Question

Watson and Crick determined that the two strands of the phosphate-pentose backbone of DNA forms what structure? How do these two strands run? How do purines and pyrimidines pair? What part of DNA is hyrophilic/hydrophobic and exterior/interior?

Answer 1

Watson and Crick proposed that DNA is made up of two strands that are twisted around each other to form a right-handed helix. Base pairing takes place between a purine and pyrimidine, such as A-T and G-C. The sugar and phosphate groups form the backbone of the structure, while the nitrogenous bases are stacked inside.

Step-by-step explanation:

Watson and Crick proposed that DNA is made up of two strands that are twisted around each other to form a right-handed helix. Base pairing takes place between a purine and pyrimidine on opposite strands so that A pairs with T, and G pairs with C (suggested by Chargaff's Rules). Thus, adenine and thymine are complementary base pairs, and cytosine and guanine are also complementary base pairs.

The two strands are anti-parallel; that is, the 3' end of one strand faces the 5' end of the other strand. The sugar and phosphate of the nucleotides form the backbone of the structure, whereas the nitrogenous bases are stacked inside, like the rungs of a ladder.

Each base pair is separated from the next base pair by a distance of 0.34 nm, and each turn of the helix measures 3.4 nm. Therefore, 10 base pairs are present per turn of the helix. The diameter of the DNA double-helix is 2 nm, and it is uniform throughout.