Viruses
Something you don’t want to
catch…
Viruses
1. How do scientists classify things as living?
1. Made of cells
2. Has a metabolism to grow and
reproduce
3. Information stored in DNA
2. Are viruses alive?
NO!
Living or Nonliving?
NONLIVING
LIVING
Viruses
3. What do viruses and
living organisms have in
common?
• Both use nucleic acids to
store genetic information
in the form of DNA or RNA
• Both change over time
(evolve)
Viruses
4. If viruses do not have
their own metabolism
to grow and
reproduce, how do
they survive?
• By hijacking living cells
and using their
metabolism to grow
and reproduce.
There are 2 types of viral infections
• Lytic infection- a virus
enters a cell, makes copies
of itself, and causes cell to
burst .
• Lysogenic infection- a virus
integrates its DNA into the
DNA of the host cell, and
the viral genetic
information replicates
along with the host cell’s
DNA.
Viral Reproduction –
Lytic Cycle
• Lytic Cycle
• Attaches to host (1)
• Injects genetic material into host(2)
• Cellular machinery duplicates genetic material and creates viral
proteins (capsids, tail fibers) (3)
• New viruses are assembled (4)
• New viruses exit the cell by bursting the cellular membrane (5)
• End result – more viruses made, cell dies
Viral Reproduction –
Lytic Cycle
Attachment
Lytic Cycle
Entry
Release
Assembly
Replication
Viral Reproduction –
Lysogenic Cycle
• Lysogenic Cycle
•
•
•
•
•
Attaches to host
Injects genetic material into host
Viral genetic material is inserted into host genome (6)
Viral genetic material lies dormant (6)
When cell reproduces, new copies have viral genetic information
(7)
• When virus is ready to exit dormant stage it will separate from
cell’s DNA and enter Lytic cycle (8)
• End result – more viral genome made, cell lives
Viral Reproduction –
Lysogenic Cycle
Lysogenic Cycle
Attachment
Entry
Separation
Insertion
Reproduction
Viral Reproduction
Lytic Cycle
•New viruses made
•Cellular host dies
Lysogenic Cycle
•Genome copies made
•Cellular host lives
Viruses can use both cycles
1.Infect many cells with lysogenic
2.Create many viruses at once with lytic
Viral Reproduction
Lytic & Lysogenic Cycles
Virus Types
• Bacteriophages = are
viruses that attack
bacteria
• Retroviruses = viruses
that use RNA to
reverse transcribe DNA
that integrates into the
host genome.
Example: HIV
More Virus Types
• What makes these viruses different
from bacteria?
THEY ARE NOT LIVING !
CHECK POINT
• This graphic
shows a virus’
_____ _______.
A. Viral
Reproduction
B. Viral
Transription
How do you treat a virus?
• Remember you cannot treat a viral
infection but you can prevent one by
getting a vaccine.
Vaccine
A vaccine
improves
immunity to
a particular
disease.
How do vaccines work?
• A vaccine contains a weakened strain of
the microbe.
•When injected into your body it stimulates
your immune system to recognize it as
foreign, destroy it, and remember it.
• So if your body encounters the full strain
later, it can easily recognize and destroy it!!!!!
http://health.howstuffworks.com/adam-200097.htm
SUMMARY
Important facts about viruses
• Viruses must be
produced within living
cells
• Viruses destroy the
living cells they grow in
• Viruses gain entry by
specific receptors on
the host cell
Viruses
•How do you catch many
viruses? Through body fluids.
•What are your chances of
catching a virus from
someone in this classroom?
Viral Diseases - AIDS
• AIDS – acquired immune deficiency syndrome
• Describes loss of immune system because of HIV
• Caused by HIV - human immunodeficiency virus
• makes helper T cells useless
• Prevention
• No vaccine
• Limit transmission (use condoms)
• Avoid transmission (use clean needles)
Viral Diseases – AIDS –
HIV Replication
Viral Diseases - AIDS
• Initial infection
• Helper T cells rapidly decline
• Viral genome rapidly increases
• Clinical latency
• Viral genomes lay mostly dormant in infected cells
• AIDS
• Rate of viral creation outweighs helper T cell creation
• Death
• Immune system too weak to fight common pathogens
Viral Diseases - Influenza
• Influenza (the flu)
• Causes fever, fatigue, and respiratory infections
• More severe than common cold, can be deadly
• Caused by a variety of influenza viruses
– Change often, new vaccines yearly
– Can blend with bird and swine
strains to produce new viruses
• Prevention
– Seasonal vaccine
– Limit transmission (wash hands)
Image by NIAD [Public Domain]
Viral Diseases – Common Cold
• The Common Cold
• Causes fever, fatigue, and respiratory infections
• Less severe than influenza
• Caused by a variety rhinoviruses
• Over 200 different virus strains
• Prevention
• No vaccine
• Limit transmission
(wash hands)
Image by Robin S [GNU]
Viral Diseases – Hepatitis A
• Hepatitis A
• Causes inflammation of liver, jaundice appearance
• Rarely results in liver failure
• Caused by a hepatitis A virus
• Carried through infected food or water
• Prevention
• Vaccine
• Limit transmission
(wash hands, food)
Image by The CDC [Public Domain]