What is DNA? DNA is a nucleic acid made up of nucleotides joined into long strands or chains by a covalent bonds. Nucleic acids are long molecules found in cell nuclei. They are made up of smaller subunits or parts. These parts consist of three basic parts: a 5-carbon sugar called deoxyribose, a phosphate group, and a nitrogenous base. All the parts are linked together to form long chains.
Nitrogenous bases are bases that have nitrogen in them. DNA has four kinds of nitrogenous bases which include adenine, guanine, cytosine, and thymine. Each of these bases are held together by a hydrogen bond. In order for the bases to be with their partner in order to work called base pairing. Therefore, A (adenine) goes with T (thymine) and C (cytosine) goes with (guanine).
Erwin Chargaff had discovered that the percentages of A and T bases are almost equal in any sample of DNA which also works for G and C. DNA samples from organisms as different as bacteria and humans obeyed this rule, but no one knew why they did.
James Watson and Francis Crick tried to understand the structure of DNA. They tried to build many models of the possible DNA structure out of cardboard and wire. But nothing ever worked. Then, in 1953 Watson saw a copy of Franklin’s X-ray picture and suddenly figured out the missing piece. Later on, he ran to Crick to tell him that they had figured out the structure of DNA which was called the double-helix model. In a double-helix model two strands of DNA run in opposite directions and explains Chargaff’s rule of base pairing and how the two strands of DNA are held together.
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