Dna Extraction

Lab Exercise

DNA Extraction

10/30/13

DNA in all organisms is found primarily in chromosomes. Eukaryotic cells, like those found in humans, contain several linear chromosomes. Prokaryotic cells, such as bacteria, contain one large circular chromosome.

DNA is composed of building blocks called nucleotides, each made up of a five-carbon sugar (deoxyribose), a phosphate group, and a nitrogenous base. The four kinds of nucleotides differ only in their nitrogenous bases. It is the nucleotides and their bonding pattern that give DNA its unique characteristics and functions. Structurally, DNA contains two long strands of bonded nucleotides. These strands run in opposite directions. The two long strands are connected by hydrogen bonding between the nitrogen bases of the nucleotides (A-T and C-G). Each bonded pair of nucleotides is called a base pair. An average gene consists of a sequence of approximately 3000 base pairs.

The functional units of DNA, the genes, code for polypeptides which serve countless functions for the cell. Without proteins (for example, enzymes), the chemical reactions that make up a cell’s metabolism could not proceed in a timely manner and the cell would die. Bacterial chromosomes contain approximately 3000 genes. Humans, on the other hand, contain about 20,000-25,000 genes in each of their cells. If all of the DNA in all of the cells of a human were stretched end to end, it would form a ladder 100 billion kilometers (you could climb to the sun and back 300 times).

Today, you will extract DNA from the bacterium Micrococcus luteus. The first step is to lyse (burst) the M. luteus cells to release the DNA into the solution. In order to do this, a detergent used in laundry products called SDS (sodium dodecyl sulfate) is used to degrade lipids in the bacterial cell membrane. When the cell membrane is damaged, the cell lyses, releasing the cytoplasm’s contents into the solution. This causes the solution...