Created By: Easter Chang, Adrienne Furneis,
Maggie Hoang and Feeza Mohamad
They are single stranded RNA viruses into
three classes: IV, V and VI according to how
the RNA genome functions in a host cell
Another important characteristic of a virus is
that most of them have a membranous
envelope from the host cell membrane
Classes of Animal Viruses are foung on page
340 (Table 18.1)
-The favored theory of how viruses came to be,
says that they came from bits of nucleic acids
that could move from cell to cell.
-Interestingly enough, viral genomes resemble
its host far more than other viruses, some being
nearly identical.
-Although, most viruses seem to be distantly
related to one another, which is likely due to the
fact that viral genes were successful during their
early evolution, making copious copies of
themselves and "taking over", in a way.
Animal virus that has an outer membrane
used to enter host cells
Does NOT kill host cell
1. Glycoproteins on viral
envelope bind to specific
receptor molecules on
host cell
2. Capsid enters cell &
releases a viral genome
3. Viral Genome acts a
template
4. Complementary strands
made
5. Vesicles transport
envelope glycoproteins
to plasma membrane
6. A capsid forms around
viral genome
7. New Virus buds from cell
free to infect other cells
Viral Glycoproteins
Where?
Protrude from outer surface of envelope
What?
Bind to specific receptor molecule on surface of host cell
Made by?
cellular enzymes in the ER
Some virus’ envelopes are not from the
plasma membrane
Herpesviruses
Envelopes taken from nuclear membrane of host
Double stranded
Reproduce in nucleus
Effects cold sores/genital sores
Most variety of RNA genomes among animal-
infecting viruses
Retrovirus (class VI): animal-infecting, RNA
virus with most complicated reproductive cycle
◦ Reverse transcriptase: transcribes an RNA template to
DNA; goes from RNA DNA
Usually information flows from DNA RNA, and
because these viruses transcribe from RNA DNA
there is “retro” in their name, which means
“backward”
◦ Example: HIV (human immunodeficiency virus) which
causes AIDS (acquired immunodeficiency syndrome)
◦ Made up of two identical RNA strands and two
molecules of reverse transcriptase, safe and sound
because surrounded by viral envelope
How does the retrovirus infect? Let’s use HIV as
an example:
◦ HIV enters the host cell reverse transcriptase help
to transcribe viral DNA
◦ Viral DNA enters the nucleus becomes a part of the
DNA of a chromosome
Provirus: the viral DNA that is integrated into the
chromosome
Provirus does not leave the cell – it is there to STAY!
Provirus transcribes into RNA molecules by
RNA polymerase can function as mRNA that
can create viral proteins as well as a genome