Mid Genetics Ii

Front 1

What is the general idea of transduction?

Back 1

DNA is encapsulated in a virus particle. Transduction occurs because a phage infects a bacterial cell and then the phages are released and they carry with them their own DNA and some of the DNA of the bacteria they previously infected. They infect the recepient cell.

Front 2

What are the two transduction pathways?

Back 2

-Lytic
-Lysogenic

Front 3

Describe generalized transduction

Back 3

A DNA fragment is transferred from one bacterium to another by a lytic bacteriophage that is now carrying donor bacterial DNA due to an error in maturation during the lytic life cycle

Front 4

Describe specialized transduction

Back 4

A DNA fragment is transferred from one bacterium to another by a temperate bacteriophage that is now carrying donor bacterial DNA due to an error in spontaneous induction during the lysogenic life cycle.

Front 5

What are the steps of generalized transduction?

Back 5

1. A lytic bacteriophage adsorbs to a susceptible bacterium
2. The bacteriophage genome enters the bacterium. The genome directs the bacterium's metabolic machinery to manufacture bacteriophage components and enzymes.
3. Occasionally, a bacteriophage head or capsid assembles around a fragment of donor bacterium's nucleoid or around a plasmid instead of a phage genome by mistake.
4. The bacteriophages are released
5. The bacteriophage carrying the donor bacterium's DNA adsorbs to a recipient bacterium
6. The bacteriophage inserts the donor bacterium's DNA it is carrying into the recipient bacterium
7. The donor bacterium's DNA is exchanged for some of the recipient's DNA

Front 6

What are the steps of specialized transduction

Back 6

1. A temperate bacteriophage adsorbs to a susceptible bacterium and injects its genome
2. The bacteriophage inserts its genome into the bacterium's nucleoid to become a phophage.
3. Occasionally during spontaneous induction, a small piece of the donor bacterium's DNA is picked up as part of the phage's genome in place of some of the phage DNA which remains in the bacterium's nucleoid.
4. As the bacteriophage replicated, the segment of bacterial DNA replicates as part of the phage's genome. Every phage now carries that segment of bacterial DNA.
5. The bacteriphage adsorbs to a recipient bacterium and injects it genome.
6. The bacteriophage genome carrying the donor bacterial DNA inserts into the recipent bacterium's nucleiod.

Front 7

What is a sex pilus?

Back 7

Sex pilus is a protein structure that creates a bridge between two cells. It is a tube that transfers DNA from cell to cell.

Front 8

What is bacterial conjugation?

Back 8

Genetic recombination in which there is a transfer of DNA from a living donor bacterium to a recipient bacterium. Often involves a sex pilus.

Front 9

Describe conjugation

Back 9

-Direct transfer of DNA from one strain to another
-Best studied in E. coli and approximately a third of freshly isolated E. coli has plasmids
-Conjugatin plasmids have been found in approximately 30 genera of bacteria, mostly graam-negative. Antibiotic-resistance plasmids RP4 and R68.45 can propagate and promote conjugation in virtually any gram-negative bacterium.
-Some gram-positive conjugate such as Streptococci, Staphylococcus, Streptomyces, Clostridium, and Bacillus

Front 10

What is F+ conjugation

Back 10

Genetic recombination in which there is a transfer of a large (95kb) plasmid F+ plasmid (coding only for a sex pilus) but not chromosomal DNA from a male donor bacterium to a female recipient bacterium. Involves a sex (conjugation) pilus. Other plasmids present in the cytoplasm of the bacterium, such as those coding for antibiotic resistance, may also be transferred during this process. F can be transferred from a E. coli to Salmonella, Shigella, and Proteus

Front 11

What are the steps of F+ conjugation?

Back 11

1. The F+ male has an F+ plasmid coding for a sex pilus and can serve as a genetic donor
2. The sex pilus adheres to an F- female (recipient). One strand of F+ plasmid breaks.
3. The sex pilus retracts and a bridge is created between the two bacteria. One strand of the F+ plasmid enters the recipient bacterium.
4. Both bacteria make a complementary strand of the F+ plasmid and both are now F+ males capable of producing a sex pilus. There was no transfer of donor chromosomal DNA although other plasmids the donor bacterium carries may also be transfered during F+ conjugation.

Front 12

What are R plasmids?

Back 12

R-plasmids are F+ plasmids that contain antibiotic resistance elements. These are transmitted effectively and quickly through populations. These plasmids have the genes important for transfer, but also the genes that encode for antibiotic resistance.

Front 13

What are the steps of R-plasmid conjugation?

Back 13

1. The bacterium with an R-plasmid is multiple antibiotic resistant and can produce a sex pilus
2. The sex pilus adheres to an F- female (recipient). One strand of the R-plasmid breaks
3. The sex pilus retracts and a bridge is created between the two bacteria. One strand of the R-plasmid enters the recipient bacterium.
4. Both bacteria make a complementary strand of the R-plasmid and both are now multiple antibiotic resistant and capable of producing a sex pilus.

Front 14

What are transposons?

Back 14

Transposons are plasmids that have inserted themselves into the chromosome of the bacteria. It can be silent for multiple generations. At somepoint when conditions are right the transposon excises.

Front 15

Describe conjugative transposons

Back 15

-Carry genes flanked on both sides by IS elements
-IS elements supply transposase and ITR recognition signals.

Front 16

What is pXO1?

Back 16

A bacterial plasmid that encodes the anthrax toxin genes

Front 17

What is pXO2?

Back 17

A bacterial plasmid that encodes the anthrax capsule genes