Genetic Transfer- Bacteria

Question 1

True or false: all bacteria only have circular DNA?

Answer 1

False, some bacteria can have circular, linear or linear and circular DNA. Some bacteria have more than one chromosome.

Question 2

What is the typical size of a plasmid?

Answer 2

1Kb-1Mb

Question 3

What is required for DNA incorporated into a cell to survive?

Answer 3

It must be able to replicate independently (encode for specific proteins e.g. integrases, recombinases) or be incorporated into the cell’s chromosome (requires some level of DNA similarity/homology).

Question 4

What is required for a cells to be able to undergo conjugation? Do they have to be encoded on the plasmid only?

Answer 4

• DNA that encodes for a sex pilus
• Express proteins required for DNA transfer
• DNA with a region that can begin transfer (origin of transfer oriT).
  No, they can be encoded on the bacterial chromosome.

Question 5

How large can a piece of chromosomal DNA be to undergo generalised transduction?

Question 6

What are the four ways in which DNA can be introduced into a bacterial cell? I.e. how can transfection be achieved?

Answer 6

• Modification of cell membrane through electroporation or chemical treatment
• Addition of DNA in liposomes
• Physical introduction into nucleus using gene gun (useful for plant cells with cellulose cell wall)
• Viral transduction (gene therapy)

Question 7

Approximately how many genes does human DNA have? How many bp?

Answer 7

Approximately 20 000

3 300 000 000

Question 8

What is the importance of histomes?

Answer 8

Histomes are basic proteins that are highly positively charged. They neutralise the negatively charged DNA, allowing compression of it. Otherwise, DNA compression would not be possible to the same extent.

Question 9

How much of the human genome codes for proteins?

Answer 9

2%

Question 10

How do new genes arise?

Answer 10

Replication errors, recombination during meiosis.

Duplication of genes and different development of those genes.

Question 11

What is the difference between mini satellite DNA and micro satellite DNA?

Answer 11

Micro satellite DNA is 1-14 bp repeated in tandem up to 10 times. Can be within genes. Changes in repeat number can cause disease.
Mini satellite DNA is 14-500 bp in length, repeated in tandem up to 100s of times. Highly specific and so used for finger printing.

Question 12

Can prokaryotes have RNA based transposable elements?

Answer 12

No, they can only be DNA based in prokaryotes.

Question 13

What are the two mechanisms for transposon movement?

Answer 13

Conservative- moves to different area

Replicative- duplicated and duplicate moves elsewhere.

Question 14

What enzymes are required for a retrovirus to be incorporated into a eukaryotic organism’s genome?

Answer 14

• Reverse transcriptase

- Integrase/transposase

Question 15

What are the types of transposable elements in prokaryotes and eukaryotes?

Answer 15

Prokaryotes:
- Insertion sequences
- Transposons
- Bacteriophages 
Eukaryotes:
- Transposons
- Retro-viruses
- Retro-transposons.

Question 16

Difference between lytic and lysogenic cycles of bacteriophages?

Answer 16

Lytic- produces several copies of self, the cells lyses and bacteriophage copies released.
Lysogenic- inserted into bacterial chromosome and replicates with it. Can eventually leave the chromosome.

Question 17

What are some examples of RNA viruses?

Answer 17

Influenza, HIV, poliovirus

Question 18

What are some DNA viruses?

Answer 18

Smallpox, T4 bacteriophage.

Question 19

What are some examples of bacteria with a single circular chromosome?

Answer 19

E. coli, Haemophilus influenzae, Neisseria meningitidis, Pseudomonas aeruginosa

Question 20

What are some examples of bacteria with two circular chromosomes?

Answer 20

Vibrio cholerae, Burkholderia pseudomallei, Leptospira borgpetersenii

Question 21

What is an example of bacteria with linear chromosomes?

Answer 21

Borrelia burgdorferi- Lyme disease

Question 22

What is an example of bacteria with a linear and a circular chromosome?

Answer 22

Agrobacterium tumefaciens

Question 23

What are transposons?

Answer 23

Insertion sequences that can move in and out of chromosome. These include:

• Insertion sequences
• Composite transposons
• Some bacteriophages.

Question 24

What is a plasmid copy number?

Answer 24

The average number of copies of a plasmid in a cell. 1-500.

Question 25

True or false; the number of plasmids in the offspring is the same as that in the parent bacteria following cell division?

Answer 25

True

Question 26

What are some functions that a plasmid encodes for?

Answer 26

Copy number control and replication
Resistance (antibiotics, heavy metals)
Virulence genes (toxin production, secretion systems)
Metabolic enzymes- exploit niches
Production of antimicrobials (bacteriocins) to eliminate competition
Mobility (conjugation) factors.

Question 27

Without its plasmids could Shigella cause disease?

Answer 27

No, its virulence factors are encoded on its 220-kb virulence plasmid.

Question 28

What genetic elements allow vertical genes transfer? Horizontal gene transfer?

Answer 28

Vertical: chromosomes, plasmids
Horizontal: transformation, conjugation, transduction.

Question 29

How can DNA be integrated into the host chromosome?

Answer 29

1. Encode for its own integration proteins0 integrases, recombinases.
2. Recombine into the chromosome by homologous recombination- requires some level of homology.

Question 30

What is generalised transduction?

Answer 30

Bacteriophage incorrectly packages bacterial DNA into the phage parcel.