Microbiology: Biological Viruses Structure and Life Cycle

This set of flashcards covers vocabulary related to the structure, replication cycles, and medical significance of viruses and prions based on microbiology lecture notes.

Obligate intracellular parasites

A description of viruses meaning they can replicate only inside a living host cell and can infect various organisms.

Capsid

The protein shell that surrounds the nucleic acid core of a virus particle.

Nucleocapsid

A structure consisting of the viral capsid together with the nucleic acid it encloses.

Naked viruses

Viruses that consist only of a nucleocapsid and lack an external envelope.

Envelope

The external covering of a nucleocapsid, usually acquired from a modified piece of the host cell membrane during budding.

Spikes

Glycoproteins that project from the nucleocapsid or envelope, allowing viruses to dock with specific host cell receptors.

Capsomeres

The individual protein subunits that assemble to form the viral capsid.

Icosahedral

A specific viral shape consisting of triangular faces.

Reverse transcriptase

An enzyme used by some viruses, such as HIV, to synthesize DNA from an RNA template.

Adsorption

The first step of the animal virus replication cycle involving the attachment of the virus to its specific host cell.

Host range

The specific spectrum of hosts that a particular virus is capable of infecting.

Viral specificity

The specific kinds of cells or tissues a virus can infect within a certain host species.

Endocytosis

A penetration mechanism where the entire virus is engulfed by the host cell and enclosed within a vacuole.

Membrane Fusion

A penetration mechanism used only by enveloped viruses where the viral envelope merges directly with the host cell membrane.

Uncoating

The step in which viral DNA or RNA is released into the cytoplasm after host cell enzymes dissolve the envelope and capsid.

Synthesis

The stage of the lifecycle where viral genetic material is replicated and new viral proteins are produced.

Assembly

The process of putting together all viral components to create mature viruses.

Budding

A release method where the nucleocapsid binds to the host membrane and pinches off, allowing the virus to take a piece of the membrane as an envelope.

Cytopathic Effects (CPEs)

Virus-induced damage to the host cell that alters its microscopic appearance, such as changes in shape, size, or intracellular structures.

Syncytia

The fusion of multiple host cells into single large cells containing multiple nuclei as a result of viral infection.

Provirus

A viral state where the virus incorporates its genetic material into the DNA of the host, such as in chronic HIV infections.

Oncoviruses

Mammalian viruses capable of initiating tumors and causing approximately $13\%$ of human cancers.

Lysozyme

An enzyme present in the tail fibers of bacteriophages that weakens the bacterial cell wall to allow for DNA injection.

Lysogenic conversion

The process by which a bacterium acquires a new trait, such as toxin production, from its temperate phage.

Prions

Infectious proteins that cause diseases like Creutzfeldt-Jakob by building up in cells and creating sponge-like lesions in the brain.

What are viruses?

Viruses are known to infect many cell types (animal, bacterial, fungal, protozoan, plant etc.). They lack metabolic machinery and must infect a host cell to reprogram its metabolic functions to produce more viruses.

Cells vs. Viruses

Cells contain DNA and RNA and can grow and divide independently, whereas viruses have either DNA or RNA (never both) and depend on a living host cell's metabolic machinery for survival.

Components of a Virus

1. Nucleic acid core - The genetic material of the virus. Contains DNA or RNA.

2. Capsid - Composed of capsomere proteins that encase the nucleic acid core, protecting the genetic material and contributing to the virus's shape.

3. Envelope - An optional layer made of phospholipids and proteins, acquired from the host cell's membrane during budding.

4. Spikes - Glycoproteins on the envelope involved in binding the virus to host cell receptors.

Animal Virus Replication Cycle

1. Adsorption - Virus binds to the host's cell membrane receptors via spikes.

2. Penetration - Virus enters the host cell via endocytosis or membrane fusion (for enveloped viruses).

3. Uncoating - Viral genetic material is released into the cytoplasm.

4. Synthesis - Host cell is manipulated to produce viral DNA/RNA and proteins.

5. Assembly - Viral components are assembled into mature viruses.

6. Release - Naked viruses are released via lysis; enveloped viruses are released via budding.

Cytopathic Effects (CPEs)

Virus-induced damage to the cell that alters its microscopic appearance.

Proviruses

Viruses like Varicella zoster virus establish a latent relationship with the host cell, leading to recurrent infections.

Oncoviruses

Mammalian viruses capable of initiating tumors and causing cancer.

Bacteriophages

Viruses that infect and potentially kill bacteria, having either lytic or lysogenic life cycles.

Lytic life cycle

A cycle that leads to the destruction of the bacterium with the release of new bacteriophages. Includes stages: Adsorption, Penetration, Synthesis, Assembly, and Release.

Lysogenic cycle

Where bacteriophage DNA incorporates into the bacterial genome, allowing the bacterium to gain new traits, such as toxin production or antibiotic resistance.

In vivo research

Research done within a living organism, such as live animal inoculation or bird embryo inoculation.

In vitro research

Research done outside a living organism, often in a lab environment, using cell cultures.

Plaque assay

A method to observe the degeneration and lysis of infected cells in cell culture.

Misfolded prion proteins

Infectious proteins that can induce other proteins to misfold in the brain, leading to diseases like Creutzfeldt-Jakob Disease (CJD).

Spongiform encephalopathies

Brain diseases caused by prions leading to spongy degeneration of neurons.