Unit 3--Lecture 17 (Genetics of Bacteria and Archaea)

Question 1

The Transforming Principle

Answer 1

Experiments of Griffith

Infections of mice with strains of Streptococcus

Rough and smooth colony types
—smooth: dead
—rough: healthy
—heat killed smooth: healthy
—heat killed smooth & rough: dead

Phenotype due to capsule protection

Avery, MacLeod, and McCarty extended Groffith’s results

DNA is the transforming material

Question 2

Competence

Answer 2

Competence: the ability to take up exogenous (naked) DNA

Some bacteria naturally competent

Question 3

Genetic Transformation

Answer 3

Competent cells (natural or artificial)

Naked DNA taken up, incorporated, and expressed

Question 4

Conjugation

Answer 4

Plasmid-directed transfer requires cell contact

Question 5

Hfr Strains

Answer 5

Integrated F factor

Conjugal transfer

Question 6

Generalized Transduction

Answer 6

Involves a lytic phage

Question 7

Specialized Transduction

Answer 7

Involves a lysogenic phage

Question 8

Defense Against Transferred DNA

Answer 8

Bacteria cut entering DNA at specific restriction sites

Bacteria add methyl groups to DNA
—-prevents restriction at those sites

Question 9

Telling Them Apart

Answer 9

Transformation: needs naked DNA
—-DNase will inhibit transformation

Conjugation: needs cell contact
—-0.2 um membranes will disrupt conjugation

Transduction: involves bacteriophage
—-unaffected by either condition

Question 10

Recombination

Answer 10

Entering DNA replaces chromosomal DNA
—-DNA enters via transformation, conjugation, transduction
—-also used to repair damaged DNA
—-requires specific recombination proteins
—-RecA
—-RecBCD
—-RuvAB

Question 11

Mutations

Answer 11

Mutation: mistake during replication or damage to DNA

Wrong bases incorporated
—-transition
—-transversion

Indels are bad

Mutations

Mutants

Mutagens

Question 12

Mutagens Cause Mutations

Answer 12

Electromagnetic radiation
—-UV light, gamma rays, x-rays

Question 13

Point Mutations

Answer 13

A single base is altered in the sequence

Silent mutation: TAT to TAC&raquo_space; Tyr to Tyr
Missense mutation: TAT to TTT&raquo_space; Tyr to Phe
Nonsense mutation: TAT to TAA&raquo_space; Tyr to Stop

Question 14

5-Bromouracil Mutagenesis

Answer 14

A = T
A = 5BU
G = 5BU
G = C

A becomes G

Transition

Question 15

Measuring Mutagen Strength

Answer 15

Ames test was created by Bruce Ames

Salmonella typhimurium used to test mutagens

His- mutant strain grown in the absence of histidine

Look for reversions to His+

Question 16

DNA Repair

Answer 16

Mismatch repair:
–mispaired base cut out of strand
–strand without methyl groups is newer
–assumes to be in error

Thymidine dimers:
–induced by UV
–cut out by UvrAB complex

Damaged bases:
–excised by specific enzymes
–excised by specific enzymes
–replaced by DNA Polymerase I

Recombinational repair:
–occurs just after strand has replicated
–undamaged strand is copied
–replaced damaged strand
–catalyzed by RecA recombinase

SOS repair:
–extensive DNA damage inactivates LexA
–activation of many repair genes
–rapid polymerization of DNA
–error-prone, but better than no repair