True about DNA structure: (PGI Nov 2010)
Ans; C (Deoxy..) "In the DNA helix, hydrophilic deoxyribose-phosphate buckboneQ of each chain is on the outside of the molecule, whereas the hydrophobic bases are stacked insideQ"- Lippincott' Biochemistry 4th/397"DNA is covalently linked by 3'-5' phosphodiester bondQ"- Lippincott' Biochemistry 4th/397"There are 3 form of DNA- B, A&Z. B-DNA & A-DNA forms right handed helix whereas Z-DNA forms left handed helix. Chromosomal DNA is thought to be predominantly B-DNA"- Lippincott' Biochemistry 4th/ 397(So consists primarily of right handed helix) "Lippincott' Biochemistry 4th/ 397DNA StructureThe structure of DNA is illustrated by a right bonded double helix, with about 10 nucleotide pairs per helical turn. Each spiral strand, composed of a sugar phosphate backbone and attached bases, is connected to a complementary strand by hydrogen bonding (non- covalent) between paired bases, adenine (A) with thymine (T) and guanine (G) with cytosine (C)QThe structure of DNA of all species comprises two helical chains each coiled round the same axis, and each with a pitch of 34 Angstroms (3.4 nanometres) and a radius of 10 Angstroms (1.0 nanometres).Adenine and thymine are connected by two hydrogen bonds (non-covalent) while guanine and cytosine are connected by three.This structure was first described by James Watson and Francis Crick in 1953QAlthough the 'B-DNA form' is most common under the conditions* found in cells, it is not a well-defined conformation but a family of related DNA conformations that occur at the high hydration levels present in living cells.Compared to B-DNA, the A-DNA form is a wider right- handed spiral, with a shallow, wide minor groove and a narrower, deeper major groove. The A form occurs under non-physiological conditions in partially dehydrated samples of DNA
Purines are adenine and guanine ; pyrimidines are uracil and cyTosine
Watson and Crick discovered structure in 1973
Doxyribose-phosphate backbone with bases stacked inside
Mainly consists of left handed helix
Immunology