exam 3 part 3

Significance of Viruses

• Most abundant “life form” on planet
• All living organisms are infected by viruses
• Viruses are an important part of global nutrient cycling
• Control dynamics of organisms
• Outnumber bacteria in the environment by 10 to 100 fold
• Especially prominent in aquatic ecosystems
  • Marine
  • Freshwater
• May be equally abundant in soil

Term “Virus”

• Generally applied
• Latin for “poison or poisonous slime”
• In early medical literature for any infectious disease
• Viruses were referred to as “Filterable Agents”
  • Could not be proved with Koch’s Postulates
• Later Term “Virus” Restricted to these Filterable agents
  • Bacteria could be seen and Koch’s Postulates applied, not so with virus

Viruses

• General Description
  • Virion - extracellular small particle containing a nucleic acid and surrounded by protein (aka virus particle)
  • Obligate Intracellular pathogen
  • Virus replication
    • New nucleic acid
    • New protein coats
    • Known as viral infection
  • Host is cell in which virus can replicate

Virus Definition

• Small infectious particles
• Covering on outside
  • Capsid
  • (Sometimes with envelope)
• Central Core
  • Genetic Material
  • (sometimes with proteins or enzymes)

Principles of Virus Taxonomy

• Lack of information on origin and evolutionary history makes viral classification difficult
• A uniform classification system was developed in 1971 by the International Committee for Taxonomy of Viruses (ICTV)
  • In most current report described ~2,000 viruses
  • Classification based on numerous characteristics
    • Most important – nature of genome

Viral Genomes, Baltimore Classification

• Baltimore Classification scheme classifies viruses based on:
  • Type of nucleic acid (DNA or RNA)
  • Presence or absence of a strand (single or double stranded)
  • The way the nucleic acid is transcribed to mRNA

Viral Taxonomy

• Family names end in -viridae.
• Genus names end in -virus.
• Viral species: A group of viruses sharing similar genetic information and ecological niche (host). Common names are used for species.
• Subspecies are designated by a number.
• Viral Taxonomy Examples
  • Herpesviridae
    • Herpesvirus - Human herpesvirus HHV-1, HHV-2, HHV-3
  • Retroviridae (Family)
    • Lentivirus (Genus)
    • Human immunodeficiency virus HIV-1, HIV-2
  • Coronaviridae
    • Betacoronavirus
    • SARS coronavirus 2

Basic Virus Structure

Viral Structure

• Capsid
  • Coat, shell
  • Made up of protein subunits called capsomeres
  • Self-assemble into capsid
    • Helical
    • Polygonal (icosahedron, 20 sided)
    • Filamentous
    • Complex

Virus Capsid

• Protects
  • Surrounds genome of virus
• Transport
  • Has receptor Proteins often “spikes”
  • Binds to host
• Deliver
  • Helps eject viral genome
    • Especially in complex viruses

Viral Structure (cont)

• Envelope
  • Membranous structure surrounds capsid
  • Viral envelope is a lipid bilayer embedded with glycoproteins
  • Often this membrane is derived from the host cell membrane as virus leaves the cell.
  • Plays an important role in host recognition or specificity

Tobacco Mosaic Virus

• Simple RNA Virus
• Virion
  • Helical cylinder
  • Protein Capsid
  • Capsid made up of Capsomeres
• Infects Solanaceous plants such as tobacco and tomato

Human Papilloma Virus

• Icosohedral

Ebola Virus

• Curvilinear morphologic features

Virus types

• Simple viruses - capsule and genetic material
• Complex - virus has many appendages
  • Many are Bacteriophage
  • Multiple parts that must be assembled to allow it become infectious

Complex Viruses

• Multiple parts, must assemble before becoming infectious
• Many Bacteriophages are complex viruses

Viruses Types

• Naked or Enveloped
• Capsids
  • Helical or filamentous
    • Rabies and Ebola
  • Polyhedral
    • Adenovirus and Polio Virus
    • Influenza or herpes virus
• Complex
  • Bacteriophage

Summarize

• The basic structure of a virus includes a capsid, genome, and sometimes an envelope.
• Capsids are made of protein subunits called capsomeres, and can have different structures, such as helical or icosahedral.
• The genome can be made of DNA or RNA, and can be single or double stranded.
• The envelope is a membrane that surrounds the capsid and is derived from the host cell membrane.
• Simple viruses have a capsule and genetic material, while complex viruses have many appendages and require assembly before becoming infectious.

Obligate Intracellular Parasite

• Viruses must be grown in living cells.

Explore the crucial roles that viruses play in various ecosystems, including their abundance and impact on nutrient cycling. Understand the evolution of the term 'virus' and its implications in microbiology. This quiz covers essential characteristics and functions of viruses, emphasizing their prominence in both aquatic and terrestrial environments.