October 14 Flashcards
Double Helix
size expressed as base pairs
kilo or mega base pairs
Kbp = 1000
Mbp =1 000 000
Bacterial DNA
Supercoiling
Found in chromosomes and plasmids
Supercoiling
No histones
Positive and negative supercoiling
negative: “underwound” most common
Positive: “overwound”
DNA gyrase
DNA Gyrase
Special topoisomerase responsible for supercoiling
Plasmids
- extra-chromosomal
- survival advantage
- most are circular
- most are double stranded
- replicate independantly (semi-autonomous, relies on enzymes coded for in chromosomal DNA)
Types of Plasmids
- Resistance plasmids
- Virulence plasmids
- Bacteriosins
Resistance Plasmids
Confer resistance to antibiotics and antimicrobials
Virulence plasmids
Allows to be pathogenic by:
- allows for attachment and colonization of tissue via fimbrae and capsule
- Produces toxins and enzymes that damage host tissue
*Pathogenic E. coli colonization factor antigen allows for attachment to intestinal cells
Bacteriosins
Kill other bacteria, more specific than antibiotics
Form channels in cell membrane, no longer selectively permeable causes cell death
Nucleases- destroy competitor nucleic acids
Niacin A: made by lactic acid bacteria, inhibits G+ growth
How do bacterial chromosomes replicate?
Bidirection replication because circular
Two replication forks leave to theta structure
Begins at orgin of replication, ends at terminus of replication
PCR
Polymerase Chain Reaction
Uses DNA pol, artificial primers start synthesis, amplifies target (up to 1000bp) from template.
- Denature DNA template by heating
- DNA primers present in excess, flank target DNA
- DNA pol extends primers
- Heat again (seperation of strands)
- Cool to allow primers to attach
- Repeat
What DNA pol is used in PCR?
- E. coli DNA Pol III, denatured and had to be replaced each cycle
- Thermus aquaticus: TAQ
- Pyrococcus furiosis: Pfu pol
