THE BLUEPRINT OF LIFE

Problem. What controls heredity ? What makes you grow up to look like you and not someone else? The answer to this question is the key to life.

Background. For centuries men have wondered why men look like men. Some people thought that the blood of a mother and father mixed and the characteristics carried in the blood of the parents were passed on to the children.This theory was proven false in 1902, when Walter Sutton discovered the chromosomes. The chromosomes are tiny threadlike structures in the nucleus of a cell that contain the heredity of the cell.

Each human cell has forty-six chromosomes, which are split into forty-six identical pairs whenever the cells divide. Each of the daughter cells receives one-half of the chromosomes. But scientists did not know why or how the chromosomes split into two identical groups.

Explanation. The key discovery in the study of heredity was made by molecular biologists who discovered the chemical make-up of the chromosomes. They found that the chromosomes are made of a certain nucleic acid, called deoxyribonucleic acid. Biologists usually refer to this by its abbreviation, DNA.

In 1953 Doctors Francis Crick and James Watson perfected a three-dimensional model that explained all the characteristics of DNA. The model showed that the molecule was shaped like a spiral staircase. The sides of the stair treads were made of two chemicals and the "treads" were made of four other chemicals.

 

Many experiments proved that it is the arrangement of these four kinds of "treads" that determines a person’s characteristics.

The cells of the body contain about three feet of DNA, if the molecules are laid end-to-end. There are three or four encyclopedias of information in these DNA molecules. They use another nucleic acid, RNA (ribonucleic acid), to translate this information into the proteins that make up new tissue.

Further research. For an excellent discussion of DNA, read The Cell, one of the books in the Life Science Library.