IV.

Other Contributions to Genetics

Crick received his Ph.D. from Cambridge University in 1953. He then worked briefly with Watson on the structure of viruses. But he eventually returned to the study of DNA and his findings led to rapid advances in genetics. He and his coworkers determined how the order of bases, chemical subunits on the DNA structure, act as a code to determine the sequence of amino acids that make up proteins. With South African-born British geneticist Sydney Brenner, Crick identified that codons, groups of three bases, provide instructions for the creation of all 20 amino acids.

Crick made two sweeping theories that have stood the test of time. In his adaptor hypothesis, he theorized that small molecules of ribonucleic acid (RNA) and enzymes work as intermediaries between DNA and amino acids during protein synthesis. Initially met with skepticism in the science community, the theory was eventually proven correct with the discovery of transfer RNA and adaptor enzymes. Crick also theorized that the flow of genetic information is from DNA to RNA to protein, and that genetic information cannot flow the other way, from protein to RNA to DNA. This theory has been tested repeatedly since Crick discussed it at a meeting of the Society of Experimental Biology in 1957, and it is now called the central dogma, a crucial principle of molecular biology.