Although chromosomes were known to contain genes, chromosomes were composed of both protein and DNA — it was unknown which was critical for heredity or how the process occurred. In 1928, Frederick Griffith published his discovery of the phenomenon of transformation (see Griffith's experiment); sixteen years later, in 1944, Oswald Theodore Avery, Colin McLeod and Maclyn McCarty used this phenomenon to isolate and identify the molecule responsible for transformation as DNA.The Hershey-Chase experiment in 1952 identified DNA (rather than protein) as the genetic material of viruses, further evidence that DNA was the molecule responsible for inheritance.
James D. Watson and Francis Crick resolved the structure of DNA in 1953, using the X-ray crystallography work of Rosalind Franklin that indicated the molecule had a helical structure. Their double-helix model paired a sequence of nucleotides with a "complement" on the other strand. This structure not only provided a physical explanation for information contained within the order of the nucleotides, but also a physical mechanism for duplication through separation of strands and the reconstruction of a partner strand based on the nucleotide pairings. Although the structure explained the process of inheritance, it was still unknown how DNA influenced the behavior of cells. In the following years many scientists sought to understand how DNA controls the process of protein production within ribosomes, eventually discovering the transcription of DNA into messenger RNA and uncovering the genetic code which links the nucleotide sequence of messenger RNA to the amino acid sequence of protein.
With this molecular understanding of DNA, an explosion of research based on this understanding of the molecular nature of DNA became possible. The development of chain-termination DNA sequencing in 1977 enabled the determination of nucleotide sequences on DNA, and the PCR method developed by Kary Banks Mullis in 1983 allowed the isolation and amplification of arbitrary segments of DNA. These and other techniques, through the pooled efforts of the Human Genome Project and parallel private effort by Celera Genomics, culminated in the sequencing of the human genome in 2001.
James D. Watson and Francis Crick resolved the structure of DNA in 1953, using the X-ray crystallography work of Rosalind Franklin that indicated the molecule had a helical structure. Their double-helix model paired a sequence of nucleotides with a "complement" on the other strand. This structure not only provided a physical explanation for information contained within the order of the nucleotides, but also a physical mechanism for duplication through separation of strands and the reconstruction of a partner strand based on the nucleotide pairings. Although the structure explained the process of inheritance, it was still unknown how DNA influenced the behavior of cells. In the following years many scientists sought to understand how DNA controls the process of protein production within ribosomes, eventually discovering the transcription of DNA into messenger RNA and uncovering the genetic code which links the nucleotide sequence of messenger RNA to the amino acid sequence of protein.
With this molecular understanding of DNA, an explosion of research based on this understanding of the molecular nature of DNA became possible. The development of chain-termination DNA sequencing in 1977 enabled the determination of nucleotide sequences on DNA, and the PCR method developed by Kary Banks Mullis in 1983 allowed the isolation and amplification of arbitrary segments of DNA. These and other techniques, through the pooled efforts of the Human Genome Project and parallel private effort by Celera Genomics, culminated in the sequencing of the human genome in 2001.
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