Transcript Plate 31 - Introduction to Viruses

Plate 31
Introduction to Viruses
Diseases Caused by Viruses
•
Smallpox
•
Chickenpox
•
Influenza (“the flu”)
•
Herpes
•
Polio
•
Rabies
•
Ebola
•
Human Papillomavirus (HPV)
•
Human Immunodeficiency Virus
Virus Size
Viruses can only seen
by electron
microscopes
Average size is
measured in
nanometers (nm)
Bacteria & human cells
are measured in
micrometers (1000
times larger than nm)
Size Comparison
E. coli is 3000 nm in size
Chlamydia trachomatis is
300 nm in size
Rabies virus is 200 nm in
size
Two General Shapes
•
Viruses can come in a wide variety of shapes, but
generally they are either helical or icosahedral
Helix
Icosahedron
Viral Components
Nucleic Acid – either
DNA or RNA that
controls viral
replication
Capsid – outer protein
coat for protection
(made of capsomeres)
Lipid envelope –
flexible outer
membrane, from host
cell
Viral Genetic Material
DNA
RNA (retroviruses)
Lipoprotein Coat
Cell membrane from
killed host cells
Can protect against
host immune system
“Cloak of invisibility”
Obligate Intracellular Parasites
Viruses are sometimes referred to as “obligate
intracellular parasites”
Obligate – needed / necessary
Intra – within
Cellular – relating to cells
Parasite – one organism harms another in a
long-term interaction