Microbiology Online Notes
Overview of Animal Viruses
I. Viruses
A. Obligate intracellular parasites of bacteria, protozoa, fungi, algae, plants, and animals
B. Very small; not visible with light microscope
1. Influenza virus = 100nm or .1um
2. Streptococcus = 1000nm or 1um
3. E. coli = 2um long
4. Yeast and RBC = 7-8um
5. Macrophage = 21um
C. Not a cell
D. Structure
1. Nucleic acid (DNA or RNA, single-stranded or double-stranded)
2. Capsid – protein coat that surrounds nucleic acid
3. Envelope – additional external covering around capsid
4. Naked viruses only contain capsid
E. Avian Influenza Virus, H5N1
1. Envelope around Capsid and Nucleic Acid
2. Hemagglutinin spike (H), Neuraminidase spike (N)
a. Used to ID certain viruses (ex. H5N1)
F. Needs another cell to replicate; only active inside another cell
1. Takes control of the host cell
2. Directs host cells to make copies of new viruses
G. Usually very specific; can only infect specific cells of specific hosts
1. Outer surface of virus must bind to specific receptors on host cell
II. Multiplication of Animal Viruses
A. Attachment (a.k.a. adsorption)
1. Virus attaches to plasma membrane (proteins and glycoproteins)
2. Specific spikes on virus surface must bind to specific receptors on your cells
B. Penetration (a.k.a. Entry)
1. Mechanism of how virus is taken into cell
a. Receptor-mediated endocytosis
b. Fusion of viral envelope with cell membrane
C. Uncoating
1. Viral nucleic acid is separated from its protein coat inside the cell
D. Viral DNA and Viral proteins are made
1. Viral DNA (once uncoated) enters nucleus of cell
2. Viral genes necessary to replicated the viral DNA are transcribed and translated
3. Viral DNA is replicated
4. Viral genes coding for the capsid are then transcribed and translated
5. New complete viruses are assembled in nucleus of host cell
6. New viruses are then released from host cell to infect other cells. The release often
kills the host cell. Also, often the virus itself does permanent damage to the cell.
Can even damage DNA and cause cancer (oncovirus such as hpv).
