Characterizing and Classifying Viruses, Viroids, and Prions

Virus

Minuscule, acellular infectious agents with DNA or RNA.

Infectious Agents

Pathogens causing diseases in various organisms.

Virion

Extracellular state of a virus, includes capsid.

Capsid

Protein coat surrounding viral nucleic acid.

Nucleocapsid

Combination of nucleic acid and capsid.

Phospholipid Envelope

Outer layer providing protection and host recognition.

Intracellular State

Virus exists as nucleic acid after capsid removal.

Genetic Material

Variety in viral genomes; DNA or RNA only.

dsDNA

Double-stranded DNA, one type of viral genome.

ssDNA

Single-stranded DNA, another type of viral genome.

dsRNA

Double-stranded RNA, a viral genome type.

ssRNA

Single-stranded RNA, a type of viral genome.

Host Specificity

Viruses infect specific host cells via surface proteins.

Bacteriophage

Virus that specifically infects bacteria.

Plant Viruses

Viruses infecting food crops through cell wall abrasions.

Fungal Viruses

Understudied viruses, lack extracellular state.

Capsomere

Protein subunits composing the capsid.

Capsid Morphology

Shape and structure of viral capsids.

Viral Envelope Composition

Phospholipid bilayer and proteins from host cell.

Glycoproteins

Viral proteins aiding in host recognition.

Generalist Viruses

Infect multiple cell types across various hosts.

Viral Replication

Process of virus using host's metabolic pathways.

Extracellular State

Virus outside host; can infect new cells.

Intracellular State

Virus inside host; utilizes host machinery.

Viral Genome Size

Much smaller than cellular genomes.

Viral Infection Mechanism

Involves attachment, entry, replication, and release.

Viral Diseases

Cause significant health issues in industrialized nations.

Viral Classification

Based on genetic material and host specificity.

Glycoproteins

Proteins on virus surface aiding in attachment.

Helical capsid

Cylindrical structure enclosing viral genome.

Matrix protein

Protein layer between capsid and envelope.

Envelope

Lipid membrane surrounding some viruses.

Enveloped virus

Virus with a lipid membrane coating.

International Committee on Taxonomy of Viruses

Body that classifies viruses based on characteristics.

Virus classification criteria

Based on nucleic acid, envelope, shape, size.

Lytic replication

Viral replication leading to host cell death.

Stages of lytic cycle

Attachment, Entry, Synthesis, Assembly, Release.

Attachment stage

Virus binds to host cell receptors.

Entry stage

Virus penetrates host cell membrane.

Synthesis stage

Host cell machinery produces viral components.

Assembly stage

New virions are formed from viral components.

Release stage

New virions exit host cell, causing lysis.

Lysogeny

Modified viral replication cycle without immediate lysis.

Temperate phages

Phages that can enter lysogenic cycle.

Prophages

Inactive phages integrated into host chromosome.

Lysogenic conversion

Phenotypic change in bacteria due to prophages.

Replication of animal viruses

Similar to bacteriophages with key differences.

Animal virus attachment

Chemical attraction between viral proteins and receptors.

Glycoprotein spikes

Molecules facilitating attachment of animal viruses.

Entry mechanisms of animal viruses

Direct penetration, membrane fusion, endocytosis.

Direct penetration

Virus injects genome directly into host cell.

Membrane fusion

Virus envelope merges with host cell membrane.

Endocytosis

Host cell engulfs virus, forming a vesicle.

Uncoating

Process of removing viral capsid after entry.

Synthesis of DNA viruses

Often occurs in the nucleus of host cells.

Synthesis of RNA viruses

Typically occurs in the cytoplasm of host cells.

mRNA synthesis

Process of creating messenger RNA from DNA.

Nucleic acid replication template

Strand used to synthesize new nucleic acids.

Viral Replication

Process by which viruses reproduce within host cells.

Animal Viruses

Viruses that specifically infect animal cells.

dsDNA Viruses

Double-stranded DNA viruses replicating like cellular DNA.

Nucleus

Location where viral genome is replicated for dsDNA.

Cytoplasm

Site where viral proteins are synthesized.

Poxvirus

Exception; replicates in the cytoplasm, not nucleus.

Hepatitis B Virus

Uses RNA intermediary to replicate DNA.

ssDNA Viruses

Single-stranded DNA viruses not utilized by host cells.

Parvoviruses

Type of virus with ssDNA genomes.

Complementary DNA Strand

Formed by host enzymes to replicate ssDNA.

dsRNA Virus

Double-stranded RNA virus involved in viral replication.

Positive-sense ssRNA Virus

Acts as mRNA for protein synthesis.

Negative-sense ssRNA Virus

Requires complementary RNA for translation.

Retroviruses

Use DNA intermediary for genome production.

Viral Reverse Transcriptase

Enzyme that transcribes RNA into DNA in retroviruses.

Viral Assembly

Process where new virions are formed.

Budding

Release method for enveloped viruses from host cells.

Exocytosis

Release method for naked viruses.

Latency

Dormant state of viruses in host cells.

Latent Viruses

Viruses that remain inactive within host cells.

Proviruses

Viruses integrated into host DNA permanently.

Neoplasia

Uncontrolled cell division leading to tumor formation.

Tumor

Mass of neoplastic cells in multicellular organisms.

Benign Tumors

Non-cancerous growths that do not spread.

Malignant Tumors

Cancerous growths that invade surrounding tissues.

Metastasis

Process of tumor cells spreading to other body parts.

Oncogenes

Genes that promote cell division and can cause cancer.

Environmental Carcinogens

Factors like UV light and radiation that activate oncogenes.

Oncogenes

Genes that promote cancer development.

Viruses in Cancer

Viruses cause 20-25% of human cancers.

Tumor Repression

Mechanisms that prevent tumor formation.

Burkitt's Lymphoma

A type of cancer linked to Epstein-Barr virus.

Hodgkin's Disease

Cancer of the lymphatic system.

Kaposi's Sarcoma

Cancer associated with HIV infection.

Cervical Cancer

Cancer often caused by human papillomavirus (HPV).

Culturing Viruses

Viruses require host cells for growth.

Plaque Assay

Method to estimate phage numbers via plaques.

Embryonated Eggs

Used for culturing viruses; inexpensive and large.

Diploid Cell Cultures

Cell cultures with a limited lifespan.

Continuous Cell Cultures

Cell cultures that can grow indefinitely.

Viroids

Infectious RNA particles affecting plants.

Prions

Infectious proteins causing neurodegenerative diseases.