Microbial genetics

Question 1

What is a plasmid?

Answer 1

1. Small circular DNA molecule separate from bacterial chromosome2. Replicated and transferred to daughter cells3. May integrate into chromosome (episome)

Question 2

What types of genes can be carried on a plasmid?

Answer 2

1. R factor2. Toxin3. Bacteriocins4. Virulence determinants

Question 3

Vertical gene transfer

Answer 3

Genes passed via replication to progeny

Question 4

Horizontal gene transfer

Answer 4

Genes passed via1. Transformation2. Conjugation3. Transduction

Question 5

Is new DNA acquired during bacterial cell division?

Answer 5

No

Question 6

How is evolution of new traits conferred in bacteria?

Answer 6

DNA polymerase error rate

Question 7

What is the importance of horizontal gene transfer?

Answer 7

1. A way for bacteria to get around slow evolution rate2. Bacteria can become antibiotic resistant and produce new virulence factors more quickly than compared to vertical

Question 8

Homologous recombination

Answer 8

Exchange of DNA between two DNA molecules based on homology

Question 9

What is the result of homologous recombination?

Answer 9

DNA incorporated into the chromosome are passed to daughter cells / become a permanent part of the genome

Question 10

What are the steps of homologous recombination in bacteria?

Answer 10

1. Linear DNA acquired somehow2. RecA-mediated gene exchange at a homologous region 3. Linear DNA degraded by exonucleases

Question 11

What is transformation?

Answer 11

1. Uptake of free DNA from environment2. DNA is released into environment3. DNA is actively imported into the bacterial cell4. Homologous recombination can occur if DNA sequence is similar to portion of chromosome

Question 12

What is the purpose of transformation?

Answer 12

Allows bacteria to gain new traits quickly

Question 13

What is conjugation?

Answer 13

DNA transfer directly from one bacterial cell to anther through cell contact

Question 14

What is the purpose of conjugation?

Answer 14

Acquire new DNA from another viable bacterium

Question 15

What is the F factor?

Answer 15

1. Fertility factor2. Carries genes, tra operon (encodes sex pillus)3. OriT is where single strand break occurs for transfer

Question 16

What is required to pass on newly acquired DNA to progeny during conjugation?

Answer 16

Homologous recombination

Question 17

What are the characteristics of F+ x F- conjugation?

Answer 17

1. Transfer is unidirectional2. F- undergoes a sex change to F+3. Only a single strand is transferred4. No bacterial genes are transferred

Question 18

What are the characteristics of Hfr x F- conjugation?

Answer 18

1. Sex pillus forms2. When DNA is transferred from oriT, it actually brings in chromosomal DNA3. Partial genetic material is transferred4. No sex change occurs

Question 19

What is transduction?

Answer 19

Transfer of bacterial DNA via a bacteriophage

Question 20

What is generalized transduction?

Answer 20

1. Occurs with lytic phage2. A lytic phage incorporates bacterial chromosomal DNA into its phage head3. When the phage infects another bacterium the DNA can be incorporated into its chromosome via homologous recombination

Question 21

Generalized transduction occurs with what type of bacteriophage?

Answer 21

Lytic phage

Question 22

What is specialized transduction?

Answer 22

1. Occurs with lysogenic phage2. Incorporates as a prophage next to a gene3. A damaging event leads to conversion to a lytic lifecycle4. Upon excision from the genome, a small portion of the chromosome directly adjacent to where the phage was integrated is packaged into a phage head

Question 23

During what type of DNA transfer is homologous recombination NOT required?

Answer 23

F- / F+ conjugation

Question 24

What are the three categories for antibiotic resistance?

Answer 24

1. Intrinsic2. Chromosome mediated3. Plasmid mediated

Question 25

What are characteristics of intrinsic antibiotic resistance?

Answer 25

1. Non transferable (horizontally) between bacteria2. Not increasing among bacteria populations3. Example - lack of a bacterial target

Question 26

What are characteristics of chromosome mediated antibiotic resistance?

Answer 26

1. Chromosomal genes encode resistance2. Arise through random mutation during replication 3. Arise through acquisition of DNA via horizontal gene transfer and homologous recombination4. Examples - ribosomal proteins, PBPs, gyrase

Question 27

What are characteristics of plasmid mediated antibiotic resistance?

Answer 27

1. Genes encoding antibiotic resistance located on a plasmid2. Commonly plasmids carry genes that encode proteins that degrade or modify an antibiotic or an efflux pump to pump antibiotic out of cell

Question 28

What is the R factor?

Answer 28

1. Conjugated plasmid 2. Encodes a tra gene and a resistance determinant 3. Has an Rtf (resistance transfer factor) - resistance machinery

Question 29

What are transposons?

Answer 29

1. Mobile DNA elements that can transfer themselves or a copy from one DNA molecule to another 2. Present in both eukaryotic and bacterial cells, and viruses3. Contain:a) Indirect repeat sequences on each endb) A single gene for transposasec) A single or multiple antibiotic resistance genes

Question 30

How can multi drug resistance plasmids be constructed and passed between bacterial species?

Answer 30

Transposons can jump between two chromosomes, between plasmids, or between one another

Question 31

What are integrons?

Answer 31

1. Diverse group of genetic elements that a) Encode a site specific recombination systemb) Capture antibiotic resistance gene cassettesc) Coordinately express them under control of integron promoter2. Associated with large mobile genetic elements like plasmids or transposons3. Very important in rapid multi-drug resistance

Question 32

What are pathogenicity islands?

Answer 32

1. Region of a bacterial chromosome acquired through horizontal gene transfer2. Carry coordinately regulated virulence genes surrounded by insertion sequences 3. Another way to gain different traits quickly