DNA : The molecule of Life All living things are made of cells. The adult human body contains approx. 100,000,000,000,000 cells. There are 200 different cell types in humans – some of which are shown above – can you name them? Each cell has a nucleus which contains all the Informa@on in the form of DNA (dioxyribonucleic acid) to make a complete animal (even us). DNA is composed of two long linear strands of fours bases (A,T,G,C) which are link together in a double helix (note each A is paired with a T and each G is paired with a C). Stretches of DNA make up genes (of which there are about 24,000 in humans). Each human cell contains 6,400,000,000 base pairs of DNA that is packaged up into chromosomes. How many base pairs in an adult human being? By using restric@on enzymes (proteins) that cut DNA at very precise places (restric@on sites), researchers can chop, cut and paste DNA at will to create plasmids which can be introduced into bacteria to amplify them. This is the basis of molecular cloning. This allows researchers to study genes that contribute to human disease. Can you name a human gene? What does it do? Today you are going to do some of the key steps in molecular cloning. When circular DNA plasmids are digested with restric@on enzymes the linear fragments can be separated by gel electrophoresis. The gel contains small holes in it that the DNA can move through. The smaller the DNA fragment the further they move in response to a current. How would you work out where the restric@on sites are in the original circular plasmid?