What is the DNA double helix?
Scientist use the term “double helix” to describe DNA’s winding, two-stranded chemical structure. This shape – which looks much like a twisted ladder – gives DNA the power to pass along biological instructions with great precision. To understand DNA’s double helix from a chemical standpoint, picture the sides of the ladder as strands of alternating sugar and phosphate groups – strands that run in opposite directions. Each “rung” of the ladder is made up of two nitrogen bases, paired together by hydrogen bonds. Because of the highly specific nature of this type of chemical pairing, base A always pairs with base T, and likewise C with G. So, if you know the sequence of the bases on one strand of a DNA double helix, it is a simple matter to figure out the sequence of bases on the other strand. DNA’s unique structure enables the molecule to copy itself during cell division. When a cell prepares to divide, the DNA helix splits down the middle and becomes two single strands. These single str
