All living things are made up of cells. Cells carry out various functions in living organisms and the functions of cells are very specific to each type of cell. A nerve cell has a different function than a bone cell or an eye cell. The two main categories of cells are prokaryotic and eukaryotic cells. Prokaryotic cells are cells that lack a membrane bound nucleus, are small in size and are fairly simple. A common example of a prokaryotic cell is a bacterial cell. Eukaryotic cells are cells that have a membrane bound nucleus, are larger in size and are much more complex containing more organelles than prokaryotic cells. The cells that make up our bodies are eukaryotic cells. Although prokaryotic cells and eukaryotic cells are very different they do share a few similarities. Both contain genetic information (DNA), a cell membrane or cell wall to contain internal structures and ribosomes.