viruses and bacteria genetics

Question 1

what makes bacteria valuable research objects

Answer 1

• small size
• rapids reproduction
• selective media that can easily identify the presence of an active allele
• simple physiology (monoploid)
• genetic variability

Question 2

bacteriophages

Answer 2

• bacterial viruses
  -reproduce by infecting bacterial cells

Question 3

colony

Answer 3

population that derives from a single bacterium, all have the same genotype

Question 4

dilution series

Answer 4

help pick out a single colony, easier to do when they are more spread out
- will isolate same species of bacteria that has genetic variation

Question 5

plaques

Answer 5

bacteriophages produce clearances on plates with dense bacterial cultures within hours of infection

Question 6

Bacteriophage T4

Answer 6

docs to surface of bacteria and injects its genetic material into the bacterium
- virus itself does not enter the cell
- protein coat (especially in virus head) envelopes genetic material
- goes through a lytic phase - lyses the cell to infect other cells

Question 7

Bacteriophage lambda

Answer 7

• may be lytic or lysogenic
• genome contains 48,502 base pairs and about 50 genes

Question 8

retrovirus

Answer 8

• has RNA genome
• less stable than DNA and more prone to degradation since it is single-stranded
• more adaptable because higher rate of mutations

Question 9

retrovirus cycle

Answer 9

• virus attaches to host cell at receptors in the membrane and viral core enters host cell
• RNA degrades and reverse transcriptase synthesizes second DNA strand
• viral DNA enters the nucleus and is integrated in host cell chromosome forming a provirus
• proviral DNA is transcribed to viral RNA which is exported to cytoplasm where it is translated and new material is assembled

Question 10

lytic cycle

Answer 10

• phage binds to the bacterium and its DNA enters host cell
• host DNA is digested
• phage DNA replicates
• host cell transcribes and translates phage DNA into proteins
• assembly of new phages is complete and are released to start the cycle again

Question 11

sensor proteins

Answer 11

stimulus that tells prophage from the lysogenic cycle to enter the lytic cycle
- can detect if bacteria is healthy and wants to infect them

Question 12

lysogenic cycle

Answer 12

• phage binds to the bacterium and its DNA enters the host cell
• phage DNA integrates into the bacterial chromosome (through crossing over) and becomes a prophage
• prophage is replicated as part of the bacterial chromosome
• the prophage may separate from the chromosome and the cell will enter the lytic cycle

Question 13

prophage

Answer 13

inactive phage that is dormant in the host genome

Question 14

Genomes of bacteria

Answer 14

• genomes are circular, called bacterial chromosomes
• additional genetic material resides in plasmids and can replicate independently
• episomes are large circular DNA that can integrate into the bacterial chromosome for replication or stay separate
• bacteria do not have meiosis, therefore no chiasmata or homologous pairs

Question 15

Gene transfer in bacteria

Answer 15

unidirectional - from donor cell to recipient
- never an exchange

Question 16

how can gene mutations be observed in bacteria

Answer 16

• colony colour and morphology
• nutritional mutants (cannot metabolize certain sugars)
• prototrophs (can make AAs needed) and auxotrophs (can’t make AAs needed)
• antibiotic resistance

Question 17

how can you isolate a bacterial strain that cannot synthesize leucine

Answer 17

• plate bacteria on a medium containing leucine, both leu+ and leu- grow
• replica plate the colonies by pressing a velvet surface to the plate, cells adhere to velvet
• Press onto new petri plates,
• leu- are recovered from colony

Question 18

what does a missing colony state

Answer 18

a colony that grows only on the supplemented medium has a mutation in a gene that encodes the synthesis of an essential nutrient

Question 19

how do bacteria exchange genetic material

Answer 19

through parasexual processes
- conjugation
- transformation
- transduction

Question 20

transformation

Answer 20

transfer of a free (out of the cell) piece of DNA from one bacterium into another
- sensitive to DNase
- does not require cell contact

Question 21

conjugation

Answer 21

direct transfer of DNA from one cell to another via the establishment of a cytoplasmic bridge
- not sensitive to DNase (since DNA never touches outside environment)
- requires cell contact

Question 22

transduction

Answer 22

transfer of genes from one cell to another via bacteriophage
- not sensitive to DNase (since virus head is protecting DNA)
- does not require cell contact

Question 23

U-tube experiment

Answer 23

• asks how did the genetic exchange of leucine take place
• 2 different strains of bacteria separated by a barrier that allowed mixing of medium but not bacteria
• since no prototrophic bacteria were produced we conclude genetic exchange requires direct contact between bacteria cells

Question 24

plasmid

Answer 24

an extra-chromosomal circular piece of DNA that can replicate independently of the chromosome
- not required for the survival of host cell and serve as auxiliary genetic elements

Question 25

R plsdmid

Answer 25

resistant plasmids

Question 26

F factor

Answer 26

fertility factor - an episome

Question 27

epsiome

Answer 27

a genetic element that is not essential to the most and that can either replicate autonomously or be integrated into the bacterial chromosome