Question

write the DNA double helix ​

Answer 1

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James Watson and Francis Crick put forth in 1953 a double helix model for DNA structure, which was later verified by electron microscopy. Salient features of the Watson and Crick model of DNA are :

• DNA consists of two polynucleotide strands that wind into a right-handed double helix.

• The two strands run in opposite directions; one from the 5' end to the 3' end, while the other from the 3' end to the 5' end.

• The sugar- phosphate backbone lies on the outside of the helix and the bases lieon the inside, perpendicular to the axis of the helix.

• The double helix is stabilized by hydrogen bonding between the bases of the two DNA strands. This gives rise to a ladder-like structure of DNA double helix.

• Adenine always forms two hydrogen bonds with thymine, and guanine forms three hydrogen bonds with cytosine. Thus A - T and C - G are complementary

base pairs and the two strands of the double helix are complementary to each other.