DNA is Double-Stranded

DNA is a double stranded molecule. Two strands of DNA pair up to form a ladder-like structure that twists on itself. This double spiral of DNA strands is known as a double helix.

The double helix was first discovered in 1956 by two scientists named James Watson and Francis Crick. Here's how the double helix is formed:

1. Two strands of DNA line up next to each other.
   
   
2. The sugar-phosphate portions of the two nucleotide chains form the sides of the ladder.
   
   
3. The bases bond to one another and form the rungs of the ladder.
   
   
4. The ladder twists into a spiral to form the double helix.

Above is a drawing of the DNA "ladder" before it twists into the double helix.