6.3.3 Bacteria Genetics

Question 1

What is bacterial genome?

Answer 1

all genetic info in the cell

bacterial chromosome

plasmids

Question 2

Describe bacterial chromosome

Answer 2

circular

haploid

supercoiling

Question 3

Describe plasmids

Answer 3

not in all bacteria

circular, 1-300 kbp

self-replicating, don’t need chromosomal machinery for that

non-essential genes

one bacterium may have more than one type of plasmid coding for different genes

Question 4

What are transposons?

Answer 4

elements of DNA that cannot self-replicate

contain insertion sequences which allow them to ‘jump’ into another plasmid or even into the chromosome (to allow replication)

enhance genetic diversity and evolution by causing deletions and genetic rearrangement

usually associated with antimicrobial resistance

Question 5

What is Restriction and Modification system?

Answer 5

Restriction endonuclease cuts foreign DNA on recognition site

Methylase / methyltransferase methylates sequences in self DNA so they’re protected from endonuclease action

Question 6

no sexual reproduction in bacteria - so how does evolution occur?

Answer 6

spontaneous mutation of existing genes

acquisition of new genetic material via horizontal gene transfer

Question 7

What is horizontal gene transfer?

Answer 7

Extra-chromosomal acquisition of new genes

transformation - uptake of ‘naked DNA’ (from any origin into any bacterial species)

transduction - bacteriophage-mediated (species-specific)

conjugation - cell-to-cell contact via pili (species-specific)

Question 8

What is spontaneous mutation? Effects?

Answer 8

heritable change in DNA sequence that can (but doesn’t have to) lead to a change in phenotype

mutagens are chemical, physical or biological agents that increase the mutation rate

Question 9

Describe bacterial transformation

Answer 9

uptake of ‘naked DNA’

DNA fragment crossing bacterial cell membrane

Question 10

Explain the process of bacterial transduction

Answer 10

bacteriophage-mediated exchange

phage injects DNA to the cells, uses cell machinery to replicate

when too many new phages in a bacterium it will lyse releasing the phages to infect next cells

phages with bacterial DNA will transmit it to different cells (normally closely related bacteria)

Question 11

Explain conjugation

Answer 11

cell-to-cell contact via pili

pili can be species and lineage-specific so usually two cells of the same type