Viruses: Features & Characteristics

Question 1

Define Microbiology

Answer 1

The study of micro-organisms, including bacteria, fungi, viruses and pathogenic protozoa, and the diseases they cause.

Question 2

Early theories;

• Cell Theory
• Miasma Theory
• Germ Theory

Define biogenesis

Answer 2

Cell Theory: all living things are composed of cells (not entirely true)

Miasma Theory: Diseases are caused by miasma (poisonous vapor or mist filled w/ decomposing matter)

Germ Theory: Micro-organisms are cause of many diseases (Cornerstone of modern medicine)

Biogenesis: living cells can only arise from pre-existing cells

Question 3

Koch’s 4 Postulates (Modified for Viruses)

-Criteria used to test whether a disease is caused by a micro-organism (Virus in this case)

Answer 3

As viruses are obligate parasites of cellular organisms;

1. The virus must be present in every case of the disease
2. It must be isolated by cultivation in an appropriate tissue
3. Specific disease must be reproduced when the cultivated virus is reintroduced into a susceptible host
4. The virus must be recoverable once again from the experimentally infected host.

Question 4

Characteristics of Viruses

Answer 4

• Small (generally < 250nm)
• Filterable (filtering infected material doesn’t rid virus)
• Lack cellular organelles - need living cells to replicate
• Are particles
• Has a RNA or DNA genome enclosed w/in protein coat (capsid)
  - genome may be ss or ds, linear or circular, positive sense or negative sense

n.b. Nucleic acid of some viruses may be infectious if inserted into host cell

Question 5

Define Virus

Answer 5

Viruses are entities whose genomes are elements of nucleic acid that replicate inside living cells using the cellular synthetic machinery and causing the synthesis of specialized elements that can transfer the viral genomes to other cells.

Question 6

3 main morphological configurations

Answer 6

1. Isometric Viruses (may or may not be surrounded by envelope)
2. Tubular nucleocapsids inside lipoprotein envelopes (Helical Viruses)
3. Complex Viruses

Question 7

Features of Isometric Viruses

Answer 7

• Always have an icosahedral capsid (20 equilateral triangular faces, 30 edges, 12 vertices)
• May or may not be enclosed in lipoprotein (derived from cellular membranes of the host)

e.g. of enclosed: Herpesvirus
non-enclosed: Adenoviruses

Question 8

Features of Tubular nucleocapsids inside lipoprotein envelopes (aka Helical Viruses)

Answer 8

• only seen in viruses w/ RNA genome (e.g. influenza virus)
• protein molecules arranged in helical manner -> protects RNA genomes from nucleases (enzymes)
• Almost all have negative sense, ss RNA genomes (except family Coronaviridae)

Question 9

Features of Complex Viruses

Answer 9

• Same essential characteristics as others, though has nucleocapsid surrounded by additional protein coat
• has lateral bodies of unknown function

e.g. Poxvirus

Question 10

Multifunctional role of Lipoprotein (3)

Answer 10

1. Has proteins w/ import. role in infectious process - i.e. attachment of virus to cell
2. Acts as a coat & protects nucleocapsid
3. Derived (DO NOT ENCODE LIPIDS) from membrane of host cell during maturation of virus (means this differs depending on where the virus matured).

Question 11

Structural and non-structural proteins in Viruses

Answer 11

Structural Proteins: may contribute to capsid or form part of lipoprotein envelope.
-may be involved w/ virus attachment
Non-structural Proteins: May have enzymatic activity or other function required for virus replication

-Proteins are a major component of viruses

Question 12

Define; -

• Virion
• Capsid
• Capsomer
• Nucleocapsid
• Envelope
• Isometric Viruses

Answer 12

Virion: “virus particle”
Capsid: the protein coat
Capsomer: morphological units visible on the surface of the capsid - make up the capsid’s structure
Nucleocapsid: where capsid (protein coat) directly encloses the viral nuclei acid.
Envelope: lipoprotein membrane surrounding the (nucleo) capside
Isometric viruses: Viruses w/ icosahedral capsids

Question 13

Taxonomy vs. nomenclature

Answer 13

Taxonomy: The orderly classification of organisms into appropriate categories (taxa)

Nomenclature: a classified system of technical names. The application of agreed names to taxomonic groups and to members w/in each group.

-current classification schemes based on combo of phenotypic and genotypic characteristics
RESULT: groups of viruses w/ common biological properties

Question 14

Official Hierarchy suffix (Order to Species)

Answer 14

Order:                 -virales
Family:                -viridae
Sub-Family:        -virinae
Genus:                -virus
Species:              none