Introduction to Virology: Characteristics, Classification, and Life Cycles

Comprehensive vocabulary flashcards covering viral structure, classification, bacteriophage replication cycles, bacterial defense mechanisms, and animal virus infection cycles based on lecture notes.

Virus

Infectious agents, not organisms, consisting of genetic information (DNA or RNA) contained within a protective protein coat; they are obligate intracellular parasites with no metabolism, replication, or motility of their own.

Bacteriophages (phages)

Viruses that specifically infect prokaryotes.

$$10^{31}$$

The estimated number of viruses on the planet, most of which infect prokaryotes.

Virion

An infectious virus particle containing nucleic acid inside a protein coat and, optionally, a lipid membrane.

Capsid

The protein coat of a virus that protects the nucleic acids and is composed of identical subunits called capsomeres.

Nucleocapsid

The complex formed by the viral capsid plus the nucleic acids it contains.

Enveloped viruses

Viruses that possess a lipid bilayer envelope; they are more susceptible to drying and disinfectants because the envelope is required for attachment to the host.

Non-enveloped (naked) viruses

Viruses that lack a lipid envelope, making them more resistant to disinfectants.

Spikes

Protein components on many animal viruses that allow the virion to attach to specific receptor sites on host cells.

Icosahedral

One of the three general shapes of viruses, characterized as a $20$-faced polyhedron.

-viridae

The suffix used to designate virus families.

Lytic phages

Bacteriophages that always have a lytic life cycle, such as the T4 phage, which culminates in the lysis of the host cell.

Temperate phages

Bacteriophages, such as the Lambda ($\lambda$) phage, that have the option of both a lytic life cycle and a lysogenic life cycle.

Lysogen

A bacterial cell that is infected with a temperate phage and carries the viral DNA integrated into its genome.

Prophage

The viral DNA that is integrated into the host bacterial genome during a lysogenic infection.

Lysogenic Conversion

A change in the phenotype of a lysogen caused by prophage genes, such as the production of toxins or immunity to superinfection.

Plaque assays

A method used to count phage particles where zones of clearing (plaques) in a bacterial lawn represent single phages.

Titer

The concentration of phage in an original sample, determined by counting plaques in a plaque assay.

Restriction enzymes

Bacterial enzymes that recognize and cut short, specific DNA sequences; they degrade unmethylated phage DNA to prevent replication.

Modification enzymes

Bacterial enzymes that methylate host DNA sequences at restriction sites to protect them from being cut by the cell's own restriction enzymes.

CRISPR system

Clusters of Regularly Interspersed Short Palindromic Repeats that provide a record of past infections by inserting phage spacer DNA into the bacterial genome to target future phage genomes for destruction.

Tropism

The limitation of a virus to a specific range of hosts or cell types based on the requirement for specific host receptors.

Uncoating

The step in the animal virus infection cycle where the nucleic acid separates from the capsid.

Budding

The process of virus release where the nucleocapsid is extruded from the host cell, becoming coated with matrix proteins and a lipid envelope derived from the host's membrane.

Replicase (RNA-dependent RNA polymerase)

A virally encoded enzyme that lacks proofreading and is used by RNA viruses to synthesize RNA from an RNA template, leading to antigenic drift.

Reverse transcriptase (RNA-dependent DNA polymerase)

An enzyme encoded by retroviruses that makes DNA from an RNA template.

Antigenic drift

The result of genetic variations in RNA viruses caused by the lack of proofreading in replicase enzymes.