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Kingdom: Viruses
Biology 11
G. Burgess
What’s a virus
 Complex molecules made of a
protective protein coat that
either covers a RNA or DNA
 They are not ‘living’ yet are
able to reproduce
 They must interact with a
living cell in order to generate
new viral complexes
Structure of a virus
Protein Coat
Protein attachment sites
RNA segments
•Every fall/winter we are infected with the flu virus.
•As the virus is transferred from one host to another,
the RNA is changed by our own cells.
•The proteins on the outside of the virus allow it to
attach to proteins on our cell membranes. Once
attached, the virus is able to release its RNA into our
cells to take control of ribosomes and make copies of
Classification of Viruses
 Viruses are first classified by their
 Viruses infect all living organisms from
monera to fungi to animalia.
 They are also classified by their
biochemical make up and structure
The Baltimore Classification
 Classifies viruses into seven groups by comparing
their nucleic acid (DNA or RNA), strandedness
(single-stranded or double-stranded), and method
of replication.
 Group I: double-stranded DNA viruses
 Group II: single-stranded DNA viruses
 Group III: double-stranded RNA viruses
 Group IV: positive-sense single-stranded RNA
 Group V: negative-sense single-stranded RNA
 Group VI: reverse transcribing Diploid singlestranded RNA viruses
 Group VII: reverse transcribing Circular doublestranded DNA viruses
DNA viruses
 Group 1
 Double
stranded DNA
 ie.
(small pox)
 Group 2
 Single strand
 ie.
Human Papilloma virus
Gynecological tests check for signs of this
cervical cancer causing virus.
RNA viruses
 Group 3
 Double strand
 Ie. Rotaviruses
 Group 4
 Positive-sense
single RNA
 ie. SARS virus,
rubella virus,
polio, HIV
 Group 5
 Negativesense single
RNA strand
 ie. Measles,
mumps, rabis
Small pox, Variola virus
Life Cycle of a virus
 2 parts; lytic and lysogenic cycle
 Lytic cycle:
 Virus identifies and infects a host cell
 Virus takes control of cell’s organelles
(namely the ribosomes) and self
replicates using the materials within
the cell.
 Once new viruses are generated, the
virus causes the host cell to
lysis(break open) and release the
newly created viruses.
Functioning Cycle of a virus
 Lysogenic Cycle:
 Viral DNA may infect the host cell’s
DNA. This is called a provirus.
 Proviruses do not allow other viruses
to infect the cell
 They may carry on normal everyday
activities of the cell or cause changes
in the cell or organism over time.
 These viruses are stimulated by
environmental factors causing the
production of new viruses and the lysis
of the host cell.
 Pp. 338 #1-8
Text: Biology 11, Nelson, 2002.
Biology Living Systems, Glencoe, 1994.
Virus Types,, S.Abedon, accessed Nov.8,
ManBir Online,, accessed
ICTVdB,, Dr.C.Büchen-Osmond,
accessed Nov.8, 2006.