Bacterial Genome

Question 1

structure of cells and exchange of genetic information

Answer 1

Chromosome, transposon, plasmid
Conjugation: between two cells through pilus
Transformation: from the environment and incorporate into genome
Transduction: bacteriophages

Question 2

characteristics of DNA chr

Answer 2

haploid, circular dsDNA, nucleoid, loop domains (folded or supercoiled) - HU and DNA gyrose (super)

Question 3

replication of chr

Answer 3

oriC
bi-diretional
C time (40min)
independent of growth (division - 20min)
2 termination sites (ter)

Question 4

genome

Answer 4

unique and expressed 97%
protein 87%
no introns
less than 3% of repetitive sequences
conserved genes 60-80% - housekeeping (basic function)and MLST (evolutionary relationship)
dispersed genes- advantage, contigency loci (more mutations) enabling adaptation

Question 5

Repetitive Elements

Answer 5

Simple: = seq multiple times
Variable number of tandem repeats: dif sequences
Direct (same direction) and inverted dispersed repeats (opposite) : ends have repeats and middle has different longer sequence

Question 6

Plasmid

Answer 6

small, dsDNA, non essential but gives phenotype (selective advantage and pathogenicity)
vectors
autonomoud replication but use bacterial machinery - oriV - semi conservative and quick
self regultory: copy control regulator - replicon encodes own regulator - incompability when plasmids have same regulator
replicon and maintenance: host and division is stable (inheritance)

Question 7

transmission of plasmid

Answer 7

conjugation
- conjugative: large 50-100kb, unique origin of replicatio oriT and genes of transfer functions Tra+
ssDNA - pillus- dsDNA (1-2min)

• non conjugative (mobile): small, oriT but no Tra+, relaxation complex, transferred by co-resident conjugative plasmid

NOTE: episomes integrate chr (F factor - Hfr cell)

Question 8

transposable elements

Answer 8

move around, insert in chr, plasmid or phage, mutagenic, independent host recombination, can´t replicate alone in chr
- insertion sequences (IS) - short (1-2kb), has only the genes required to move (transposase) - two IR and transposase
- transposons: conservative (duplication) or copy and paste
composite: conservative - IS left (functional) – AbR – IS right (inactive)
complex: IR– transposase + resolvase–AbR(resistance)— IR

Question 9

Bacteriophages structure and genome

Answer 9

viruses that infect cells
CAPSID: protein that coats genome
structure: filamentous, head+tail, icosahedral

Genome: 5-250kb, ssDNA (circular), dsDNA or ssRNA, modified bases, overlapping genes

Question 10

Lifecycles of bacteriophages

Answer 10

Virulent (lytic) - infection causes death
1-adhere to bacteria (adsorption)
2- injects chr material
3- phage proteins synthesized and genetic material replicated (host chr degraded)
4- assembly of phages
5- lysis of cell and infection of other cells

Temperate (lysogeny): incorporate bacterial chr
1- adsorb to surface (receptor)
2- linear dsDNA injected
3- DNA circularizes by ligation of cohesive ss ends (cos)
4- recombination between phage and chr at attP and attB
5- phage integrated with phage genes OFF (prophage)

Prophage - phage genome carried passively and can loosse ability for reactivation
- excision of genome (WT phage)
- aberrant excision - phage+chr - phage with bacterial genes - specialised transducing phage