Bacterial and viral genetics

Question 1

Bacteria and viruses

Answer 1

Small genomes compared to animals & plants, high replication rates, demonstrate basic principles of inheritance making bacteria and viruses excellent research tools ( selective media and genetic variability)

Question 2

Bacteriophages

Answer 2

reproduce by infecting bacterial cells, produce plaques (clearances) on plates with dense bacterial cultures within hours of infection

Question 3

Bacteriophage T4

Answer 3

DNA genome, 150 characterized genes and 168 800 bp , genome size is small compared to other organisms but large compared to other viruses

Question 4

Do bacteriophage T4 go thorugh a lytic cycle?

Answer 4

YES

Question 5

Bacteriophage λ

Answer 5

Can be lytic or lysogenic

Question 6

Retrovirus

Answer 6

RNA genome transcribed to DNA, transcribed to DNA by RNA transcriptase, RNA degrades, a complementary DNA strand synthesized and inserted into host genome; Host transcribes viral genes and machinery is synthesized in cytoplasm

Question 7

Bacterial genomes are…

Answer 7

circular molecules of several million bp, called bacterial chromosomes.
Additional genetic material resides in plasmids (small circular DNA loops) that can replicate independently of the bacterial chromosome

Question 8

Episomes

Answer 8

are large circular DNA that can integrate into the bacterial chromosome for replication or can remain separate

Question 9

Gene transfer in bacteria is ….

Answer 9

unidirectional - only donor to recipient

Question 10

Phenotypes in bacteria allow….

Answer 10

gene mutation to be readily observed (no recessive genes) via colony colour and morphology, nutritional mutants

Question 11

Prototroph

Answer 11

synthesizes all nutrients needed

Question 12

Autotroph

Answer 12

Cannot synthesize certain AAs

Question 13

Conjugation

Answer 13

direct transfer of DNA from one cell to another via cytoplasmic bridge.

“Sexual” reproduction mediated by fertility/F factor (an episome), allows building of conjugation channel (cytoplasmic bridge) and other proteins necessary to transfer DNA
Builds pilus (pl. pili) which are flagella that anchor the recipient cell
An F-factor can exist as extrachromosomal DNA (F+ cell) or insert itself into bacterial chromosome (Hfr cell - high frequency recombination)
Homologous regions on F factor allow it to cross over into chromosome
F+ is a precursor to Hfr and cannot create resistance on its own
Conjugation channels are very fragile, any disturbance could break them
Only donor cells have genes that code for building of a conjugation channel (F factor)

Question 14

Transformation

Answer 14

competent bacterial cells take up free DNA from the environment.

Transferred DNA incorporated into recipient bacterial chromosome (stably inherited)
Competence means that bacteria is capable of taking up free DNA from surroundings
Only about 0.2-0.5% of entire bacterial chromosome undergoes transformation (and only occurs with homologous sections of free DNA)
Must be DNA of same species in order to take it up
Transformation is measured as change in phenotype that occurs with a certain frequency (gene linkage can be observed in transforming DNA)

Question 15

Transduction

Answer 15

transfer of DNA from one cell to another via bacteriophage (vector)

As new DNA is being synthesized and taken into capsid, sometimes bacterial DNA is mistakenly incorporated and carried with phage to next infection
Accidental creation of recombinant chromosome when majority is bacterial DNA

Question 16

U-tube experiement

Answer 16

2 strains of auxotrophic bacteria on either side of the tube with a barrier in the middle to eliminate conjugation and a lot of DNase to eliminate transformation.
Bacterial viruses added to tube which allows transduction, they could infect bacteria on one side of the barrier and carry it to the other side, along with that bacterial DNA

Question 17

Which recombination process is cell contact required in?

Answer 17

Conjugation

Question 18

Which recombination process is sensitive to Dnase

Answer 18

Transformation