The Two Meanings of a Biological Vector
In biology, the term 'vector' has two distinct and important meanings. In epidemiology and disease studies, a vector is an organism that transmits an infectious pathogen from one host to another. In molecular biology and genetics, a vector is a DNA molecule used as a vehicle to artificially carry foreign genetic material into another cell, where it can be replicated and/or expressed.
Section 2: The Disease Vector
A disease vector, or epidemiological vector, is any living agent that carries and transmits a pathogen. These vectors do not typically cause the disease themselves but spread it by moving the pathogen between hosts. The most common vectors are arthropods, such as mosquitoes, ticks, fleas, and lice. They acquire the pathogen by feeding on an infected host and then transmit it to a new host during a subsequent feeding.
Section 3: The Cloning or Gene Vector
A cloning vector is a tool used in genetic engineering. It is a small piece of DNA, most commonly a plasmid (a circular DNA molecule from a bacterium) or a modified virus, that is used to carry a specific gene into a host cell. Once inside the host cell, the vector's machinery allows the foreign gene to be copied (cloned) or for its protein product to be made (expressed).
Section 4: Practical Examples of Vectors
A clear example of a disease vector is the Anopheles mosquito, which transmits the Plasmodium parasite that causes malaria in humans. A classic example of a cloning vector is the pBR322 plasmid, which has been widely used in laboratories to introduce genes, such as the gene for human insulin, into E. coli bacteria for mass production.