DNA is short for deoxyribonucleic acid. This chemical is the most important and most complicated chemical in the cell. This chemical holds all of our genes. This combination of genes is needed to perform every task that the cell must do. These genes are unique combinations of chemicals that can be thought of as the recipes for life. The entire DNA molecule, therefore, can be considered the recipe book of the body. Every cell in the body has the same recipe book. That is to say that every cell has an exact copy of the entire DNA molecule; yet every cell is not identical to every other cell.
Figure 1 Representation of the DNA molecule as a Cookbook with all the recipes of life. While each Cookbook within the cell is identical, the difference is that the different cells can only open certain chapters that pertain to their functions.
This DNA recipe book is divided into “chapters” each “chapter” has the recipes for each type of cell of the body. Within each chapter are the individual recipes for that particular cell. Although each cell has a full copy of the DNA – only the “chapter” that relates to that cell can be read by that cell. The rest of the “chapters” are closed. For example, the eye cells cannot read the recipes for the ear cells. This replication of the entire DNA molecule inside every cell is what enables ceratin animals to re-grow whole lost limbs or allows scientists to clone a whole sheep from just one cell. This fact is also taken advantage of by viruses that want to change the function of a cell for their benefit. A virus may infect a cell and change the recipe book by inserting its own version of DNA for instructions on how to make new viruses.
A virus is not considered a living creature because it cannot carry on the biologic functions to allow it to reproduce by itself; it must use the machinery of a cell to accomplish any biologic function. A virus usually contains Deoxyribonucleic Acid (DNA) which is the molecule that takes over the control of a cell’s functions. A virus must also have a method to gain entry into a cell which are usually specific enzymes that attach to a cell and allow entry into the cell without damage.