Bacterial Genetics

Question 1

Operon

Answer 1

• Sequence of DNA that contains multiple genes under the control of a single promoter and termination sequence. - Not in eukaryotic cells

Question 2

Polycistronic mRNA

Answer 2

• mRNA that has information for more than one gene (or protein product)

Question 3

Antigenic variation

Answer 3

• Changes in the composition or structure of a molecule

Question 4

Phase variation

Answer 4

• The turning “on” or “off” of the expression of a molecule

Question 5

Plasmids

Answer 5

• Small (1.5-120 kbp) circular supercoiled DNA - 1-5 copies/cell, large plasmids; 10-20 copies/cell, small plasmids - Replicate independently of the chromosome; inherited by daughter cells - Conjugative plasmids encode transfer enzymes, and sex pili for transfer to other cells (can support transfer of non-conjugative plasmids) - Can carry genes that confer phenotypic advantages to bacteria

Question 6

Plasmids clinical significance

Answer 6

• Conjugative plasmids may carry genes that provide resistance to antibiotics (R-plasmids) or make proteins that act as toxins or other pathogenic factors - R-plasmids may carry resistance to multiple antibiotics - Use of antibiotics has applied a strong selective pressure for bacteria that can resist them

Question 7

Bacteriophage structure and function

Answer 7

• Viruses that infect bacteria *specific, used to subtype bacteria (phage typing) - Structure *protein capsid that houses genome *may have base and tail *no membrane envelop - Genome *DNA or RNA *single or double stranded *linear or circular

Question 8

Bacteriophage life cycles

Answer 8

• Lytic (Virulent) *after binding have rapid replication: 20min from infection to lysis > leads to cell death and production of new (progeny) - Lysogenic (Temperate) *infection leads to cell lysis, or integration of phage DNA into the chromosome or the formation of a plasmid (prophage) *prophage conversion may increase the virulence of a bacterium (e.g. diptheria toxin is encoded on a prophage)

Question 9

Transposons

Answer 9

• Complex transposable elements that contain genes for transposition in addition to genes that encode for antibiotic resistance and other virulence properties - Insertion sequences are the smallest and most simple transposable elements - Transposable elements can move from one DNA site to another within a bacterial cell

Question 10

Genomic (Pathogenicity) Islands (PAI)

Answer 10

• Regions of DNA that contain mobile genetic sequences; encode for genes that enhance the virulence of a pathogen

Question 11

Transformation

Answer 11

• Transfer of “naked” DNA from a donor to a recipient
• Naturally competent bacteria are naturally capable of taking up exogenous DNA across their membranes w/o manipulation (e.g. Neisseria gonorrhoeae, Streptococcus pneumoniae)

Question 12

Conjugation

Answer 12

• Mediated by a conjugative plasmid (F plasmid, Fertility plasmid) that encodes for transfer (tra) genes and sex pili
• Requires intimate cell contact
• Plasmid transfers from F+ (male) to F- (female) cell. Result: 2 F+ cells
• Conjugative transfer of plasmids w/ resistance genes is an important cause of the spread of antibiotic resistance

Question 13

Transduction

Answer 13

• Transfer of genetic info from one bacterium to another by a bacteriphage
• Phage DNA incorporated into the bacterial chromosomes is called a prophage
• Process called lysogenic conversion; bacteria are called lysogenic bacteria

*e.g. only Corynebacterium diptheriae that have been lysogenized w/ the beta prophage produce diptheria toxin