Answer:
Step-by-step explanation:
A virus is an infectious particle that reproduces by attacking a host cell. A virus may be a DNA or RNA genome. Retrovirus is a virus whose genome consists of RNA. Genome is placed inside a protein named capsid. In certain types of viruses, there is an envelope membrane. A virion is a single individual particle of a virus. Thus, the virus depends on the host cell in order to live and reproduce. In the case when the virus is outside the host cell, the virus is metabolically inactive. In the case when it is in contact with the host cell, a virus translocates its genetic material into the cell host. In that manner, a virus may take over the cells' functions.
Thus, an infected host cell starts to produce the virus and its proteins. In certain cases, a virus may rest and cause no protein production, thus, remaining in the lysogenic phase. In case a virus is dominant and active, that is called the lytic phase. In the lytic phase, the viruses are produced. The replication of virus has six stages. They are termed as attachment, penetration, uncoating, replication, assembly and release. In the stage of attachment and penetration, the virus is attacking the host cell and transferring its genetic material into it. The bacteriophage is a virus that infects prokaryotic cells.
Another process may occur in the contact of virus and the host cells that are called the transfer of genetic material between different species of the host. Thus, genetic engineering may happen, as well. Genetic engineering happens when the virus incorporates certain genetic material from its host and thus, replicate afterwards (transduction).
In humans, a virus may cause a large number of diseases such as: smallpox, the common cold (rhinovirus), shingles, herpes infections, polio, rabies, chickenpox, Ebola, AIDS etc. Prions are viral, infectious particles that are entirely made up of the protein and have no nucleic acid. Prions are highly heat resistant and may cause animal diseases that affect nervous tissue (bovine spongiform encephalitis, scrapies, kuru and Creutzfeldt-Jakob diseases in humans).