bacteria genetic

chromosome

• shape

• how many base pairs long

Circular Haploid

0.8 - 4x106 base pairs long (4000 kbp)

One copy to each daughter cell

All essential genes for life in chromosome

length

E. coli genome = 4.6x106 bps = 1mm

E. coli cell = 1µm long = 1000 times shorter than genome BUT genome takes up 10% of cell volume

supercoiling and unwiding

DNA topoisomerase/gyrase enzymes

plasmids

• many bacteria

• circular 1-300kbp

• self replicating 1-50 copies./ cell

• oe bactierum may have more than one

• non essential genes

  • pathogenicity

  • AMR

  • self transmissibility

transposon

• do they self replicate

• what do they contain

• where do they jump between

• what do tey cause

• elements of DNA which cannot self replicate

• contain insertion sequences whic allow then to jumo into new parts of hte genome (transposition)- stcky end

• this can include jumping beteen plasmid and chromosme or different plasmid

• by causing deletions and genetic rearragement they enhancegenetic diversty and evolution

• usually associated with antimicrobial ressitance

• ability to move between chromosmes and plasmids increases spread of AMR

restriction and modification

• what are the 3 parts

• what is the 2 enzyme system

primitive immune system- recognise and distinguish incoming fooregin na from self

ubiquitous among prokaryotes

restriction- cutting (site specific endonuclease actiivty)

modifcation- protection (site specific dna methylase act)

defence mechanisms used to prevent infection by foregin DNA

• 2 enzyme sstem- restriction endonuclease and methylase (or methyltransferase)

how can change come about by

• phenotypic adaptation: metabolic adjustment in whole pop eg biofilm formation

• genetic change

how can bacteria genotype vary

• through spontaenous mutation of existing genes or acquisition of new genetic material via horizontal gene transfer

• heritablechange in a dna sequence can lead to a change in phenotype

• therefore a mutant differs in genotype from its parents but not necessarily phenotpe

• eg point mutations, large duplication, deletion

how can mutation occur

• most commonly spontaenous

• mutagen

  • chemical, physical or biological agent that increase mutation rate

horitzontal gene transfer

• extra chromosomal acquisitoin of new genes

  • transformaiton- uptake of naked dna- DNA from any origin into any bacterial species (most of the type prokaryotic as eukaryotic wouldnt pose as an advantage but could be from any bacteria eg shigella toxin to e. coli)

  • transduction- bacteriophage mediated

  • conjugation- cell to cell cotnact via pili

• transduction and conjugation are species specific, potentially lineage specific

trasnformation

• uptake of naked dna. eg released from a lysed cell

• dna can pass through bacterial cell envelope - can use shocking in lab to increase rate of uptake

• become part of genome

• if are circular they are self replicable if they are transposons they must integrate

transduction

• bacteriophage mediated exchange (viral type structure)

• pins and base plates, inject genetic material into cell.

• replicate

• reassemble in cell

• can mistakenly uptake bacterial dna

• cell lyses and can spread bacteria dna

• this can inject this into other cells

conjugation

• cell cell contact via pilli

• cell must be in direct contact

• plasmid can move- 2 cells can then have same plasmid

• species specific