Define Microbiology
The study of micro-organisms, including bacteria, fungi, viruses and pathogenic protozoa, and the diseases they cause.
Early theories;
- Cell Theory
- Miasma Theory
- Germ Theory
Define biogenesis
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
Koch’s 4 Postulates (Modified for Viruses)
-Criteria used to test whether a disease is caused by a micro-organism (Virus in this case)
As viruses are obligate parasites of cellular organisms;
- The virus must be present in every case of the disease
- It must be isolated by cultivation in an appropriate tissue
- Specific disease must be reproduced when the cultivated virus is reintroduced into a susceptible host
- The virus must be recoverable once again from the experimentally infected host.
Characteristics of Viruses
- 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
Define Virus
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.
3 main morphological configurations
- Isometric Viruses (may or may not be surrounded by envelope)
- Tubular nucleocapsids inside lipoprotein envelopes (Helical Viruses)
- Complex Viruses
Features of Isometric Viruses
- 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
Features of Tubular nucleocapsids inside lipoprotein envelopes (aka Helical Viruses)
- 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)
Features of Complex Viruses
- Same essential characteristics as others, though has nucleocapsid surrounded by additional protein coat
- has lateral bodies of unknown function
e.g. Poxvirus
Multifunctional role of Lipoprotein (3)
- Has proteins w/ import. role in infectious process - i.e. attachment of virus to cell
- Acts as a coat & protects nucleocapsid
- Derived (DO NOT ENCODE LIPIDS) from membrane of host cell during maturation of virus (means this differs depending on where the virus matured).
Structural and non-structural proteins in Viruses
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
Define; -
- Virion
- Capsid
- Capsomer
- Nucleocapsid
- Envelope
- Isometric Viruses
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
Taxonomy vs. nomenclature
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
Official Hierarchy suffix (Order to Species)
Order: -virales Family: -viridae Sub-Family: -virinae Genus: -virus Species: none
