

Transposase gene is flanked by short inverted repeats.

Question 12

Composite transposon:

Answer 12

Resistance gene(s) flanked by insertion elements.

Question 13

TnA family:

Answer 13

(Transposase, resolvase + drug resistance) flanked by inverted repeats.

Question 14

Host restriction:

Answer 14

Degradation of foreign DNA by the host cell.

Question 15

Bacteriophage host specificity:

Answer 15

• Host range is dependent on presence of receptors on host cell wall and presence of specific components of the host replication and transcription apparatus.

Question 16

Virulent phage infection:

Answer 16

Phage infection invariably leads to lysis of host organism.

Question 17

Temperate phage infection:

Answer 17

Phage infection may lead to ether host cell lysis or lysogeny.

Question 18

Lysogeny:

Answer 18

State of dormancy for the phage.

Question 19

Concatamers:

Answer 19

Many linear unit length genomes that are covalently linked together.

Question 20

Lysogenic conversion:

Answer 20

Prophage introduces new genes that are expressed in the host and impart novel phenotypes.

Question 21

Transformation:

Answer 21

The uptake of naked DNA into a cell followed either by recombination with the host genome or self-replication

Question 22

Transfection:

Answer 22

The uptake of naked bacteriophage DNA by cells, followed by the production of phage particles or lysogeny.

Question 23

Transduction:

Answer 23

The process of transferring host cell DNA sequences by bacteriophage to a recipient cell.

• Generalized
• Specialized

Question 24

Generalized transduction:

Answer 24

1. Bacterial DNA is degraded and pieces are mistakenly packaged into phage heads.
2. Phage injects DNA into host bacteria; DNA can recombine with host genome by generalized recombination.

Question 25

Generalized transducing phage:

Answer 25

Phage that can package random segments of the bacterial chromosome and introduce these segments into the host organism.

Question 26

Specialized transduction:

Answer 26

When a prophage excises improperly and an adjacent region of the host genome is attached to the phage chromosome.
- Specialized transducing phage.

Question 27

Conjugation:

Answer 27

The transfer of DNA from a bacterial cell of one mating type (male) to cell of the other mating type (female).

Question 28

F factor can exist in 3 different states inside the cell:

Answer 28

1. F+ plasmid
2. Hfr chromosome
3. F’ plasmid

Question 29

Self-replicating plasmid (F+):

Answer 29

Circular DNA molecule that replicates independently while the bacterial chromosome is replicating.

Question 30

Hfr chromosome:

Answer 30

F plasmid integration into host chromosome.

Question 31

F’ plasmid formation:

Answer 31

F plasmid can excise imprecisely from an Hfr chromosome and take bacterial genes with it.

Question 32

Type I excision:

Answer 32

Results in a portion of the F plasmid being left behind in the bacterial chromosome and a portion of the bacterial chromosome being attached to F.

Question 33

Type II excision:

Answer 33

Recombination between flanking bacterial sequences such that no F sequences are left behind and that bacterial sequences from both sides of the integration site are now on the F’ plasmid.