DNA
A nice picture having some basic information on DNA, click on the picture to get the larger view.
A VERY NICE MOVIE on the coiling of DNA in the human cell... It is just an astonishing art to put 2 meters long DNA (46 single DNA molecules known as chromosomes, each has a length of around 4 to 5 cm) into a single cell having dimensions around 0.005 mm.
The above picture shows a circular DNA (found in bacteria) in different supercoiling states, as the image in the first window corresponds a highly supercoiled state while the last one is a relax DNA.