Lecture 4 - Bacterial Gene Transfer

Question 1

Range of sizes of bacterial genomes

Answer 1

500 - over 4000 genes

Question 2

Can bacterial chromosomes be linear?

Answer 2

Yes

Question 3

Error rate of E. coli DNA replication

Answer 3

1 in 10 million - 1 in 100 million

Question 4

SNP

Answer 4

Single Nucleotide Polymorphism

Question 5

Codon bias

Answer 5

The ratio in a bacterial species of G-C nucleotides to A-T.

Normally balanced, but can be unequal.

Question 6

How can protein expression be efficient or inefficient?

Answer 6

Codon bias in a bacterium can bias towards certain codons of one amino acid.

EG: Mycobacterium has ~75% G-C.
Phe can either be TTT or TTC. The TTC codon is more efficient, as there are more tRNAs with a C than with a T.

Question 7

Is most bacterial DNA coding or non-coding?

Answer 7

Coding

Question 8

Example of mutations controlling gene expression

Answer 8

bvgA, bvgS genes in B Pertussis
Contains a sequence of repeated C.
Adding or omitting a C results in a STOP codon.
This inactivates bvg.
Addition of mono-, di- or tetra- nucleotides restores function

Question 9

Example of a bacterium that uses internal DNA recombination

Answer 9

Neisseria gonnorrhoeae

Question 10

How do neisseria gonorrhoeae alter surface pili?
1)
2)
3)

Answer 10

1) pilS (silent) and pilE (expressed) genes exist.
2) pilS lacks a promotor region
3) Gene segment of pilS can be recombined into pilE, altering pilE pili.

Question 11

When do bacteria lose function of parts of their genomes?

Answer 11

When they host adapt

Question 12

How is chromosome location important for a gene?
1)
2)

Answer 12

1) When bacteria divide, DNA remains functional.
2) The closer a gene is to the origin of replication, the more time it spends as two copies of a gene while the chromosome divides

This is called ‘gene duplication.’

Question 13

How is Salmonella typhi more adapted to humans than Salmonella typhimurium?

Answer 13

Has more pseudogenes (parts of genome inactivated)

Question 14

How does a bacterium protect itself from it’s own restriction enzymes?

Answer 14

Particular methylation pattern on own genome

Question 15

Three types of horizontal gene transfer

Answer 15

Transformation
Conjugation
Transduction

Question 16

What is transformation?

Answer 16

Bacteria taking up genetic material from the environment

Question 17

What is conjugation?

Answer 17

Bacteria transferring genetic material between one another using a sex pilus and a mating bridge

Question 18

How do naturally competent bacteria ‘know’ which genetic material to pick up from the environment?

Answer 18

Species-specific DNA uptake sequences on genetic material

Question 19

Is E. coli naturally transformable?

Answer 19

No

Question 20

What is a transformasome?

Answer 20

An extracellular vesicle-like structure containing genetic material

Question 21

Example of a bacterium that uses transformasomes

Answer 21

Haemophilus influenzae

Question 22

What kind of genetic code is transferred across a mating bridge?

Answer 22

ssDNA

Question 23

Examples of genes which could be horizontally transferred

Answer 23

Resistance plasmids
Transposons
Pathogenicity Islands

Question 24

Name of cell giving DNA and cell receiving DNA in transformation

Answer 24

Donor cell and recipient cell.

Recipient cell progeny are called transformants

Question 25

Examples of barriers to transformation

Answer 25

Restriction enzymes
Membranes
DNA-degrading environment

Question 26

Experiment demonstrating transformation
1)
2)
3)
4)

Answer 26

By Fred Griffith, 1928
Used Streptococcus pneumoniae
1) Inject mice with capsulated bacteria, mice die.
2) Inject mice with uncapsulated bacteria, mice survive.
3) Inject mice with heat-killed capsulated bacteria, mice survive.
4) Inject mice with heat-killed capsulated bacteria and live uncapsulated bacteria, mice die

Question 27

On average, how many DNA uptake sequences are in a genome?

Answer 27

10 - 12 locations on genome

Question 28

Differences in DNA uptake proteins between G+ And G- bacteria

Answer 28

G+ DNA uptake proteins need to only traverse one membrane

G- need to be more sophisticated, as they need to traverse a double membrane

Question 29

Can conjugation occur between bacteria of different genera?

Answer 29

Yes

Question 30

Name of bacterium that receives ssDNA in conjugation

Answer 30

Transconjugant