Glossary
Starting with A for "ACE inhibitor" and continuing through to Y for "Yolk Sac Tumour", we give you succinct explanations for scientific and medical terms in clear and simple words.
- VirusesCollective name for the biological structures, which in the known cases mostly cause disease, and which have the following common characteristics: 1. The genetic information is only either DNA or RNA; 2. They do not possess the enzymes which are necessary for growth and reproduction, but require for this purpose host cells which are usually specific and which may be plant cells or certain animal or human cells, in which they often cause disease. Viruses which only attack bacteria are called bacteriophages. The modern classification of viruses is mostly based on their structure and genetic similarity and only exceptionally on clinical or epidemiological characteristics.
Structure (Morphology)
Infectious viruses (so-called virions) measure 20-300 nm in length or diameter and consist of: 1. strand of nucleic acid (DNA or RNA); 2. protein coat (core, capsid; capsid and nucleic acid together are referred to as the nucleocapsid); 3. complex virions are surrounded by a coat. Nucleocapsids mostly have simple geometrical forms. The viral coat partially originates from the host cell membrane, with glycoproteins from the virus itself protruding out of it (so-called spikes). These play an important role in the virulence of the virions and in the immunological reaction of the host.
1. Viruses are always cell parasites. The virion is first bound to certain receptor structures on the cell membrane of the host cell. 2. The virus coat either merges with the membrane of the host cell or the virus is taken up into the host cell by means of invaginations in the host cell, i.e. it is surrounded by the cell membrane and forced into the inside of the cell. The membrane is then dissolved by enzymes inside the cell. 3. Multiplication of the genetic material takes place in the host cell, using the host cell's molecular equipment. 4. The nucleic acids and polypeptides produced in the host cell are assembles to make infectious virions, which then leave the host cell. The coat of a virion is derived from the cell membrane of the host cell, after the virion has left the cell through a bud-like projection and constriction of the membrane.
Glossary entries: Roche and Walter de Gruyter, Berlin