Viruses

Flashcards reviewing key vocabulary and concepts about viruses from Campbell Biology, 12th Edition, Chapter 19.

Virus

An infectious particle consisting of genes packaged in a protein coat. They are simpler in structure than prokaryotic cells, can cause various diseases, and cannot reproduce or carry out metabolism outside a host cell.

Tobacco Mosaic Virus (TMV)

An infectious particle that stunts the growth of tobacco plants and gives their leaves a mosaic coloration; was crystallized by Wendell Stanley in 1935.

Viral Genome

Can consist of either double- or single-stranded DNA or RNA; classified as DNA or RNA viruses, with genomes having between 3 and 2,000 genes.

Capsid

The protein shell that encloses the viral genome; built from protein subunits called capsomeres and can have helical or icosahedral structures.

Viral Envelope

Derived from membranes of host cells, surrounds the capsids of some viruses (like influenza) and contains a combination of viral and host cell molecules, aiding in host infection.

Bacteriophages (Phages)

Viruses that infect bacteria; consists of an elongated capsid head enclosing DNA and a protein tail piece for host attachment and DNA injection.

Obligate Intracellular Parasites

Viruses that can replicate only within a host cell; each virus has a specific host range, which is the limited number of host species it can infect.

Lytic Cycle

A phage replicative cycle that results in the death of the host cell by producing new phages and lysing (breaking open) the cell wall; phages that reproduce only this way are called virulent phages.

Lysogenic Cycle

Replicates the phage genome without destroying the host; the viral DNA is incorporated into the host cell’s chromosome, and phages using both cycles are called temperate phages.

Prophage

The integrated viral DNA in the lysogenic cycle; copied during host cell division and passed to daughter cells; can be triggered by an environmental signal to switch to the lytic mode.

Restriction Enzymes

Cellular enzymes in bacteria that cut up foreign DNA; the bacterium's own DNA is protected by methylation.

CRISPR-Cas System

A defense system used by bacteria and archaea against viral infections; based on sequences called clustered regularly interspaced short palindromic repeats (CRISPRs).

Viral Glycoproteins

Proteins on the viral envelope that bind to specific receptor molecules on the surface of a host cell to facilitate entry.

Retroviruses

Use reverse transcriptase to copy their RNA genome into DNA; HIV is a retrovirus that causes AIDS.

Provirus

Viral DNA that is integrated into the host genome in retroviruses; remains a permanent resident of the host cell.

Emerging Viruses

Viruses that suddenly become apparent, either through mutation, spread from small populations, or transmission from other animals.

Hemorrhagic Fever

A severe and often fatal illness caused by viruses like the Ebola virus.

Pandemic

A global epidemic, such as the H1N1 flu in 2009.

Horizontal Transmission

A method by which plant viruses spread disease by entering through damaged cell walls.

Vertical Transmission

A method by which plant viruses spread disease by inheriting the virus from a parent.

Prions

Infectious proteins that cause degenerative brain diseases in animals by converting normal proteins into misfolded versions. Diseases include scrapie, mad cow disease, and Creutzfeldt-Jakob disease.

Vaccine

A harmless derivative of a pathogen that stimulates the immune system to mount defenses against the harmful pathogen.