What is a germ?
The term 'germ' actually refers to any microorganism, especially those microorganisms that cause disease. Included in this category are certain viruses, bacteria, and fungi. What is the difference between these three types of microbes? Which ones cause which diseases, and should they be treated differently? Because viruses, bacteria, and fungi cause many well-known diseases, it is common to confuse them, but they are as different as a mouse and an elephant. A look at the size, structure, reproduction, hosts, and diseases caused by each will shed some light on the important differences between these germs.
What is a virus?
Viruses are very tiny, simple organisms. In fact, they are so tiny that they can only be seen with a special, very powerful microscope called an "electron microscope," and they are so simple that they are technically not even considered "alive." There are six characteristics of all living things:
- Adaptation to the environment
- Cellular makeup
- Metabolic processes that obtain and use energy
- Movement response to the environment
- Growth and development
- Reproduction
A virus is not able to metabolize, grow, or reproduce on its own, but must take over a host cell that provides these functions without the aid of a host cell, and is therefore not considered "living." The structure of a virus is extremely simple and is not sufficient for the independent life of the microbe.
Structure: Each virus is made up of two elementary components. The first is a strand of genetic material, either deoxyribonucleic acid (DNA) or ribonucleic acid (RNA). Unlike living cells, viruses will have either DNA or RNA, but not both. The genetic material is a blueprint for determining the structure and behavior of a cell. In a virus, a protein coat called a "capsid" surrounds the nucleic acid. This coat serves to protect the nucleic acid and aid in its transmission between host cells. The capsid is made of many small protein particles called "capsomeres," and can be formed in three general shapes — helical, icosahedral (a 20-sided figure with equilateral triangles on each side), and complex. Some of the more advanced viruses have a third structure that surrounds the capsid. This is called the "envelope" and is composed of a bilipid layer, like the membrane on a cell, and glycoproteins, which are protein and carbohydrate compounds. The envelope serves to disguise the virus to look like a 'real' cell, protecting it from appearing as a foreign substance to the immune system of the host. The structure of a virus is closely related to its mode of reproduction.
Reproduction: A virus's sole purpose is to reproduce, but it needs a host cell to do so. Once a suitable host cell has been located, the virus attaches to the surface of the cell or is ingested into the cell by a process called "phagocytosis." It then releases its genetic material into the cell, and essentially shuts down normal cell processes. The cell stops producing the proteins that it usually makes and uses the new blueprint provided by the virus to begin making viral proteins. The virus uses the cell's energy and materials to produce the nucleic acid and capsomeres to make numerous copies of the original virus. Once these 'clones' are assembled, the virus causes the host cell to rupture, releasing the viruses to infect neighboring cells.