| MadSci Network: Molecular Biology |
DNA stands for DeoxyriboNucleic Acid, which is a polymer of phosphorylated sugars with a purine or pyrimidine base attached to each sugar. DNA can be a single strand, as in some phages (viruses that attack bacteria), but it is usually double stran ded (in the form of a helix). As it happens, DNA is used by most organisms as the primary genetic material.
Genes are units of genetic information. Each gene encodes a message which, in turn, produces a specific component (usually a protein) of the organism. For example, the genes for skin color produce enzymes that form a compound called melanin which acts as a brown pigment. When the gene is expressed at high levels, there is a lot of melanin produced, making the skin darker; when the gene is expressed at low levels, there is much less melanin produced, making the skin lighter. Since genes are the units of genetic in formation, and DNA is the primary genetic material, then genes are made of DNA.
All of the genes of an organism are referred to collectively as that organism's genome. The genome is physically subdivided into chromosomes, which are the individual pieces of DNA which contain the genome. Most bacteria have a single chro mosome which contains the entire bacterial genome. Humans have 46 chromosomes - 46 separate pieces of DNA - of various sizes each carrying its share of genes along with a lot of filler which codes for nothing. Together, the 46 chromosomes contain the en tire human genome. So genes are made of DNA, like records are made of vinyl, but not all DNA is genes, like the part of the record that has no grooves.