Brewer - Bacterial Genetics

Question 1

What is the structure of bacterial DNA

Answer 1

Circular

Question 2

How does genome size reflect life style

Answer 2

The more genes something has the more capabilities it has. For instance E. coli has many more genes so it has the ability to live on just glucose. Mycoplasma on the other hand has a lot less genes and therefore needs a whole lot more to be present in the media.

Question 3

Replicons

Answer 3

Site for initiation of DNA synthesis within bacterial chromosomes and plasmids.

Question 4

How do you detect a plasmid?

Answer 4

You lose cells so that the plasmid espaces, but the chromosome stays inside of the cell. You then seperate the plasmids based on size on a gel electrophoresis. You ad ethidium bromide to make it fluoresce.
- If all of the brightness is concentrated in one area then it is one plasmid. If it is in different areas then it is many different plasmids.

Question 5

What is a bacteriophage?

Answer 5

Viruses that inject their genomes into a bacterial cell and uses its machinery for its reproduction.

Question 6

What are the two types of bacteriophage?

Answer 6

Virulent - bacteriophages release progeny by lysis of cells

Temperate - bacteriophages insert genomes into bacterial chromosomes and replicate with it.

Question 7

Provirus/prophage

Answer 7

Integrated viral genome into the bacterial chromosome that we see in temperate bacteriophages

Question 8

Insertion sequence

Answer 8

Can move from one location of DNA to another.

• the only gene that is has is for transposase, which is the enzyme that allows it to move from one spot to another.
• have an inverted repeat on both ends

Question 9

Transposons

Answer 9

Resemble insertion sequences but contain other genes other than just transposase gene. Therefore it can move genes like the antibiotic-resistance genes.

Question 10

Pathogenicity Islands

Answer 10

Are basically just very large Transposons. Can contain 50-100 gees. May contain a whole set of virulence genes for a particular organism.

Question 11

Two modes of transposition

Answer 11

Cut and paste

Replicative

Question 12

How does replicative transposition work?

Answer 12

It fuses donor and recipient molecules and then resolves them.

Question 13

3 mechanisms of DNA transfer between bacterial cells

Answer 13

Transformation
Conjugation
Transduction

Question 14

Transformation

Answer 14

One cell will pick up DNA fragments from a dying or lysed cell.

Question 15

COnjugation

Answer 15

Plasmid DNA from a donor cell is transferred to a recipient through a conjugation bridge/pilli.

Question 16

How is it that chromosomal DNA can be transferred through conjugation?

Answer 16

The F plasmid can be incorporated into the chromosome and the a conjugation bridge will form. The chromosome then acts just like a plasmid. The issue though is that these bridges are transient and break shortly so only a smart part of the chromosomal DNA will make it to the recipient cell.

Question 17

Transduction

Answer 17

• When a virus enters a cell, it can incorporate bacterial DNA into the progeny, so when. The cell lysis and the virus spreads, it could be spreading bacterial DNA
• The virus DNA can also have a small part of bacterial DNA in it.

Question 18

Merozygote

Answer 18

Complete bacterial chromosome + partial DNA fragment from donor.

Question 19

Phase variations

Answer 19

When microbes continue to create new variants of the antigen to escape the immune system.
- with each wave of antibiotics, there can be one microbe that alters its antigen and stays alive to proliferate the net generation.

Question 20

Three mechanisms of phase variation

Answer 20

Inversion of a segment of DNA
Recombination between expressed and silent genes
Shuttering by polymerase during copying of a repeat

Question 21

How does salmonella do phase variation?

Answer 21

It has two genes for its flagella, H1 and H2. Only one is expressed at a given time.
- The enzyme, hin, recognizes two inverted repeats and then inverts the DNA between the repeats.

Question 22

How does phase variation happen in Neisseria?

Answer 22

There is recombination betwen the silent copy and expressed copy of the piling genes so that a mosaic is created with alternating silent, expressed, etc.

Question 23

Phase variation in Neisseria outer membrane protein, PII

Answer 23

There is a variation in the number of CTCTT repeats. If there is a multiple of 3 CTCTT repeats then PII is made, otherwise it is not.