Diagram 1 shows examples of base-paring of bases in an unraveled double helix. Note how adenine (A) pairs with thymine (T), and Cystosine (C) pairs with Guanine (G). Diagram 2 shows a model of the shape of the DNA double helix.

Before we get started, we will first discuss several scientific terms and techniques that readers may encounter. Make sure you thoroughly understand all of them before preceding!

DNA, or deoxyribonucleic acid, is the molecule that acts as the universal code of life for all living organisms, and is passed down from generation to generation. DNA is what makes all living organisms unique; it is why a cat becomes a cat, and a dog becomes a dog. DNA influences the development of an organism primarily by encoding for another type of molecule which produces proteins; it is regulated by complex internal and external chemical interactions. When viewed in the cell, it is usually visible only as a dark, highly dense small blob. DNA is made of only 4 different units known as nucleotide bases, which are paired together with hydrogen bonds: adenine, guanine, cytosine, and thymine (see Diagram 1). Each individual DNA molecule consists of two strands which fit together and wind around each other in the shape of a spiral staircase known as a double helix (see Diagram 2). Adenine always pairs with thymine, and cytosine always pairs with guanine.The two strands that make up a DNA molecule are known to be complementary to each other because every base on one strand pairs with another base on the second strand. For example, if a strand consisted of ATGCC, the complementary strand would be:  TACGG. Notice how the bases on the two strands in the picture pair up nicely.

Because DNA is the genetic material of all living things, scientists sequence DNA in hopes of deciphering secrets including but not limited to, the evolutionary relationships between species, cures to genetic disorders, the structure of proteins, genetic defects, and the molecular structure of a gene. (8) For more information on DNA, visit: http://www.genome.gov/25520880

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