Microbial Genetics

Question 1

Mutation

Answer 1

A heritable change in genetic material

Question 2

Mutagen

Answer 2

Agent that causes mutations (chemicals, radiation)

Question 3

Spontaneous Mutation

Answer 3

Mutation the occurs in the absence of a mutagen (1 in 10^-6 per replicated gene)

Question 4

Base Substitution Mutation

Answer 4

Change in one base pair

Question 5

Silent Mutation

Answer 5

No change in amino acid sequence (No phenotypic change)

Question 6

Missense Mutation

Answer 6

Change in an amino acid (Possible phenotypic change)

Question 7

Nonsense Mutation

Answer 7

Introduces new stop codon with truncated protein (Likely phenotypic change)

Question 8

Frameshift Mutation

Answer 8

Insertion or deletion of nucleotide pairs, changing reading frame and amino acid sequence (Likely phenotypic change)

Question 9

Recombination is important because…

Answer 9

…it physically exchanges DNA between genetic elements, creating new combinations of genes without mutation (genetic diversity)

Question 10

Transformation

Answer 10

Genetic transfer process in which free DNA is incorporated into a recipient cell

Question 11

Cells can be competent using…

Answer 11

…calcium chloride or electroporation

Question 12

Competence occurs due to…

Answer 12

quorum sensing of competence factors, which leads to the synthesis of transformasome, which grabs a single strand of extracellular DNA (and degrades the other)

Question 13

Transformation Process

Answer 13

1. DNA is taken up (fragment or plasmid)
2. DNA is integrated by nonreciprocal recombination (fragment)
3. If successful, fragment is integrated into chromosome; if unsuccessful, fragment is degraded

Question 14

Plasmid Replication (2)

Answer 14

• Replicate independently

- Replicate normally or by rolling circle

Question 15

Plasmids that encode enzymes for catabolism of unusual compounds

Answer 15

Dissimilation Plasmids

Question 16

Plasmids that encode antibiotic resistance

Answer 16

R Plasmids

Question 17

Plasmids that encode toxin production

Answer 17

Virulence Plasmids

Question 18

Plasmids that carry genes for sex pili and plasmid transfer

Answer 18

Conjugative or F Plasmids

Question 19

Conjugation

Answer 19

Transfer of genetic material from direct cell contact

Question 20

Conjugation Process

Answer 20

1. Donor Cell (F+) makes pilus and attaches to receptors on recipient cell
2. Contraction of pilus draws the cells together to form a relaxosome bridge
3. The F plasmid is nicked at oriT and the 5’ begins transfer through the bridge
4. The remaining strand is replicated and the donated strand circularizes and replicates in the recipient cell

Question 21

A donor Hfr cell transfers chromosomal genes but…

Answer 21

…leaves the recipient as F- (if it began as F-)

Question 22

Transduction

Answer 22

The transfer of bacterial genes by viruses

Question 23

Generalized Transduction Process (4)

Answer 23

1. Chromosome DNA fragments are packaged in a capsid, creating a transducing particle
2. Once released, the phage can infect another host cell
3. Infection will introduce the original DNA into the new cell
4. Occurs at low frequency and only during lytic cycle

Question 24

Specialized Transduction Process (3)

Answer 24

1. Integrated viral DNA excises from chromosome and grabs nearby gene
2. Phage infects new host carrying viral DNA and bacterial gene with it
3. Occurs only during lysogenic cycle

Question 25

Mobile Genetic Elements (MGEs)

Answer 25

Segments of DNA that move as units to new locations within DNA molecules

Question 26

Insertion Sequences

Answer 26

Short pieces of mobile DNA (~1kbp) with short inverted repeats at ends; encodes transposase

Question 27

Transposons

Answer 27

Larger mobile DNA (up to 40kbp) that encode trasposase and other genes