The Structure and Function of DNA

The instructions that direct the cells to create and use the various materials are contained in the DNA that makes up your chromosomes. That's why DNA is often called the "blueprint of life." Scientists estimate that if the DNA of one cell were stretched out, it would be more than 2 meters long.

In a DNA molecule, the DNA loks much like a long ladder that has been twisted. This arrangement is called a double helix. The sides of the DNA ladder are made up of alternating molecules of sugar and phosphate. Connecting the two sides of the ladder are "rungs" of pairs of special molecules called nucleotide bases.

Only four nucleotide bases make up the rungs of the DNA molecule: adenine, cytosine, guanine, and thymine. They are often denoted by the letters A, C, G, and T.

The sequence of the nucleotides along the DNA molecule determines the type of amino acids that will combine to produce a particular protein. The more DNA in a cell, the more kinds of proteins can be produced.

Humans have 46 chromosomes. The DNA in these chromosomes contains codes for producing thousands of different proteins. Because the DNA is inside the nucleus while the ribosomes that manufacture the proteins are in the cytoplasm, the directions from the DNA must be taken out to the ribosomes. This task is performed by RNA. Each RNA molecule is a copy of a DNA code. When a segment of RNA reaches a ribosome, it is translated. The resulting translation is a protein.