Q.Describe in detail the structure of a nucleotide and explain the Watson-Crick double-helix model of DNA structure, including complementary base pairing, and briefly describe the structure and roles of the three principal types of RNA.
You're viewing a preview — the full solution, concept, methods & PYQ mapping are locked.
Start your 14-day free trial to unlock the full solution →A nucleotide, the monomer of a nucleic acid, is composed of three parts: a nitrogenous base (a purine -- adenine or guanine -- or a pyrimidine -- cytosine, thymine or uracil), a five-carbon pentose sugar, and one or more phosphate groups. A base joined only to the sugar (no phosphate) is a nucleoside; adding phosphate group(s) produces a nucleotide, and nucleotides link end to end through phosphodiester bonds to form the sugar-phosphate backbone of a nucleic acid strand.
James Watson and Francis Crick resolved the structure of DNA in 1953, building on Rosalind Franklin's and Maurice Wilkins's X-ray diffraction data, as a double helix: two polynucleotide strands, running in opposite (antiparallel) directions, wound around a common axis in a right-handed coil with about ten base pairs per turn. The sugar-phosphate backbones (built on the sugar deoxyribose) lie on the outside, while the nitrogenous bases project inward and pair according to a strict complementary rule -- adenine with thymine through two hydrogen bonds, and guanine with cytosine through three hydrogen bonds -- so the sequence on one strand exactly dictates the sequence on the other, the structural basis for both storing and faithfully copying genetic information. …
Unlock everything free for 14 days
- Full step-by-step solutions
- Concept-first explanations
- Methods, shortcuts & mistakes
- PYQ mapping + timed mock tests
Full access for 14 days. No credit card required.