Today I’m going to talk about: Virus (life science)
Virus (life science), infectious agent found in virtually all life
forms, including humans, animals, plants, fungi, and bacteria. Viruses
consist of genetic material DNA or RNA but not both surrounded by a
protective coating of protein, called a capsid, with or without an outer
lipid envelope. Viruses are between 20 and 100 times smaller than bacteria
and hence are too small to be seen by light microscopy. Viruses are not
considered free-living, since they cannot reproduce outside of a living
cell; they have evolved to transmit their genetic information from one cell
to another for the purpose of replication. Viral replication is often
carried out at the expense of the host: Diseases such as herpes, rabies,
influenza, some cancers, poliomyelitis, and yellow fever are of viral
origin. Of the estimated 1000 to 1500 types of viruses, approximately 250
cause disease in humans (over 100 of which cause the common cold), and 100
infect other animals. Because viruses are programmed to carry genetic
information into cells, they have been used to replace defective cellular
genes. Viruses are also being altered by genetic engineering to kill
selected cell populations, such as tumor cells. The use of genetically
engineered viruses for medical intervention is a relatively new field, and
none of these therapies is widely available.