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PoD Test 1 > Mechanisms of Genetic Variation > Flashcards

Mechanisms of Genetic Variation Flashcards

1
Q

What is the medical relevance of the fact that mutations occur prior to exposure to the selective agent?

A

Drug resistance occurs spontaneously

Use of antibiotics in animal feed selects and enriches for drug resistance organisms like Campylobacter

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2
Q

What is photoreactivation?

A

A single light-inducible enzyme called photolyase recognizes pyrimidine dimers and splits the cyclobutane ring formed ring formed between pyrimidines

Considered error-free pathway because original bases are restored

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3
Q

What is excision repair?

A

uvrABC exinuclease recognizes mispaired bases and nicks both sides of the damaged strand

DNA pol I fills the empty space and DNA ligase seals the nicks

error-free

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4
Q

What is recombination repair?

A

Postreplication

One daughter will have a damaged strand and normal strand, the normal strand is used to repair the damaged strand via recombination

Error-proof

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5
Q

What is error-prone repair?

A

Enzymes involved are induces as part of SOS response (DNA damage)

DNA pol III inserts any bases into the daughter strand across from a dimer or other damage

Advantage is daughter cells receive covalently closed circular chromosomes, albeit carrying a number of mutations

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6
Q

What is RecA?

A

Protease that is activated by damage to DNA

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7
Q

What is LexA?

A

Repressor of the SOS regulon

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8
Q

How are the DNA repair systems induced?

A

RecA is activated via DNA damage, which then cleaves and inactivates the lexA repressor protein

This results in the induction of all the genes in SOS regulon including the recA gene and DNA repair systems

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9
Q

What is homologous (generalized) recombination?

A

Exchange of genetic information between two genomes with identical or nearly identical sequences

Requires recA and recBCD proteins

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10
Q

What is site-specific recombination?

A

recA-independent exchange of information between genomes with limited sequence homology, ususally requires specialized recombination enzymes

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11
Q

What is reciprocal recombination?

A

A crossover event that usually results in two parental and two recombinant type ascospores

No genetic information is lost

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12
Q

What is gene conversion?

A

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

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13
Q

What is site-specific recombination?

A

Recombination events that are dependent on transposons and the use of specialized recombination enzymes

E.g. phage lambda integration

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14
Q

What are the consequences of transposition?

A

Transposons can inactivate genes by inserting into the coding portion or activate quiescent genes by providing a constituitive promoter

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15
Q

What is the difference between a simple transposon and complex transposon?

A

Simple transposons encode only a transposase

Composite transposons also contain genes for antibiotic resistance

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16
Q

How are complex transposons implicated in antibiotic resistance spread?

A

These complex transposons can jump from a chromosomal location to a plasmid which can be transferred to other strains by conjugation

17
Q

What is phase variation?

A

Antigen switching caused by site-specific inversion of a promoter than controls transcription of the two antigens

E.g. H1/H2 switching in salmonella

18
Q

What is the host range of a bacteriophage dependent on?

A

Presence of receptors on host cell wall and presence of specific components of the host replication and transcription apparatus

19
Q

What is lysogeny?

A

State of dormancy for the phage

Best equated with a state of dormancy and immunity to superinfection by identical or related phage, not integration of phage into the genome.

20
Q

What are concatamers?

A

Many linear unit length genomes that are covalently linked together

Generated during the lytic cycle of a phage to fill new phage capsids

21
Q

Describe the lysogenic mode of phage infection?

A

Circular DNA integrates into bacterial chromosome via site-specific recombination

Dormant prophage resides in bacterial chromosome until mutagenesis of the lysogenic bacteria

Breaking the lysogenic state allows the phage to escape compromised host

22
Q

Why is temperance (lysogeny) significant?

A

Allows the phage to safely spread as a passenger and escape deleterious agents in the process

23
Q

What is lysogenic conversion?

A

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

24
Q

What are merodiploids?

A

Partial diploid, required for recombination

Formed after all three types of genetic exchange in bacteria

25
Q

What is transformation?

A

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

26
Q

What is transfection?

A

Uptake of naked bacteriorphage DNA by cells, followed by the production of phage particles or lysogeny

27
Q

What is transduction?

A

Process of tranferring host ccell DNA sequences by bacteriophage to a recipient cell

Two types: generalized and specialized

28
Q

What is generalized transduction?

A

During the lytic process, DNA from the first bacteria genome is mistakenly packaged into the phage

The phage then goes on to infect another bacterium, transferring DNA from the first bacterium via generalized recombination

29
Q

What is specialized transduction?

A

A prophage excises improperly and an adjacent region of the host genome is attached to the phage chromosome

The phage then transfers this hybrid chromosome to a new host

Only one or a few specific genes can be transferred to the new host

30
Q

What is conjugation?

A

Transfer of DNA from a bacterial cell of one mating type to cell of another mating type

31
Q

What designates the donor or recipient bactieria?

A

Donor is determined by the presence of a transmissible plasmid called the F factor

Donors are F+ and recipients are F-

32
Q

What are the functions of the F factor?

A

Contains for the synthesis of F pilus

Encodes genes that enable its transfer to F- cells, Tra genes

Use host replication machinery

33
Q

What are the three different forms of F factor that can exist inside the cell?

A

F+ plasmid - circular plasmid that replicated independently

Hfr chromosome - F plasmid is integrated into the chromosome

F’ plasmid - F plasmid excises imprecisely from Hfr chromosome and takes bacterial genes with it

34
Q

What are R plasmids?

A

Closely related to F plasmids and carry genes that encode resistance to antibiotics

PoD Test 1 (31 decks)

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