Extracting DNA from Eukaryotic Cells

Background DNA stores and transmits genetic information Where is DNA located? In the nucleus of Eukaryotic cells What cells are we using? Plant cells from strawberries and animal cell from a calf thymus gland

Background Why thymus gland and where is it located? Thymus acts as an endocrine gland as part of your immune system. Responsible for teaching “T” cells to recognize foreign invaders. Thymus cells have very large nuclei and thus are rich in DNA.

1. (I) Breaking Down the Tissue Thymus Strawberries Crushing releases the cells into solution. The tissues lose their shape.

Cell Membrane Structure 2. (II) Breaking Open the Cell Membranes and Nuclei The extraction buffer (soap and salt) causes the forces that hold the cell and nuclear membranes together to break down. This “clouds” the mixture. Cell Membrane Structure

Positive (+) ions from the salt neutralize the negatively (-) charged phosphate group so that DNA is no longer soluble. The DNA can coil upon itself and begin to precipitate (“un-dissolve”). Salt ion (Na +) (-) Nucleotide

3. (III) Collecting the DNA DNA is soluble in water but not ethanol. Addition of ethanol allows DNA to further precipitate out (“un-dissolve”). The ethanol is less dense than water and the DNA is less dense then ethanol, so the “snotty” DNA rises to the surface.

4. DNA is clear when wet (soluable in water), but sticks and coils in the presence of salt and ethanol (insoluable in those). Procedures for plant and animal very similar. Animal cells require sand during crushing b/c tissue is tougher. ALL human cells contain DNA. Extracted DNA can be used for analysis, cloning, and recombination. These applications can cure disease, produce better food crops, and more (though there are ethical issues).

Final Note Every diploid cell in the human body contains about 3 billion base pairs (bp) of DNA in 46 chromosomes. This is known as the “human genome.” At actual stretched-out size, a single human cell's DNA is about 3 meters in length. The total length of DNA present in ALL the cells of one adult human (about 10 trillion cells) is the equivalent to the distance from the earth to the sun and back.