Griffith's experiment worked with two types of pneumococcal bacteria (a rough type and a smooth type) and identified that a "transforming principle" could transform them from one type to another.
At first, bacteriologists suspected the transforming factor was a protein. The "transforming principle" could be precipitated with alcohol, which showed that it was not a carbohydrate. But Avery and McCarty observed that proteases (enzymes that degrade proteins) did not destroy the transforming principle. Neither did lipases (enzymes that digest lipids). Later they found that the transforming substance was made of nucleic acids but ribonuclease (which digests RNA) did not inactivate the substance. By this method, they were able to obtain small amounts of highly purified transforming principle, which they could then analyze through other tests to determine its identity, which corresponded to DNA.
To protect them from ultraviolet rays from the sun.
Answer:
Through the study of meteorites, their chemical composition of silicates—material made of silicon and oxygen. Others contain metal—nickel and iron. Knowing what the meteorite was composed of lets you know where it came from. Chondrites are composed of hardened lava - this is occurred at the beginning of the solar system (4.5 mya). Carbonaceous chondrites contain carbon and water which formed away from the sun.
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