DNA is the "Transforming Factor"

The "Transforming Factor"

Frederick Griffith (1908)

Frederick Griffith was working with streptococcus pneumonia bacteria. He was trying to find a cure for pneumonia.

The Experiment

He injected heat-killed bacteria into the mice and nothing happened.
He injected the live bacteria into the mice and nothing happened, but when he mixed the heat-killed bacteria with the live bacteria, together the two were able to kill the mice, or infect it with disease. *substance passed from dead bacteria to live bacteria= the "transforming factor".

DNA is the "Transforming Factor"

Avery, McCarty, & Macleod (1944)

They purified both DNA and proteins from streptococcus pneumonia bacteria.
Question: Which will transform non-pathogenic bacteria?

injected protein into bacteria= no effect.
injected DNA into bacteria= transformed harmless bacteria into virulent bacteria.

Confirmation of DNA

Hershey & Chase (1952)

Classic blender experiment

 

Worked with bacteriophages. *viruses that infect bacteria.

They grew phage viruses in 2 media, and radioactively labeled them with either (35) sulfur, heavy sulfur, in their proteins, and (32) phosphorous, heavy phosphorous, in their DNA.

This experiment confirmed DNA is the "transforming factor".



 

CHI-SQUARED

 

The purpose of a Chi-squared test is to accept or reject a null hypothesis.

The Chi-squared equals the sum of the observed minus the expected; squared and then divided by the expected.

The Null Hypothesis- There is no significant difference between the observed and the expected frequencies.

We take the possibilities minus one to find the degrees of freedom.

Critical Values- the number that determines if we accept or reject the null hypothesis. If the number is > than the critical value; reject.

If the number is < or = to the critical value; accept.

*Critical values don't have to be a whole number.