Bacterial DNA repair systems

Question 1

What type of mutations are there?

Answer 1

SNPs
-silent (no change in aa prod)
-mis-sense (diff aa prod)
-non-sense (codon changed to stop codon)
Frame shifts
-insertions (eg. tns)
-deletions
Inversions (nat in bact)

Question 2

What is slipped strand mispairing?

Answer 2

aka replication slippage
Mutation process during DNA replication where template strand “slips” so that illegitimate base pairing occurs and bases are skipped
-occurs naturally in bact to gen genetic variation and turn genes on and off
-immune evasion (eg. not express surface prots so aren’t recognised by phages)

Question 3

How do mutations arise?

Answer 3

Spontaneously
-eg. tautomers (struct isomers) of bases arise during replication (prod imino form instead of amino form which can then base pair diff) or by reacting with water (deamination of C to U)
Induced
-EM radiation (breaks in DNA strands)
-chemical mutagens (eg. analogues of bases, base-modifying chemicals, intercalators causing frame shifts)
-biological mutagens (eg. tns)

Question 4

What is recombination?

Answer 4

Process of rearranging genetic info
-used in bact to repair DNA and shift off foreign DNA

Question 5

What are the types of recombination?

Answer 5

-homologous recombination (cross-over in similar DNA)
-non-homologous recombination (cross-over in dissimilar DNA)
-site-specific recombination (eg. att sites in λ phages)
-replicative recombination (tns)

Question 6

What is homologous recombination?

Answer 6

Recombination between very similar DNA seqs
-reqs 500bp of homology

Question 7

What is non-homologous recombination?

Answer 7

Recombination between dissimilar DNA seqs
-v rare

Question 8

What is site-specific recombination?

Answer 8

Recombination where a DNA seq is inserted at a specific site
eg. λ bacteriophage inserts its genome at att site in E.coli (insertion promoted by λ integrase)

Question 9

What is replicative recombination?

Answer 9

Recombination which generates a new copy of DNA segment
-transposons (using transposase)

Question 10

What is phenotypic selection?

Answer 10

Direct selection for mutant cells
-Only growth of mutated colonies able to grow in media (v. selective, kills WT)

Question 11

What is phenotypic screening?

Answer 11

All cells are screened for mutant