Virus

A virus is a non-metabolizing infectious body of genetic information, either DNA or RNA, encased in a protein coat.

There is ambiguity in taxonomy as to whether these agents are living or not. They characteristically lack organelles, a cell membrane, cytoplasm, and the ability to respire. They are tiny compared to bacteria, and over 5000 varieties have been identified.

Viruses reproduce by means of the metabolic faculties of their host cell. Through the lytic process and the lysogenic cycle, viruses propagate their genetic information.

Lytic cycle
The first means of viral reproduction is the lytic cycle. The primary difference between it and the lysogenic cycle is the destruction of the host cell at the end of the process.

Attachment and entry

The virus attaches to the cell membrane and releases enzymes that weaken the interface. It injects its genetic material into the cell.

Replication

The cell's reproductive machinery creates copies of the virus. The organlles of the cell are dedicated to producing viral components instead of doing their intended job. The nucleotides in the host cell's DNA are used to replicate viral DNA.

Assembly

The viral components come together and form new viruses.

Release

The cell lyses (dissolution of the cell wall) and releases viruses into the open.

Lysogenic cycle
The second means of viral reproduction is the lysogenic cycle. It is characterized by the incorporation of viral DNA into the host cell's DNA. The symptoms of a viral infection reproducing via lysogenesis are not always apparent, since the viral DNA may not be processed until a later time, when the DNA will undergo the lytic cycle and release phages.

Attachment and entry

The virus attaches to the cell membrane and releases enzymes that weaken the interface. It injects its genetic material into the cell. If it injects RNA, the enzyme reverse transcriptase is used to convert it to DNA.

Incorporation

The genetic information is incorporated into the cell's DNA. The cell reproduces normally, spreading the viral genome.

Lytic cycle

Some external stimulus such as UV radiation will cause the cell to enter the lytic cycle, causing the virus to manifest itself and the host to eventually die.