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DNA Structure Cheat Sheet (DRAFT) by

DNA structure ssdasdasdas

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Overview

DNA is composed of four deoxyr­ibo­nuc­leo­tides which are combined through 3′ to 5′ phosph­odi­ester bonds to polymerize into a long chain.
Deoxyr­ibo­nuc­leotide is formed by a combin­ation of base + deoxyr­ibose + phosphate.
Deoxyr­ibose and phosph­odi­ester bonds are the same in all repeating nucleo­tides.
Base sequence is important. The genetic inform­ation is coded in a specific sequence i.e. if the bases are altered then so is the genetic inform­ation being expressed.
Base sequence is written from the 5′ end to the 3′ end.

Four deoxyr­ibo­nuc­leo­tides

DNT
Symbol
Nucleoside
Deoxya­den­ylate (deoxy­ade­nosine 5′-mon­oph­osp­hate)
A, dA, dAMP
Deoxya­den­osine
Deoxyg­uan­ylate (deoxy­gua­nosine 5′-mon­oph­osp­hate)
G, dG, dGMP
Deoxyg­uan­osine
Deoxyt­hym­idylate (deoxy­thy­midine 5′-mon­oph­osp­hate)
T, dT, dTMP
Deoxyt­hym­idine
Deoxyc­yti­dylate (deoxy­cyt­idine 5′-mon­oph­osp­hate)
C, dC, dCMP
Deoxyc­ytidine
 

Salient features of the Watson­-Crick Model

1. Right-­handed double helix: consists of two polyde­oxy­rib­onu­cle­otide chain twisted around one corner in a right handed double helix.
2. Two strands are always comple­mentary to each other.
3. DNA strands are held together mainly by hydrogen bonds between the purines and the pyrimi­dines.
4. Antipa­rallel: one stand runs 5′ to 3′ while the other runs 3′ to 5′.
5. Each strand of DNA has a hydrop­hilic deoxyr­ibose phosphate backbone (3′ to 5′ phosph­odi­ester bond) on the periphery while the hydrop­hobic bases are stacked inside.
6. Diameter of double helix: 2 nm length
7. Each turn/pitch of the helix is 3.4 nm with 10 pairs of nucleo­tides, each pair placed at a distance ~0.34 nm.
8. Genetic inform­ation resides on one of the strands (which is the template stand). The opposite of which is the antisense strand.
9. Double helix has major grooves (1.2 nm) and minor grooves (0.6 nm) along the backbone.

Denatu­ration of DNA strands

Melting Temper­ature (Tm): temper­ature when half of the helical structure is denatured.
Annealing: reasso­ciation of melted strands at lower temper­ature.