For unlimited access to Class Notes, a Class+ subscription is required.
Chapter 35 – Viruses
Viruses are obligate intracellular parasites – HOST CELL does everything!
They have no metabolism, cannot replicate on their OWN, (no amino acids, proteins, nucleic
acids), no plasma membrane, HAVE a genome (DNA/RNA – can be single stranded or double)
When outside host cell – simply not active (dead)
VERY abundant (10X # of prokaryotes) , diverse and cause diseases – illness and death in
STURCTURE OF VIRUS
1. Protein SHELL (capsid) > has HEAD and TAIL
2. Head: made of protein coat, contains genetic material (DNA/RNA)
3. Capsid: Protein Coat (envelope in viruses)
4. Tail: used to ATTACH and put genetic material into the host
To Study Viruses:
Nano biology: virus-infected cells are taken from the hosts and grown in a growth culture, and
the virus is isolated, the virus is exposed to clean cells.
Virus Morphology: shaped like rods, polyhedrons, spheres, and complex heads/tails
NON-enveloped with Capsid Shell
Enveloped with capsid shell plus an additional HOST derived layer
Virus Growth: NEED host cell to DO everything!
Lytic cycle: virus attaches to host cell, genetic material is injected into the cell (viral genomeis
transcribed/ viral proteins are produced), Viral genome is replicated (LYSOGENIC CYCLE), The
new viruses assemble inside the host cell, Viruses are released and the HOST CELL DIES.
(LYSIS) , they are now transmitted to a new host.
Lysogenic cycle: virion enters cell, DNA attaches to host’s DNA, DNA replicates, cell divides
and is passed onto daughter cells
Latent: virion enters cell, viral genome resides in cell (dormant) RESSEMBLES later on, may or
may not integrate with host chromosome.
Antiviral drugs target REPLICATIVE (lytic) phase
LATENT infection is not treatable by antivirals
6 PHASES OF VIRAL REPLICATION
1. Attachment and Entry