4 Bacterial Genetics

Question 1

Do bacteria have relatively large or small genomes?

Answer 1

Small

Question 2

Bacteria have ………………… DNA.
Bacteria have a …………………. genes.
Bacteria …….. introns.

Answer 2

Very little redundant DNA
Couple of thousand genes
Bacteria lack introns

Question 3

Because bacteria are small it means they can what?

Answer 3

Respond quickly to environmental changes

Question 4

What are bacteria able to do with their genes?

Answer 4

Quickly switch on when needed and switch off when not needed (upregulation and downregulation)

Question 5

What must gene expression be?

Answer 5

Tightly regulated

Question 6

What factors play a role in the gene expression process? And what do they do?

Answer 6

Sigma factors and cAMP - ensure proper transcription takes place in terms of starting and finishing points

Question 7

What are operons?

Answer 7

Genes with similar roles, or those which interact and work together under the same control

Question 8

Explain replica plates.

Answer 8

Replica plates are used to detect changes in bacteria.
Colonies grow on the original plate. Place a cloth (cheesecloth) over a block of wood which is almost the same size as the agar plate. Touch the plate gently with the cloth and transfer this imprint of colonies to fresh media (complete and minimal) and incubate.

By comparing the new plate with the original plate, look for colonies on the old plate which arent on the new plate, this is an indication of mutant colonies

Question 9

Explain the Ames test.

Answer 9

Using bacteria to check for mutagens

Bacteria is added to the plate, the suspected mutagen is added and plate is incubated. If the chemical is a mutagen then many colonies will form, if not a mutagen, fewer colonies will form

Question 10

How many chromosomes can DNA have?

Answer 10

One but they can have other forms of DNA present

Question 11

Where are most of the essential genes located?

Answer 11

On the bacterial chromosome (single copy)

Question 12

What do plasmids contain?

Answer 12

Non-essential (luxury) genes - can be multiple copies

This includes for antibiotic resistance, conjugation and virulence

Question 13

What are transposons and insertion sequences able to do?

Answer 13

Move from one position in the genome to another

Question 14

What happens if a transposon inserts in the middle of a gene? And what is it good for?

Answer 14

Then it will lose its function.

Good for genetic analysis

Question 15

Explain Transformation.

Answer 15

Bacterial chromosome from a lysed cell breaks up and is then taken up by a recipient cell

Question 16

Give an example of some genera/species that conjugation takes place in.

Answer 16

Bacillus and Streptococcus

Question 17

What does the cell need to be in order for transformation to occur?

Answer 17

Competent cell

Question 18

How can cells become artificially competent?

Answer 18

Changes to the bacteria cell wall are required. Using the correct growth medium at the correct stage of growth, the DNA can then be transformed into the cells

Question 19

What often happens to transformed DNA?

Answer 19

DNA will be destroyed by nucleases produced by the recipient cell

Question 20

What is required for the DNA to be incorporated into the bacterial chromosome?

Answer 20

Requires the enzyme recA

Question 21

Do all bacterial cells contain plasmids?

Answer 21

No

Question 22

What does conjugation require?

Answer 22

Cell to cell contact (normally the same species)

Question 23

What does conjugation entail?

Answer 23

Plasmids being passed from one bacterium to another

Question 24

How is contact initiated?

Answer 24

The pilus on the donor

Question 25

Is the transfer of DNA is unidirectional or multidirectional?

Answer 25

Unidirectional - donor to recipient

Question 26

Explain conjugation.

Answer 26

Pilus of donor attaches to recipient. It then disassembles drawing the recipient closer. Once they are physically toughing then their cell walls and cytoplasmic membranes fuse allowing a pore to develop and forming a conjugation bridge. DNA moves through this bridge from the donor to the recipient (only one strand is transferred).

Question 27

What happens to the DNA once it enters the recipient cell?

Answer 27

Recipient can replicate the ssDNA to become dsDNA. Now DNA is the same in both cells

Question 28

What can conjugation also involve?

Answer 28

Extra DNA being transferred (not restricted to plasma) Also presents an opportunity to pass on chromosomal DNA

Question 29

What are viruses in bacteria also referred to?

Answer 29

Bacteriophages (phages)

Question 30

How do viruses kill the cell? And how is this seen?

Answer 30

From a central point outwards and can be seen as plaques

Question 31

How are phages produced (think of the graph)?

Answer 31

Produces as a series of phases. Graph goes lag (latent), burst, latent, burst, etc.

Question 32

What does transduction entail?

Answer 32

A process by which bacterial viruses or phages infect bacteria

Question 33

What does transduction involve?

Answer 33

A phage which has come out of a donor cell which has probably been killed will find a new host. It attaches to the recipient and injects its DNA into the cell.

Question 34

Can transduction contain errors?

Answer 34

Yes

Question 35

How is DNA packaged into phages?

Answer 35

Some phages can package based on size of fragment in the core of the body of the phage

Question 36

What can packaged DNA sometimes contain?

Answer 36

Might contain DNA which should not have been included and so can act as a means of transferring DNA from one cell to another

Question 37

What can sometimes happen to the DNA from the phage?

Answer 37

It can become integrated into the bacterial chromosome

Question 38

What happens when the DNA from the phage becomes integrated into the bacterial chromosome?

Answer 38

The cell becomes resistant to further infection by that phage

Question 39

What is the stage called where the cell becomes resistant to further infection by the phage?

Answer 39

Prophage stage

Question 40

How long can a phage exist in the prophage stage?

Answer 40

Several generations

Question 41

What happens to the phage following the prophage stage? And why is this a good thing?

Answer 41

Excites itself again to become lytic Good way to avoid competing with other phages (by waiting until the time for infection is more suitable