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- In 1928, Fred Griffith discovered transfoormation when he showed that harmless bacteria could turn virulent when they were mixed with bacteria that caused disease.
- In 1944, Oswald Avery demonstrated that DDNA responsible for capsule formation on the dead bacteria transformed the genetic code of the live bacteria.
- In 1952, Alfred Hershey and Martha Chase used the bacteriophage T2 and radioactive labels to identify DNA as the genetic material.
- P.A. Levine showed that DNA can be brokenn down into a sugar, a phosphate group, and four nitrogen-containing bases (adenine, guanine, thymine, and cytosine).
- A nucleotide contains one base, a sugar, and a phosphate group.
- In 1949, Erwin Chargaff determined that ffor the DNA in each organism, the amount of adenine always equals the amount of thymine, and the amount of guanine always equals the amount of cytosine. These findings, known as the base-pairing rules, suggested that the precise arrangement of nucleotides within a DNA molecule specifies genes.
- In 1953, James Watson and Francis Crick pproposed a model that illustrated the structure of DNA. This model shows that DNA is a union of two polynucleotide chains forming a double helix.
- In DNA replication, enzymes work to unwinnd and separate the double helix into two strands. Each strand is used as a template to build a complimentary strand. When the complementary strand is complete, it twists with the template strand to form a double helix.
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