Binding Characteristics of DNA, Antigens, and Antibodies
Biotechnology relies heavily on the use of biological mechanisms that already exist in nature. A good example is the use and manipulation of complementary molecules. Two important complementary relationships to understand in biotechnology are between antigens and antibodies, as well as between different DNA strands and other nucleic acids.
Antigens are any foreign material that invade our bodies and cause the release of antibodies by the immune system. Antibodies are specifically designed proteins that stick to the foreign material that come into the body so that other "killer" cells can recognize them and destroy them. The immune system makes antibodies to fit specific antigens. For example, an antibody made against a cold virus will not be effective against the chicken pox virus.
Related antigens and antibodies are therefore "attracted" to each other. This bonding characteristic of antigens and antibodies is used in developing many new biotechnology drugs and diagnostics, and is an important part of many other applications.
Protein Power!
Proteins are essential chemical compounds that are made of amino acids. Many important working molecules in the human body are proteins. Antibodies are proteins and every enzyme is a protein. The difference between the proteins (whether enzyme, antibody, or hormone) is in the arrangement of the amino acids.
Protein is not all about meat and eggs. Meat, eggs, beans, and nuts contain a lot of protein compounds. When these foods are eaten, protein from them is broken down into amino acids and some of these amino acids are used to build new proteins in the body.
DNA is made of smaller parts, called nucleotides, that are strung together into a strand. A fully functioning DNA molecule has two of these strands that are attached to each other at each nucleotide. There are four different types of nucleotides: adenine, guanine, cytosine, and thymine, commonly known as A, G, C, and T. These nucleotides can only bond from one strand to the other in one way: A always bonds with T, and C always bonds with G. They are referred to as "complementary."
A double-stranded DNA molecule is called a double helix.
When the two strands are separated, the result is two single-stranded DNAs. These two single-stranded DNAs "recognize" their complementary partner and attempt to bond. A DNA molecule within a cell separates when the cell needs to retrieve the information contained within it to carry out a certain activity. For example, before cell division can happen, the DNA in the cell has to be doubled so that each resulting cell has the same genetic information. In this instance, the DNA splits into two single-stranded DNAs and a complementary version of each strand is copied. This results in two double helix DNA molecules.
There are other nucleic acids that work with DNA that are complementary to DNA. One of these nucleic acids is RNA, which is used extensively in protein production. One type of RNA is called messenger RNA or mRNA for short.
mRNAs are used in the expression of a gene. Expressed genes are those that have been "turned into" proteins, which are the functional products of genes. A gene may code for something to happen, but in order for that something to happen, a protein must be produced to do the work.
Protein production can be broken down into two steps: transcription and translation. mRNAs are used in transcription.
Transcription
Once the cell is ready to make a certain protein, a segment of the double-stranded DNA responsible for that protein code unravels so that it temporarily becomes two single strands. The mRNA then makes a complementary copy of one single strand of DNA, nucleotide by nucleotide. The mRNA, which is then an exact complementary version of the DNA strand, travels out of the nucleus into the body of the cell.
Translation
Once in the body of the cell, the mRNA goes through a molecule called the ribosome. The ribosome can "read" the information contained in the mRNA. Then, with the help of an enzyme called RNA polymerase, the ribosome builds the protein structure, amino acid by amino acid.
Griffiths, Anthony J. F. et al. An Introduction to Genetic Analysis, 6th edition. W.H. Freeman and Company: New York, 1996.
Basic Genetics. gslc.genetics.utah.edu/basic/index.html