Transcript slide1_medical-virology-1

Medical Virology
Introduction
Dr. Sameer Naji, MB, BCh, PhD (UK)
Dean Assistant
Head of Basic Medical Sciences Dept.
Faculty of Medicine
The Hashemite University
General Properties of Viruses
 Viruses are the smallest infectious agents.
 Most forms of life – animals, plants and bacteria
– are susceptible to infection with appropriate
viruses.
 Properties that distinguish viruses from other
microorganisms.:
1. They are obligate intracellular parasites
2. They are inert (nucleoprotein ) filterable Agents
3. Small size: viruses are smaller than other organisms,
vary in size (diameter) from 10 nm - 300 nm.
4. Genome: either DNA or RNA. The nucleic acid is
encased in a protein shell, which may be surrounded
by a lipid – containing membrane. The entire
infectious unit is termed a virion.
5. Metabolically inert:
Viruses have no metabolic activity outside
susceptible host cells; they do not possess any
ribosomes or protein-synthesizing apparatus,
cannot make energy or proteins independent of a
host cell, therefore, they multiply only in living
cells.
On entry, the genome or nucleic acid is
transcribed into – or acts as – mRNA which then
directs the replication of new virus particles.
Virus vs. Cells
Property
Type of nucleic acid
Proteins
Lipoprotein membrane
Ribosomes
Mitochondria
Viruses
DNA or RNA
Few
Enveloped
present in
some viruses
Absent
Absent
Enzymes
Multiplication by binary fission
None or few
No
Cells
DNA and RNA
Many
Cell membrane
present in
all cells
Present
Present in
eukaryotic cells
Many
Yes (most cells)
Viruses are Ultramicroscopic
The size of viruses
Terms & Definitions in Virology:
 Capsid: the protein shell, or coat, that encloses
the nucleic acid genome.
 Capsomeres: morphologic units seen in the
electron microscope on the surface of icosahedral
virus particles. They represent clusters of
polypeptides.
 Defective virus: a virus particle that is
functionally deficient in some aspect of
replication.
-
Envelope: a lipid-containing membrane that
surrounds some virus particles. It is acquired
during viral maturation by a budding process
through a cellular
membrane.
- Nucleocapsid: the protein-nucleic acid complex
representing the packaged form of the viral
genome (capsid + genome).
-
Structural units: the basic protein building
blocks of coat.
- Subunit: a single folded viral polypeptide chain.
- Virion: the complete intact virus particle.
Sometimes it is identical with the
nucleocapsid (as in papillomaviruses).
In more complex virions (as herpesviruses),
this includes the nucleocapsid plus a
surrounding envelope.
Viral Structure - Overview
Nucleic acid
Nucleocapsid
Capsid
Envelope protein
Membrane protein
Spike protein
Viral envelope**
Schematic overview of the structure of animal viruses
** does not exist in all viruses
Naming viruses
• No taxa above Family (no kingdom, phylum, etc)
• Classified based on structures, size, nucleic acids, host
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•
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species, target cells.
20 families of animal viruses (7 DNA, 13 RNA)
Family name ends in – viridae
Subfamily ends in — virinae
Genus name ends in – virus
Species

–
–
–
–
–
Example
Family – Herpesviridae
Subfamily - Herpesvirinae
Genus – Simplex virus
Common name – herpes virus (Herpes simplex virus I (HSV-I)
Disease – fever blisters, cold sores
How are viruses named?
 Based on:
- the disease they cause
poliovirus, rabies virus
- the type of disease
murine leukemia virus
- geographic locations
Sendai virus, Coxsackie virus
- their discovers
Epstein-Barr virus
- how they were originally thought to be contracted
dengue virus (“evil spirit”), influenza virus (the “influence” of bad air)
- combinations of the above
Rous Sarcoma virus
Structure of Viruses
 Viruses consist basically of a core of nucleic acid
surrounded by a protein coat which is antigenic and
specific for each virus type; it protects viral genome
from inactivation by adverse environmental as
nucleases in blood stream.
