NBME form 3 block 1 question 12...please help!!! - rim0209

[ArchivalUser]

Bacterial strain X is resistant to ampicillin and sensitive to gentamicin,bacterial strain Y is resistant to gentamicin and sensitive to ampicillin .Bacterial strains X and Y are grown in mixed culture medium without antibiotics,then the culture is plated on medium containing both gentamicin and ampicillin.Bacterial colonies grow on the plates. In second experiment DNase is added to mixed culture medium.When this mixed culture medium is plated on medium containing both antibiotics ,no colonies grow.Assuming that bacterial cell is impermeable to DNase, which of the following processed best explains these observation?
a.Conjgation
b.mutation
c.transduction
d.transformation
e.transposition

the key says D can somebody please explain the answer. thanks.

[ArchivalUser]

I assumed it had to do with plasmid carrying the drug resistance, which is then degraded by the DNase leading to loss of resistance

[ArchivalUser]

the answer id D..Transformation....

Answer by yeabiruh.

--Bacterial X =Ampicillin Resisitant and Gentamicin Sensitive
--Bacterial y=Ampicillin Sensitive and Gentamicin Resisitant

--First Experimen =No DNase added and X and Y grow in mixed CULTURE with Amp and Gen
outcome=colnies GROW

--Second Experiment=DNase added and X and Y grow in mixed culture with Amp and Gen
outcome =no colnies GROW

--the difference between the first and second experiment is the ADDITION of DNase

--DNase breaks down naked Chromosomes ..

--In the first experiment there is growth because the bacterias can take naked DNA from the suurounding By TRANSFORMATION =gets the antibiotic resistance

--in the second experiment there is no GROWTH because there is no AVAILABLE DNA to be taken from the environment by TRANSFORMATION due to the action of DNase=NO antibiotic resistance =no growth

hence my answer dddd

[ArchivalUser]

thanks shells makes sense now ...it can't be the plasmid like shell said naked DNA is destroyed by Dnase and the only form of exchange where this happens is transformation.the question also says that the cell is impermeable to DNase so it cant penetrate and destroy the DNA inside the bacterial cell.