16 Questions
What is the main component of the icosahedral protein coat of a virus?
Repeating units of protein (capsomers)
What is the characteristic shape of the helical protein coat of a virus?
Spiral or helical
What is the main proposal of the RNA world hypothesis?
A world filled with life based on RNA predated the current world of life based on DNA and protein
What is the characteristic symmetry of an icosahedron?
2, 3, and 5 fold axes of symmetry
What is the term for the whole protein coat of a virus?
Capsid
What is the theory that proposes viruses are subcellular, functional assemblies of macromolecules?
Cellular origins
What is the characteristic feature of the icosahedral protein coat of a virus?
It is made up of repeating units of protein
What is the criteria for an organism to be considered 'living'?
It must have order, reproduce, grow, utilise energy, respond to environment, maintain homeostasis, and adapt through evolution
What is the main function of the protective protein coat surrounding a viral genome?
To protect the viral genome from the host's immune system
What is a characteristic of the viral envelope?
It is a host-derived lipid from the extracellular membrane
What is the primary target organ of hepatitis viruses?
The liver
How are enteric viruses typically acquired?
Through ingestion of material contaminated with faeces
What is the size range of viruses?
10-400 nm
What is the role of the host cell in viral replication?
To provide the machinery for viral replication
What is the function of the spikes on the viral envelope?
To facilitate the attachment of the virus to host cells
What is the characteristic of arboviruses?
They infect insects that ingest vertebrate blood
Study Notes
Virus Structure
- Viruses have four main categories of structure: icosahedral, helical, viral envelopes, and complex symmetry.
- Icosahedral protein coat: made up of repeating units of protein (capsomers), surrounds nucleic acid and "core" protein, and may have associated proteins (e.g. polymerase).
- Properties of an icosahedron: 12 vertices, 20 equilateral triangles, 2, 3, and 5 fold axes of symmetry.
Characteristics of Viruses
- Very small (10-400nm), with some up to 1µM.
- Not cells.
- A genome surrounded by a protective protein coat.
- Infectious.
- Dependent on a host cell to provide the machinery needed to reproduce.
- Intracellular parasites.
- Formed from the assembly of newly synthesized components made in a host cell.
Origins of Viruses
- Three theories: regressive evolution, cellular origins, and independent entities.
- Regressive evolution: viruses are degenerate life-forms that have lost many functions.
- Cellular origins: viruses are subcellular, functional assemblies of macromolecules that have escaped from cells.
- Independent entities: viruses evolved from self-replicating molecules in the "RNA world".
Classification of Viruses
- Respiratory viruses: replicate primarily in the respiratory tract, acquired by inhalation, and include orthomyxovirus, rhinovirus, and coronaviruses.
- Enteric viruses: replicate primarily in the intestinal tract, acquired by ingestion, and include rotavirus, calicivirus, and astrovirus.
- Arboviruses: infect insects that ingest vertebrate blood, replicate in the insect, and are transmitted by bite.
- Hepatitis viruses: principal target organ is the liver, and include hepatitis A, B, C, D, and E.
- Sexually transmitted viruses: include some herpesviruses, papillomaviruses, retroviruses, and hepatitis viruses that cause lesions in the genital tract or are transmitted during sexual activity.
RNA World Hypothesis
- Proposes that a world filled with life based on RNA predates the current world of life based on DNA and protein.
- Suggests that RNA was the primary molecule of life.
Learn about the different categories of virus structure, including icosahedral protein coats, and their properties. Discover the repeating units of protein, capsomers, and the axes of symmetry.
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