 Structures which make up a virus particle are:
Virion, Capsid, Capsomeres, Nucleic acid, and
Envelope.
 It varies in size, shape and symmetry
 Virus particles show three types of capsid symmetry:
1. Cubic: in which the particles are icosahedral protein
shells with nucleic acid contained inside, has 20 faces,
each an equilateral triangle. e.g. adenovirus.
2. Helical: Protein binds around DNA/RNA in a
helical fashion (in which the particle is elongated and
in the form of a helix or spiral). Most viruses posses
an outer envelope. e.g. Coronavirus
3. Complex: in which the particle does not confirm
either, e.g. poxvirus .
5 BASIC TYPES OF VIRAL STRUCTURE
icosahedral nucleocapsid
nucleocapsid
lipid bilayer
ICOSAHEDRAL
ENVELOPED ICOSAHEDRAL
helical nucleocapsid
COMPLEX
nucleocapsid
lipid bilayer
glycoprotein spikes
= peplomers
HELICAL
ENVELOPED HELICAL
VIRAL STRUCTURE (virion)
1. Protect genome during
passage from one cell to
another
2. Aid in entry process
3. Package enzymes for early
steps of infection
CAPSID STRUCTURE
1. Helical capsid
 Rod-shaped capsomers
 Coil around hollow
center
 Nucleic acid is kept
inside – wound-up
within tube (Helix )
Morphological types
Morphological types
Helical – capsid surrounds RNA like hollow tube
Ex: Influenza , measles, rabies (enveloped)
Helical symmetry
Morphological types
2. icosahedral
PROTOM
ER
 20-sided with 12 corners
 Vary in the number of
capsomers
 Each capsomer may be made
of 1 or several proteins
 Some are enveloped
Cubic or icosahedral symmetry
ICOSAHEDRAL SYMMETRY
Adenovirus
Enveloped helical virus
Enveloped icosahedral virus
Helical
California Encephalitis Virus
Coronavirus
Hantavirus
Influenza Virus (Flu Virus)
Measles Virus ( Rubeola)
Mumps Virus
Para influenza Virus
Rabies Virus
Respiratory Syncytial Virus(RSV)
Icosahedral
Adeno-associated Virus
(AAV)
Adenovirus
B19
Coxsackievirus - A
Coxsackievirus - B
Cytomegalovirus (CMV)
Eastern Equine
Encephalitis Virus (EEEV)
Echovirus
Epstein-Barr Virus (EBV)
Hepatitis A Virus (HAV)
Hepatitis B Virus (HBV)
Hepatitis C Virus (HCV)
Hepatitis Delta Virus (HDV)
Hepatitis E Virus (HEV)
 Herpes Simplex Virus 1 (HHV1)
Herpes Simplex Virus 2 (HHV2)
Human Immunodeficiency Virus
(HIV)
Human T-lymphotrophic Virus
(HTLV)
Norwalk Virus
Papilloma Virus (HPV)
Polio virus
Rhinovirus
Rubella Virus
Saint Louis Encephalitis Virus
Varicella-Zoster Virus (HHV3)
Western Equine Encephalitis Virus
(WEEV)
Yellow Fever Virus
Complex viruses
 Have additional or special structures
 Examples:
 Poxviruses – lack normal capsid – instead, layers of
lipoprotiens and fibrils on surface
surface view
cross section
A bacteriophage
 A bacteriophage is any one of a number of viruses that
infect bacteria.
 They do this by injecting genetic material, which they
carry enclosed in an outer protein capsid. The genetic
material can be ssRNA, dsRNA, ssDNA, or dsDNA ('ss' or 'ds-' prefix denotes single-strand or double-strand)
along with either circular or linear arrangement.
Phage - viruses have a polyhedral head, helical tail and fibers
for attachment.