Nucleotide Warm-Up

The structure of DNA:

DNA is made of small molecules, called nucleotides, bound together into a large molecule.  

Here is the basic structure of a nucleotide molecule.  The part highlighted in green is the nitrogen base.  The example here is a two ring structure.  It can also be a one ring structure.  The part of the nucleotide that is highlighted pink is a sugar called deoxyribose.  The part of the nucleotide that is highlighted in blue is a phosphate.  

Below is a picture of how the nucleotides are put together into a DNA molecule.

The base Adenine always bonds with Thymine, and the base Guanine always bonds with Cytosine.  Adenine makes two hydrogen bonds with Thymine and Guanine makes three hydrogen bonds with Cytosine.   A hydrogen bond is a weak electrostatic attraction between charged molecules.  There bonds can be zipped and unzipped, so that the DNA can be copied. 

The backbones of DNA are made by the phosphates bonding to the sugar of the next nucleotide.  Its called a "phosphodiester" bond.  There is lots of water in a cell and inside a cells nucleus. The backbones are hydrophilic, meaning they like water, so they are on the outside of the molecule, facing the water.  The bases are hydrophobic, meaning water fearing,  so they are on the inside of the molecule.