Gene Viruses

Capsid

another name for the protein coat of viruses.

Envelope

a semi-gelatinous outer coating that some viruses possess in addition to their capsid and nucleic acid; the envelope is actually the remnants of the cell the original virus infected.

Obligate Intracellular Parasites

parasites that absolutely require other living host cells in order to perform their functions and survive (when outside of living cells, they are completely dormant and lifeless); viruses are good examples.

Viral Replication

“viral reproduction”; the virus takes over a host cell and forces that cell to produce more viruses.

Lytic Infection (=lytic cycle)

one of the two basic types of viral replication; the lytic cycle takes place in 5 orderly steps.

Attachment

process in which a virus attaches to a host cell's plasma membrane or cell wall with its capsid.

Infection

the virus injects its DNA or RNA into the host cell after breaking down the cell's plasma membrane.

Replication

process in which the viral DNA or RNA takes over the host cell by integrating itself into the host cell's genome at strategic locations; this forces the host cell to shut down and produce only new viral particles.

Assembly

process in which new viruses are assembled and put together properly within the host cell.

Burst

newly assembled viruses burst forth from host cell and begin to invade new cells; usually kills the host cell.

Burst Size

the actual number of viruses produced during one replication cycle; this number varies by viral species.

Burst Time

amount of time from attachment to burst; this varies by species, but averages 20-40 minutes.

Lysogenic Infection (=lysogenic cycle)

one of the two basic types of viral replication; it takes place in an orderly sequence of seven basic steps: attachment, infection, integration, induction, replication, assembly, and burst.

Integration

process in which the viral DNA integrates itself into the host cell's genome, but does not immediately take over the host cell; instead, the viral DNA remains dormant within the host cell for an indeterminate amount of time (it is even replicated along with the rest of the cell's genome in mitosis and meiosis)

Prophage

special name for viral DNA that remains dormant within a host cell’s genome following integration.

Induction

process in which something happens environmentally or internally (=biochemically) which activates the virus from the latent lysogenic state (prophage) and brings it into the active lytic state; the virus will now enter the replication phase and begin to take over the host cell.

Viroids

small pieces of RNA that are not protected by a capsid; also called “infectious RNA”, they cause several plant diseases.

Prions

small, short pieces of protein that are not protected by a capsid; also called “infectious proteins”, they cause a few disease of the human nervous system.