Q.11 Viral capsids are made up of morphological subunits called capsomeres. One of the common capsomeres is icosahedral. The icosahedron is a regular polyhedron with
The correct answer is (B) 20 triangular facets and 12 vertices. A regular icosahedron, commonly used in viral capsids, features exactly 20 equilateral triangular faces and 12 vertices, as confirmed by geometric properties of Platonic solids.
Option Analysis
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(A) 16 triangular facets and 12 vertices: Incorrect, as no regular polyhedron matches 16 faces; icosahedrons have 20 faces.
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(B) 20 triangular facets and 12 vertices: Correct. This matches the icosahedron’s structure with 20 faces, 12 vertices, and 30 edges (Euler’s formula: V – E + F = 2).
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(C) 16 triangular facets and 16 vertices: Incorrect; 16 faces do not form a regular icosahedron, and vertex count mismatches.
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(D) 20 triangular facets and 16 vertices: Incorrect; icosahedrons always have 12 vertices where five triangles meet.
Viral Capsid Context
Viral capsids consist of capsomeres forming icosahedral symmetry for efficient genome enclosure. This structure provides 20 triangular faces meeting at 12 vertices, enabling stable assembly via pentamers (at vertices) and hexamers (on faces).
Introduction to Icosahedron Viral Capsids
Icosahedron viral capsids represent a key symmetry in virology, where capsomeres—morphological subunits—assemble into a regular polyhedron featuring 20 triangular facets and 12 vertices. This structure optimizes stability and genome protection in viruses like adenoviruses. Understanding icosahedron viral capsids capsomeres aids CSIR NET Life Sciences preparation.
Properties of Regular Icosahedron
A regular icosahedron, one of five Platonic solids, contains 20 equilateral triangular faces (facets), 12 vertices, and 30 edges. Five faces meet at each vertex, verified by Euler’s formula (12 – 30 + 20 = 2). No other regular polyhedron has 16 faces, eliminating common distractors.
Role in Viral Capsids
Capsomeres in icosahedron viral capsids include 12 pentamers at vertices and variable hexamers on faces, following quasi-equivalence theory. This enables efficient self-assembly, enclosing nucleic acids in a near-spherical shell. Examples include poliovirus and herpesviruses.
CSIR NET Exam Insights
CSIR NET questions on icosahedron viral capsids capsomeres test Platonic solid properties. Option (B) is standard: 20 triangular facets and 12 vertices. Misoptions like 16 facets confuse with other polyhedra. Practice verifies via geometry basics.
