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Warm-Up
What makes something alive?
Is the common cold a virus or a bacteria?
When is your project (Data Table and Graphs) due?
How the flu invades your
body!
Video
Video
I. What is a virus?
- a virus is a tiny particle made of
information
electron micrograph
of a cluster of
influenza viruses
protein and genetic
Basic Virus Structure
Genetic
material
Head/
Capsid
Tail fibers
A virus has 2 parts
1) genetic material a) the genetic information in viruses may be either RNA or DNA.
2) Capsid
Capsid
a) the Capsid is a shield
made of protein that
protects the genetic
material.
Bacteriophage –
a virus that
attacks bacteria
II. What Do Viruses Do?
- viruses inject other cells with their genetic material in order to
reproduce
-each type of virus infects a particular kind of
organism
cell in a specific
-the specific organism that a virus attacks is called its host
III. How Do
reproduce?
REPLICATION
Viruses
Steps of Lytic Viral
Replication
1. The virus attaches to a
host cell
2. The virus injects its
information into the host cell
3. The genetic information of
the virus takes control of the
host cell and orders the
production of new viruses
4. New viruses are assembled in the host cell
5. So many viruses are made inside the host
cell that the cell bursts (lysis)
6. The new viruses leave the host cell and go
on to infect new cells.
LYSOGENIC Replication is a little different…
The first two steps are the same.
After the virus injects its information into the host
cell, the viral DNA becomes part of the host DNA.
Every time the host cell goes through cell division,
the viral DNA is replicated and is inside each new
daughter cell.
Eventually, the virus goes back into the lytic cycle
step – hijacking the host’s machinery and making
more viruses but now the virus is in a ton of host
cells!
HIV vs Flu
Influenza reproduces through the lytic cycle
HIV reproduces through the lysogenic cycle
Virus vs Cell
Venn Diagram
Similarities: genetic material, protective coating, can reproduce.
Differences: cell reproduces without a host, virus only reproduces with
a host, cell has organelles/nucleus/cell membrane, virus has a capsid,
cell is alive, virus is not
Review
Virus Video
Mythbusters
It's easy to mix these up since compared to us, both are
VERY SMALL.
But...
Bacteria, given the proper nutrients, can grow and
reproduce on their own
Viruses cannot "live" or reproduce without getting inside
some living cell, whether it's a plant, animal, or bacteria.
compared to viruses,
bacteria are HUGE
◦ Antibiotics are often
used to fight off bacterial
infections
◦ Since a virus is not a
living cell, antibiotics
used to fight living
bacteria will not be
effective on viral
illnesses
Should you still take an antibiotic “just in case” or
to help relieve your symptoms?
◦ NO!!!
◦ This will only lead
to antibiotic
resistance of your
immune system,
causing you to get
sicker in the future
Check-Point Questions
Write these in your notebooks.
1. What do viruses depend on for their reproduction?
2. Describe each of the two reproductive paths viruses may follow once
they have entered a cell.
3. What’s the difference between bacterial and viruses?
4. What do antibiotics kill?
Quick review
1. What do viruses depend on for their reproduction? Viruses depend on living cells for
reproduction.
2. Describe each of the two reproductive paths viruses may follow once they have entered
a cell. In a lytic infection, viral genes are quickly transcribed and new viruses are made by
the host cell. In a lysogenic infection, the host cell is not immediately taken over; viral
nucleic acid is inserted into the host cell’s DNA and may be inactive for a long time.
3. What’s the difference between bacterial and viruses?
Bacteria are one-celled organisms; viruses must be inside a cell to live
4. What do antibiotics? Bacteria