3-D version (requires Chime)

A complete DNA molecule consists of two polymers (DNA chains) twisted into a double helix. The two strands of a DNA molecule are held together by hydrogen bonds between the bases on opposite strands. The strands are only held together by weak H-bonds, but any particular DNA molecule may have millions of these weak bonds, so in conbination, the H-Bonds keep the two strands together.

In the Nucleus of a cell, DNA is packaged into chromosomes. In Humans, our 46 chromosomes carry about 50,000 genes in a row along their length. All the DNA, in the form of chromosomes is found in the nucleus of a cell.To understand why DNA is organized into chromosomes, we must appreciate the fact that the nucleus is only 6 micrometers in diameter (very small). and the total length of DNA in the nucleus is about six feet, that's six feet of DNA in each cell of your body! Thus, in order to pack the DNA into the nucleus, there must be several levels of coiling and winding. Each chromosome contains 1 long molecule of DNA (two strands) plus associated histones (a sort of round protein) which help in the condensation of DNA. The DNA is wound around the Histone proteins like sewing thread is wound around a spool. The DNA/Protein complex is called Chromatin.

Isolation of DNA from Onion leaves- To extract DNA from cells you must break them open and then solubilize the DNA. Solubilization of DNA can be difficult because it is such a large molecule. To facilitate the solubilization, we will use a little detergent. The detergent also removes many of the proteins found associated with DNA. To isolate the DNA from the aqueous /detergent solution we add cold ethanol (EtOH). DNA is not soluble in cold EtOH and will "precipitate".