An analogy is when two things are compared that are alike in some way. Adenine and thymine are complementary base pairs in the deoxyribonucleic acid molecule and they bond together. They are nitrogenous bases. The other two base pairs that are complementary in the DNA genetic code are guanine and cytosine. These bond together in the DNA double helix molecule. Another science analogy is brick:building as cell:organism. This infers the relationship that a building block of a structure is a brick and a cell is a building block of an organism. Enzyme is to substrate, as a lock is to a key is another analogy. They are similar because enzymes bind to specific substrates at their active sites and the shapes are complementary. This is comparable to a specific key fitting into a specific lock. When one observes, one can make an analogy about many concepts in science.