1.2 Structure of DNA - Oronda/Molecular_biology_concepts GitHub Wiki

DNA is a double-stranded helix, with the two strands connected by hydrogen bonds. A bases are always paired with Ts, and Cs are always paired with Gs, which is consistent with and accounts for Chargaff's rule.

Most DNA double helices are right-handed; that is, if you were to hold your right hand out, with your thumb pointed up and your fingers curled around your thumb, your thumb would represent the axis of the helix and your fingers would represent the sugarphosphate backbone. Only one type of DNA, called Z-DNA, is left-handed.

The DNA double helix is anti-parallel, which means that the 5' end of one strand is paired with the 3' end of its complementary strand (and vice versa). Nucleotides are linked to each other by their phosphate groups, which bind the 3' end of one sugar to the 5' end of the next sugar.

Not only are the DNA base pairs connected via hydrogen bonding, but the outer edges of the nitrogen-containing bases are exposed and available for potential hydrogen bonding as well. These hydrogen bonds provide easy access to the DNA for other molecules, including the proteins that play vital roles in the replication and expression of DNA.

DNA consists of two parallel chains twisted to form a double helix. The 2 DNA chains/strands run in opposite direction. The 2 chains are cross-linked at regular intervals corresponding to nucleotides. Each base pair is 3.4A o /0.34 nm from each other along the double helix and is turn 36o from the preceding one. Ten nucleotides for one complete turn of the helix which is 360 degrees and 34 Ao /3.4 nm.

DNA DS molecule is like a twisted ladder with phosphate group as the steps. Links appear as bases sticking inwards towards each other. There is a Special relationship that links A with T, and G with C. T and C are pyrimidine bases with single hexagonal rings. A and G are purines with double hexagonal rings. The Rings in DNA can only be formed by linking a purine and a pyrimidine.