Virus Structure and Properties

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Questions and Answers

What is the main component of the icosahedral protein coat of a virus?

Repeating units of protein (capsomers) (correct)

Polymerase

Nucleic acid

Core protein

What is the characteristic shape of the helical protein coat of a virus?

Triangular

Spiral or helical (correct)

Pentagonal

Icosahedral

What is the main proposal of the RNA world hypothesis?

RNA was the first molecule to evolve on Earth

RNA is the simplest molecule to replicate

RNA is the most common molecule in the universe

A world filled with life based on RNA predated the current world of life based on DNA and protein (correct)

What is the characteristic symmetry of an icosahedron?

2, 3, and 5 fold axes of symmetry Signup and view all the answers

What is the term for the whole protein coat of a virus?

Capsid Signup and view all the answers

What is the theory that proposes viruses are subcellular, functional assemblies of macromolecules?

Cellular origins Signup and view all the answers

What is the characteristic feature of the icosahedral protein coat of a virus?

It is made up of repeating units of protein Signup and view all the answers

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 Signup and view all the answers

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 Signup and view all the answers

What is a characteristic of the viral envelope?

It is a host-derived lipid from the extracellular membrane Signup and view all the answers

What is the primary target organ of hepatitis viruses?

The liver Signup and view all the answers

How are enteric viruses typically acquired?

Through ingestion of material contaminated with faeces Signup and view all the answers

What is the size range of viruses?

10-400 nm Signup and view all the answers

What is the role of the host cell in viral replication?

To provide the machinery for viral replication Signup and view all the answers

What is the function of the spikes on the viral envelope?

To facilitate the attachment of the virus to host cells Signup and view all the answers

What is the characteristic of arboviruses?

They infect insects that ingest vertebrate blood Signup and view all the answers

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.

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Description

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.