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2.2 The DNA discovery. Griffith's experiment

0:00     Have you ever wondered what determines

0:01     your height hair and skin colour and even

0:04     the size of your nose? Its DNA, the

0:08     genetic material of cells. But do you know

0:10     how it has been proved? Here is the

0:13     experiment that proved it: Griffith’s

0:15     experiment. Griffith took two strains of

0:18     Pneumococcus bacteria SIII, which have

0:21     smooth polysaccharide capsule, giving

0:24     smooth colonies (S), and its virulent

0:26     causing pneumonia; and RII, which have no

0:30     capsule, giving rough colonies (R) and is

0:33     avirulent, unable to cause pneumonia.

0:35     When the virulent SIII bacteria injected

0:38     in mice, it killed them, causing pneumonia.

0:41     But when the avirulent RII injected in

0:44     mice, the mice lives. if you injected the

0:47     heat killed virulent SIII bacteria, the

0:50     mice still live implying that live SIII

0:53     bacteria are needed for causing

0:55     pneumonia. But interestingly when mice

0:57     were injected with the mixture of heat

0:59     killed virulent SIII bacteria and

1:01     avirulent RII bacteria, mice died.

1:04     Analysis of dead mice reveals live SIII

1:07     virulent bacteria suggesting something

1:10     from the heat killed SIII had transformed

1:12     the live avirulent RII bacteria

1:15     responsible for the transformation of

1:17     the live avirulent bacteria to virulent

1:20     SIII bacteria, causing death of mice. This

1:23     is called as bacterial transformation. To

1:26     prove DNA is genetic material team of

1:29     Avery et al and Hershey and Chase

1:31     performed other experiments.

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