![]() ![]() ❖ Chargaff’s parity rule1 : In any given DNA sample from any species, the total percentage content of Adenine is equal to that of Thymine, and the total percentage contents of Guanine and Cytosine are the same. The deductions regarding the base pairing of nucleotides in DNA molecules is as follows. Later, when Watson and Crick established the structure of DNA, the concept of base pairing was more comprehensively understood. The rules for DNA base pairing were laid down based on the experimental findings of Erwin Chargaff. The four bases can be divided into two categories based on their chemical structures. Due to the presence of deoxygenated ribose sugars, the structure, DNA, is called deoxyribonucleic acid. Nucleotides use these phosphate groups to link together via the formation of phosphodiester bonds, and bond to their complementary bases using hydrogen bonds. When they gain one or more phosphate groups, they are then termed as nucleotides. These nitrogenous bases in conjugation with a deoxyribose sugar, are called nucleosides. A nucleobase is an alternative term used for a nitrogenous base. It shows the presence of four unique nucleobases, whose arrangement in random sequences leads to the formation of the genetic code of an organism. ![]() ![]() The structure consists of two DNA strands linked to each other with the help of hydrogen bonds, and arranged in a spiral manner. With the discovery of the chemical structure of DNA, by Watson and Crick in 1953, the double helical structure of DNA and the arrangement of the bases in the said structure was revealed. In 1962, James Watson, Francis Crick, and Maurice Wilkins received the Nobel prize for their discovery of the chemical structure of DNA, and its base pairing pattern. ![]()
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