Concept 22 DNA words are three letters long.

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Marshall Nirenberg, Har Gobind Khorana, and Robert Holley shared the 1968 Nobel Prize for Physiology and Medicine. Nirenberg and Khorana cracked the genetic code. Holley sequenced and deduced the structure of the first tRNA molecule.

Marshall Nirenberg was born in New York City. When he was 12, he and his family moved to Orlando, Florida. His early interest in bird-watching led him to the science of biology. Nirenberg was able to explore the diverse ecology of Florida's wetlands. He also benefited from the instruction provided by professionals - museum curators, biochemists - who were at nearby World War II training camps.

In 1948, Nirenberg graduated from the University of Florida with a Bachelor of Science degree. He stayed at the University of Florida to complete a Master's degree in Zoology on the ecology and taxonomy of caddis flies.

Nirenberg then went to the University of Michigan and in 1957 finished his Ph.D. He had become more interested in the question of life itself and wanted to know the essence. His Ph.D. work on sugar transport in tumor cells reflected his interest in the chemistry of life.

After his Ph.D., Nirenberg went to the National Institutes of Health (NIH) for a 2-year postdoctoral fellowship at the American Cancer Society. In 1960, he accepted the position of research biochemist in the Section of Metabolic Enzymes at the NIH. Nirenberg had already begun working on the problem of how to decipher the RNA code.

In 1961, Nirenberg and J. H. Matthaei published their landmark paper in Proceedings of the National Academy of Science. They showed that a synthetic messenger RNA made of only uracils can direct protein synthesis. The polyU mRNA resulted in a poly-phenylalanine protein ? they had the first piece of the genetic code.

In subsequent years, Nirenberg and his group deciphered the entire genetic code by matching amino acids to synthetic triplet nucleotides. They found that there is redundancy in that some amino acids are encoded by more than one codon and some codons are "punctuation marks" in the mRNA message. Nirenberg and his group also showed that with few exceptions, the genetic code was universal to all life on earth. Nirenberg shared the 1968 Nobel Prize in Physiology or Medicine with Har Gobind Khorana and Robert Holley. Khorana also worked on cracking the genetic code; Holley was the first to sequence a tRNA and determine its structure.

Nirenberg's later research focused on the development of the nervous system of Drosophila melanogaster. He ran a lab in the National Heart, Lung, and Blood Institute of the NIH. He was always passionate about research, the joy of discovery and the wonder of nature's plan.