Download Viral Structure and Reproduction PAP

Are viruses living organisms?
For several reasons, viruses are not
considered living organisms.
• Viruses
– are not made of cells
– cannot reproduce on
their own
– do not grow or divide
– do not use energy
– lack machinery for
protein synthesis
However, viruses infect living things & can
pass from host to host.
Compare these viruses.
How are the structures similar?
How are they different?
All viruses have the same major parts, but
each virus infects a specific type of host.
Why are viruses so specific?
Viral Structure & Reproduction
Viruses have a very simple structure.
• All viruses have:
– Nucleic Acids: DNA or RNA
– Capsid: protein coat that determines the shape &
infection process & houses nucleic acids
Viral Structure
• Some viruses have a lipid envelope, a protective outer
coat.
Influenza
Rabies
What type of nucleic acids do viruses use?
A. DNA
B. RNA
C. Can be DNA or RNA
D. Carries both DNA & RNA
E. Protein
What macromolecule are capsids made of?
A. Carbohydrates
B. Nucleic Acids
C. Lipids
D. Proteins
What is one function of the viral capsid?
A.
B.
C.
D.
Produce toxins
Gives the virus a shape
Synthesize proteins
Communicate with other
viruses
The viral shape is determined by the capsid.
Helical
Polyhedral
Spherical
Bacteriophage
Which type of cells do bacteriophages infect?
A.
B.
C.
D.
Immune Cells
Phage Cells
Viral Cells
Prokaryotic Cells
Bacteriophage
The name tells you that
this virus infects
bacteria!
What are the effects of being infected by this
virus?
A.
B.
C.
D.
You will get AIDS.
You will get the flu.
You will get a cold sore.
You will get the Bubonic
Plague.
This name tells you
that this virus causes
influenza (the flu)!
A cell’s membrane won’t let just any ol’ particle
in, so why do cells allow viruses to infect them?
They have no choice!
• Viruses mimic molecules a
host cell wants & needs to
take in.
• Viruses “trick” the host cell
into letting the virus in.
Viral Attachment
• The specificity of membrane
receptors forces viruses to have
specifically shaped antigens on
their surface.
This is what makes viruses
species-specific!
Which type of cell would be infected by this virus?
THE BRAIN CELL
Compare the proteins on the surface of
the cell & the virus. They match like
puzzle pieces!
A
B
C
D
How do viruses reproduce?
Viruses have to insert their genetic
material into the host cell.
What happens once the virus is inside?
Viral Reproduction
Viral Reproduction
• Once a virus enters a host cell, 1 of 2 processes will
occur:
– Lysogenic Cycle
– Lytic Cycle
The Lytic Cycle
The Lytic Cycle
1.
2.
3.
4.
5.
Viral nucleic acid is injected into the host cell.
Host cell begins to make mRNA from the viral DNA.
Viral proteins shut down the host cell’s regular functions.
Cell is used to make thousands of viruses.
Host cell bursts (lyses) & releases viruses to infect other
cells.
This is a cell lysing with new viruses.
Viruses that cause a host cell to burst
are referred to as virulent viruses.
The Lysogenic Cycle
The Lysogenic Cycle
1.
2.
3.
4.
Viral nucleic acid is injected into the host cell.
DNA is integrated (joined) into the host DNA.
Host cell continues dividing with the virus DNA.
Eventually, the viral DNA can be triggered to enter the lytic
cycle.
Viruses that use this cycle are
called temperate viruses.
Ever had a cold sore?
• Cold sores are caused by a strain of the Herpes virus.
• This virus enters the lysogenic cycle, but can enter the
lytic cycle if your immune system is weakened. This is
when you get a cold sore!
Which cycle will
spread viral DNA to
other cells?
A.
B.
C.
D.
Lytic Cycle
Lysogenic Cycle
Both
Neither
Which cycle stops the host cell’s functions?
A. Lytic Cycle
B. Lysogenic Cycle
C. Both
D. Neither
What is the correct sequence of events of the lytic cycle?
Try to do this without looking at your notes. Use logic!
A.
B.
C.
D.
Injection, Transcription, Translation, Assembly, Lysis
Injection, Assembly, Translation, Transcription, Lysis
Lysis, Assembly, Injection, Transcription, Translation
Assembly, Transcription, Translation, Lysis, Injection
DNA vs. RNA Viruses
• DNA viruses don’t mutate as frequently, because they
utilize the host cell’s DNA polymerase.
Why would that matter?
Remember – DNA polymerase
can proofread & correct
errors during DNA replication.
DNA vs. RNA Viruses
• RNA viruses have high mutation rates, because when
the cell copies RNA for new viruses, the enzyme cannot
fix mutations.
You only need a vaccine for
DNA viruses once. For
example, smallpox or HPV.
You need vaccines for RNA
viruses every year, because
they mutate so quickly. For
example, the flu.
RNA viruses are called retroviruses.
• Some cancers, the flu, & AIDS are caused by retroviruses.
• We know RNA is made from DNA, but not the other way
around. (RNA  DNA ???)
How can an RNA virus take over a host cell’s DNA?
Retroviruses
• Retroviruses also need to
inject reverse transcriptase.
• Reverse transcriptase is an
enzyme that makes a DNA
copy of viral RNA.
– RNA  DNA
– The lytic or lysogenic cycle
can then proceed normally.