heat-killed s strain bacteria+r strain when injected into mice, killed it. but how did it happen as s strain was already killed n r strain isn't enough to kill a mice??????
@Jankita:- Your friends are correct. The "transforming principle" given by Griffith revealed that the S strain bacteria had been killed. But the DNA had survived the heating process and was taken up by the R strain bacteria.
@ Prashant and Mercy:- Good job guys. Keep posting!
according to S.F. grifith tranformation took place in RTYPE bacteria when some substance from STYPE entered in the R TYPE. later this was porved by O.T AVERY, Mc CARTYand Mc loed.
they centrifuged STYPEBacteria and obtained carbohydrates, proteins and dna
they took 4 test tubes
TESTTUBE1 : they took RTYPEbacteria and added CARBOHYDRATES to it. ---- no transformation took place.
TESTTUBE2 : they took R TYPE bacteria and added proteins ---- no tranformation took place.
TESTTUBE3 : they took RTYPE bacteria and added DNAof STYPE bacteria to it ---- tranformation took place.
TESTTUBE4:- they took RTYPE and added DNA + DNA LIGASE to it--- no transformation took place.
DNA LIGASEbreaks dna into small fragments.SOthis proved that dna is responsible for transformation FROMRTYPETOSTYPE even when STYPEwas HEATKILLED.
hope it helped.
R strain cannot kill a mice because it is not the infectious kind of mice, but S strain is. When we heat-kill the S-strain ones, the genetic material (DNA) does not get destroyed. But in contact with R-strain bacteria,the genetic content is taken up by the R-strain bacteria, thus making it infectious, resulting in the death of the mice by the infection.
R-strain streptococcus pneumonia doesnot have the potential to kill a mice whereas a S- strain bacteria has the potential to do so. When the S-strain is heat killed the DNA is not destryed but the bacteria losses its ability to kill the mice but when S-strain is injected into a mice with R-strain the S-strain transfers its genetic material into the R-strain transforming it into S-strain and thus killing the mice.