Virology

Characteristics of life agreed upon by biologists

1. Composed of cells

2. Can reproduce

3. Regulate and metabolize energy

4. Responds to stimuli

5. Ability to grow

Definition of Virus

1. Mechanism of replication

2. Virus particles = virion. Composed of Nucleic acid genome and protein coat

Why are viruses not considered living?

Highjacks energy rather than gaining and consuming themselves. Relies on others to reproduce. Not composed of cells. Can not respond to stimuli by themselves.

Subunit (protein subunit)

Single, folded polypeptide chain

Structural unit (Asymmetric unit)

Unit from which capsids or nucleocapsids are built; may comprise one protein subunit or multiple different protein subunits

Capsid (Coat)

The protein shell surrounding the nucleic acid genome

Nucleocapsid (Core)

The nucleic acid-protein assembly packaged within the virion; used when this assembly is a discrete substructure of a particle

Envelope (Viral membrane)

The host cell-derived lipid bilayer carrying viral glycoproteins

Virion

The infectious virus particle

Icosahedral symmetry

Helical Symmetry

Triangulation number, T

Number of asymmetric units per face of the icosahedron constructed in this way

Principle of triangulation

The formation of large capsids with icosahedral symmetry

Virus particles purpose

To ensure protection and delivery of the genome to host cell

Protein-protein interaction

Dictates construction of capsids from a small number of subunits

Primary determine of capsid size

Number of subunits. More subunits = larger

Large icosahedral capsids contain

Dedicated stabilizing proteins or multiple protein shells that reinforce one another

Virus defined by 4 traits

1. Virion

2. encode at least 1 capsomere protein

3. Replicate by assembly

4. capacity to evolve

Virus particles can contain

Non structural components, including enzymes (I.e reverse transcriptase), small RNAs, and cellular macromolecules

Antiviral medications

interfere with viral enzymes not normally found within human cells

vaccines

provoke a protective immune response without making patient sick

Syncytia

large multinucleate eukaryotic cells caused by viruses

Cytopathic effects (CPEs)

cells display a variety of these that depend of specific host cell and virus. Including: round up, inclusion bodies, transform, and syncytia

Round Up

cells lose their shape becoming “spherical”, detach from growth surface and die

Spike Protein

protein that protrudes away from the surface of a virion and is typically used for attachment

Transform

cells become set on path to cancerous cells

Fluorescence microscopy

variation of high microscopy in which specific subcellar, cellular or viral features have been manipulated to make them ____

Light microscopy

can see up to 220 nm (0.22 um)

Inclusion bodies

abnormal internal structures that are visible when stained

Electron microscopy

<100um to 10nm

Mimivirus

gigantic nucleocytoplasmic large DNA virus. Enters ameba host via phagocytosis. Have some translation related genes.

Megavirus

gigantic nucleocytoplasmic large DNA virus. Has some translation related genes. Can be infected with their own virus.

LUCA

Last universal common ancestor

Virophage

Nucleocytoplasmic large DNA virus

An order of virus with a DNA genome. Some express genes/replicate in the cytoplasm and others in the nucleus.

Sattelite Virus

require co-infection with another virus to complete their replication cycle and spread. EX: AAV and adenovirus

Subviral entities

Simpler than viruses but exhibit behavior like them. Ex: Satellite virus, viroids, introns, transposons

Satellite Nucleic Acids

depend on a helper virus for replication, but do not encode a capsomer. Most are smaller than the genome of a satellite virus.

Satellite RNA

Viroids

RNA molecules with a secondary rod-shaped structure. Does not encode proteins. Infect plants through mechanical/physical damage and does not require encapsidation for transmission.

Transposons (transposable elements)

DNA sequences that can move from one place to another in a DNA genome. Similar to viruses as they can replicate at expense of their host. Proteins they encode are homologous to viral proteins.

Prions

Subviral protein with no genetic material

Introns

noncoding sequences within genes, have a functional role in gene expression as structure but without independent infectivity or replication

Subviral Entities

Simpler and smaller than viruses yet behave and spread in some ways like viruses. Lacks key components like a protein coat or independent replication.

Atomic force microscopy

<100um to .1nm (1 A)

Baltimore Classifictions

Sputnik

ICTV (International Committee on Taxonomy of Viruses

Bases classification on evolutionary relationships and genetic similarities between viruses

David Baltimore

Made classification scheme, Nobel prize for reverse transcriptase