By examining the structure of DNA, it is easier and clearer to see what factors are taken into account when genes are passed from parents to offspring. DNA is part of an elite group of compounds called nucleic acids. Nucleic acids are polymers made up of monomers called nucleotides. DNA provides directions for its own replication, directs the synthesis of ribonucleic acid (RNA), and also controls protein synthesis. The entire process is better known as gene expression. On a DNA molecule, each gene directs the synthesis of a special type of RNA called messenger RNA. This mRNA molecule works in conjunction with the cell's protein synthesis machinery to direct the production of a polypeptide chain, which ultimately leads to the formation of a protein. Protein synthesis occurs on ribosomes. However, DNA is found in the nucleus. Nucleic acids include several components. They are macromolecules that exist in the form known as polynucleotides. As mentioned above, monomers of polynucleotides are nucleotides. A nucleotide is made up of three parts: a pentose sugar, a nitrogen-containing base, and a phosphate group. The sugar found in DNA is deoxyribose (lacking an oxygen atom on the second carbon of the ring) and in RNA it is ribose. There are four nitrogenous bases in DNA. Each nitrogenous base has one or two rings that include nitrogen