microbial genetics

Question 1

prokaryote chromosomes are

Answer 1

single, circular molecule of DNA

has a singly origin of replication

Question 2

plasmids are

Answer 2

smaller circular DNA molecules

replicate independently of chromosome

Question 3

phages are

Answer 3

viruses of bacteria

genetic material can be DNA or RNA

Question 4

what is vertical transmission

Answer 4

inheritance of DNA through cell division

transfer from mother to daughter cells

Question 5

what is horizontal transmission

Answer 5

transfer of DNA between cells without cell division

can occur between unreleated cells

sometimes described as ‘bacterial sex’

Question 6

conjugation

Answer 6

donor cell attaches to a recipient cell with its pilus, drawing the cells together

the cells contact with one another

one strand of plasmid DNA transfers to the recipient

recipient synthesizes a complementary strand to become an f+ cell

the donor synsthesizes a complementary strand, restoring its complete plasmid

Question 7

Hfr strains

Answer 7

F plasmid DNA is incorporated into bacterial chromosome by recombination between plasmid and chromosome

during conjugation a single-stranded copy of chromosome fragment is produced

and transfered to recpipent cell

becoming double stranded

crosses over with chromosome of recipient cell, forming recombinant chromosome

Question 8

entry mapping

Answer 8

interrupted mating experiments- mix Hfr and recipient strains, separate mating cell pairs after time, kill donor cells, test recipient for presence of donor alleles

donor alleles appear in recipient cells after a specific time period, in a specific order

f plasmid DNA is always transferred last and can insert at different points on the circular chromosome

Question 9

recombination

Answer 9

recombination at conjugation occurs between circular chromosome and linear fragment

single crossover would break circle

double crossover produced intact circule and linear fragment

Question 10

f ‘ plasmid

Answer 10

exits Hfr chromosome

can incorporate part of the bacterial chromosome

transferred to new cell by conjugation

generates partial diploid allows studies of dominance

Question 11

R plasmids

Answer 11

carry alleles for drug resistance

can spread rapidly through bacterial population by conjugation

Question 12

transformation

Answer 12

DNA fragments in the environment enter bacterial cell through cell wall and plasma membrane
and is incorporated into chromosome by double recombinatino

source of DNA- dead cells, living cells of the same or different species

Question 13

phages doing stuff

Answer 13

DNA or RNA chromosome- surrounded by protein coat

attaches to bacterium- injects its DNA into the cytoplasm, turns off synthesis of bacterial proteins, turns off synthesis of phage proteins

lysis- bacterial cell wall is broken open, new phages are released to infect new bacteria

Question 14

what are phage crosses

Answer 14

where several phages infect the same cell

recombination can occur

Question 15

generalised transduction

Answer 15

phage accidentally incorporates fragment of bacterial chromosome, injected inot a new bacterial cell

genes which are close together are more likely to occur on the same DNA fragment

Question 16

lysogeny

Answer 16

temperate phage occurpies its host without killing it

transmitted vertically as a plasmid, intergrated into host DNA as a prophage

Question 17

specialised transduction

Answer 17

prophage exists bacterial chromosome by crossing over between flanking regions

can incorporate part of the bacterial chromosome, transferred to new cell, incorporate into new bacterial chromosome