Virus Classification Overview

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary basis for the Baltimore classification of viruses?

Host organism of viruses

Structure of viruses

Viral replication mechanisms

Messenger RNA synthesis (correct)

Which group in the Baltimore classification contains viruses with a DNA intermediate in their life cycle?

Group VI (correct)

Group I

Group II

Group IV

How many groups are in the Baltimore classification scheme for viruses?

Seven groups (correct)

Eight groups

Five groups

Six groups

What is the role of the International Committee on Taxonomy of Viruses (ICTV)?

To establish a universal taxonomic scheme for all viruses Signup and view all the answers

Which type of viruses is classified under Group V of the Baltimore classification?

Single-stranded RNA viruses (Negative sense) Signup and view all the answers

What is the primary structural feature that distinguishes viruses classified under the LHT system?

Capsid structure Signup and view all the answers

Which of the following classifications focuses specifically on the structural properties of viruses?

ICTV Classification Signup and view all the answers

In the Baltimore classification, which group includes single-stranded DNA viruses?

Group II Signup and view all the answers

How are the classes further divided in the ICTV classification system?

Into orders, suborders, families, and genera Signup and view all the answers

Which group in the Baltimore classification contains double-stranded RNA viruses?

Group III Signup and view all the answers

What is the main distinction of viruses classified under Group VI in the Baltimore classification?

They have a DNA intermediate in their life cycle. Signup and view all the answers

Which of the following classification systems was finalized in 1966?

LHT System Classification Signup and view all the answers

Which group listed under the Baltimore classification includes viruses like Retroviridae?

Group VI Signup and view all the answers

What term refers to the complete virus with its structural components?

Virion Signup and view all the answers

Which component forms the spikes on the envelope of some viruses?

Peplomers Signup and view all the answers

What is the typical size range of viruses in the Hepadnaviridae family?

18-20 nm Signup and view all the answers

Which type of virus has capsomers that bond to six neighboring capsomers called hexons?

Adenovirus Signup and view all the answers

What principle explains how virions minimize free energy through capsomer organization?

Caspar-Klug principle Signup and view all the answers

What defines helical viruses, specifically regarding their physical structure?

Amplitude and pitch Signup and view all the answers

Regular icosahedra are formed when the triangulation number, P, is equal to which values?

1 or 3 Signup and view all the answers

During budding, what component forms the outer layer of enveloped virus particles?

Lipid bilayer Signup and view all the answers

Study Notes

Baltimore Classification of Viruses

The Baltimore classification system classifies viruses based on their genome structure and the method of mRNA synthesis.
Group II in the Baltimore classification contains viruses with a DNA intermediate in their life cycle.
The Baltimore classification system categorizes viruses into seven groups.
The International Committee on Taxonomy of Viruses (ICTV) is responsible for naming and classifying viruses.
Group V of the Baltimore classification encompasses retroviruses. These viruses use reverse transcriptase to generate DNA from their RNA genome.

Virus Classification and Properties

Holmes Classification: Divides viruses into three groups: Phaginae (infecting bacteria), Phytophaginae (infecting plants), and Zoophaginae (infecting animals).
LHT (Lwoff, Horne, and Tournier) System: Organizes viruses based on structural properties.
- Phylum: Vira
- Subphyla: Deoxyvira (DNA viruses) and Ribovira (RNA viruses)
- Classes: Deoxybinala, Deoxyhelica, Deoxycubica, Ribocubica, and Ribohelica
ICTV (International Committee on Taxonomy of Viruses) System: A hierarchical classification, focusing on structural properties and viral lineages.
- Orders: "…virales"
- Suborders: "…viridales"
- Families: "…viridae"
- Subfamilies: "…virinae"
- Genera: "…virus"
- Subgenera: "…virus"
Baltimore Classification: Groups viruses based on their mRNA synthesis strategy.
- Group I: Double-stranded DNA viruses (e.g., Herperviridae, Iridoviridae, Poxviridae, Adenoviridae, Asfaviridae, Papillomaviridae)
- Group II: Single-stranded DNA viruses (e.g., Parvoviridae, Circoviridae)
- Group III: Double-stranded RNA viruses (e.g., Birnaviridae, Reoviridae)
- Group IV: Single-stranded RNA viruses (Positive sense) (e.g., Arteriviridae, Coronaviridae, Picornaviridae, Flaviviridae, Togaviridae, Astroviridae)
- Group V: Single-stranded RNA viruses (Negative sense) (e.g., Arenaviridae, Bunyaviridae, Orthomyxoviridae, Paramyxoviridae, Bornaviridae, Rhabdoviridae, Filoviridae)
- Group VI: Single-stranded RNA viruses with a DNA intermediate (e.g., Retroviridae)
- Group VII: Double-stranded DNA viruses with an RNA intermediate (e.g., Hepadnaviridae)

Virus Structure

Size: Varies drastically, ranging from 18-20 nm (Parvovirus) to 130-375 nm (Poxvirus). Some filamentous Filoviruses can reach up to 14,000 nm.
Capsid: The protein coat of a virus.
Nucleocapsid: The capsid enclosing the nucleic acid genome.
Capsomers: Structural subunits of the capsid.
Envelope: A lipid bilayer membrane surrounding some viruses outside of the capsid.
Peplomers: Spikes found on the envelope of some viruses.
Viroids: Complete viral particles with all structural components.
Virus Symmetry: The shape of the capsid/nucleocapsid.
- Icosahedral Viruses: Have a polyhedral shape with 20 equilateral triangular faces.
  - Hexons: Capsomers on the faces of icosahedral viruses, bonding to six neighbors.
  - Pentons: Capsomers at the vertices of icosahedral viruses, bonding to five neighbors.
- Helical Viruses: Have a cylindrical or rod-like shape.
  - Pitch: The distance covered by each complete turn of the helix.
  - Example: Tobacco mosaic virus (TMV) has a pitch of 2.28 Å.
- Complex Viruses: Exhibit more intricate structures, combining elements from both icosahedral and helical symmetries.
  - Example: Rhabdovirus particles (e.g., vesicular stomatitis virus).
Caspar-Klug Principle: Explains how capsomers are organized quasi-equivalently to minimize free energy during virion formation.
Triangulation number (T): A mathematical formula used to describe the complexity of icosahedral structures.
- Formula: T=a2+ab+b2 where a and b are integers.
- Regular icosahedra: T=1 or 3.
Enveloped Viruses: Acquire their envelopes by budding through a host cell membrane, acquiring a lipid bilayer derived from the host cell.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Explore the classification of viruses through two major systems: the structure-based classification by the ICTV and the Baltimore classification based on mRNA synthesis. Learn about the different groups within the Baltimore classification and the criteria used to categorize various viruses based on their genetic material.