Discovering the rules of complementary base pairing, Erwin Chargaff
Interviewee: Erwin Chargaff. Erwin Chargaff talks about his discovery - a major step for building the DNA model. (DNAi Location: Code > Finding the structure > Players > Erwin Chargaff > Chargaff's ratio)
We found, as I say, that there were constant quantities of each of the nucleotides in a given DNA, that is if we isolated from three different sperm preparations, human DNA, hydrolyzed these separately and determined quantitatively the content in the various nucleotides or, or bases, they would be constant for the species but different for different species. So that for instance we could find the 27 percent adenine, that means also 27 percent thymine, and in the other one we could find 52 percent adenine and 52 percent thymine. So that a compound, these quantitative results were constant for the species but different from each other. So this was something which was completely unusual, unknown in biology, I would say, that these thousands of protein analyses and I don't think one can find a single one in which certain amino acids and identical characteristic amounts that this is repeatable amounts so that this was definitely unique for me at least.
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Erwin Chargaff found that in DNA, the ratios of adenine (A) to thymine (T) and guanine (G) to cytosine (C) are equal. This parity is obvious in the final DNA structure.
Erwin Chargaff talks about his name for Chargaff's ratios.
Because it contains the directions for assembling the components of the cell, DNA is often thought of as the "instruction book" for assembling life.
What happens in protein synthesis?
Fred Sanger outlines DNA sequencing.
James Watson and Francis Crick explain how they solved the structure of DNA. Erwin Chargaff explain how he measured the levels of each of the four nitrogenous bases.
James Watson talks about how he worked out the base pairing of DNA.
George Gamow was a physicist who became interested in biology after reading Watson and Crick's 1953 paper on DNA structure. Marshall Nirenberg talks about Gamow's theories on the code.
DNA has four "letters" that must specify the 20 different amino acids that make up proteins. Combinatorially, using three DNA letters for one amino acid makes the most sense.
Synthesizing human insulin using recombinant DNA, 3D animation with no audio