What did earlier work on DNA demonstrate about its composition and base-pairing rules?

What did earlier work on DNA demonstrate about its composition and base-pairing rules?

• A. DNA is composed of nucleotides consisting of deoxyribose sugar, a phosphate group and 1 of 4 nitrogenous bases (A, T, C, G). Phosphate and sugars of adjacent nucleotides link together and ratios of A-T, C-G are constant
• B. DNA is a polymer of amino acids
• C. DNA contains glucose units and lipids
• D. DNA is identical to RNA in sugar type

Answer: (A)

DNA is built from nucleotides that have a deoxyribose sugar, a phosphate group, and one of four nitrogenous bases. These nucleotides link through phosphodiester bonds to form a sugar–phosphate backbone. Early work showed that, within any given organism, the amounts of adenine and thymine are equal and the amounts of cytosine and guanine are equal, even though the total amounts of each base can vary between species. This observation—often summarized as Chargaff’s rules—pointed to a specific pairing between bases: adenine pairs with thymine and cytosine pairs with guanine on the two strands of the double helix. This complementary base pairing is what makes the composition and the base-pairing rules of DNA such and so crucial for accurate replication and heredity.

DNA is built from nucleotides that have a deoxyribose sugar, a phosphate group, and one of four nitrogenous bases. These nucleotides link through phosphodiester bonds to form a sugar–phosphate backbone. Early work showed that, within any given organism, the amounts of adenine and thymine are equal and the amounts of cytosine and guanine are equal, even though the total amounts of each base can vary between species. This observation—often summarized as Chargaff’s rules—pointed to a specific pairing between bases: adenine pairs with thymine and cytosine pairs with guanine on the two strands of the double helix. This complementary base pairing is what makes the composition and the base-pairing rules of DNA such and so crucial for accurate replication and heredity.