VirusesVirusesIntroductionIntroduction
A virus is a tiny A virus is a tiny nonliving particlenonliving particle that enters and then that enters and then reproduces inside a living cell. reproduces inside a living cell.
Some of the organisms Viruses infect include: 1. Some of the organisms Viruses infect include: 1. HumansHumans
2. Plants2. Plants
3. Animals3. Animals
4. Bacteria4. Bacteria What do you call aWhat do you call a VVirusirus that infects bacteria?that infects bacteria?
BacteriophageBacteriophage which meanswhich means ““bacteria eaterbacteria eater””
VirusesVirusesIntroductionIntroduction
What is an InfectionWhat is an Infection? ?
When bacteria or viruses cause a When bacteria or viruses cause a disease or an illnessdisease or an illness
The virus is called aThe virus is called a parasiteparasite.. Parasite Parasite can only live in acan only live in a hosthost
What is aWhat is a host?host?
An organism that provides energy and a An organism that provides energy and a suitable environment/home for asuitable environment/home for a parasiteparasite
How big are they?How big are they? What size is the What size is the
bacterium bacterium ??
750nm750nm
What size is the What size is the Red Blood Cell?Red Blood Cell?
7,500nm7,500nm
What size is the What size is the influenzainfluenza virus?virus?
90nm90nm
The Structure of The Structure of VirusesViruses
All viruses have two basic partsAll viruses have two basic parts
1. 1. A protein coat A protein coat that protects that protects the virus called the virus called CapsidCapsid
2. An inner core 2. An inner core
made of made of
genetic genetic
material material DNADNA
or or RNARNA
Some viruses Some viruses
are surrounded are surrounded
by an by an
Membrane Membrane
envelope.envelope.
DNA and RNA virusesDNA and RNA viruses T4 bacteriophage T4 bacteriophage
is a is a DNADNA virusvirus
Magnification:Magnification:
x55,065x55,065
Some viruses have Some viruses have RNARNA instead of instead of DNADNA
HIVHIV is type of is type of RNARNA virusvirus
How do viruses How do viruses attach to a Host attach to a Host
cell?cell?
Viruses have outer Viruses have outer
membrane proteinsmembrane proteins
The host cell The host cell
membrane also has membrane also has
proteins on itproteins on it
The The hosthost and the and the
virus virus
surface proteinssurface proteins fit fit
together like a together like a
“ “LOCK AND KEYLOCK AND KEY””
If these do not fit If these do not fit
together the virus together the virus
will not be able to will not be able to
attach to the host attach to the host
cell and cell and infect it infect it !!
BacteriophagBacteriophagee
Virus that infects only Virus that infects only bacteriabacteria
The The DNADNA is inside the headis inside the head
The head is made of special The head is made of special protein coat called:protein coat called:CAPSIDCAPSID
The tail contracts and The tail contracts and pushes the pushes the DNADNA inside the inside the bacteriabacteria
The fibers have special The fibers have special Binding proteinsBinding proteins that that attach to bacterial cell wallattach to bacterial cell wall
BacteriophagBacteriophagee
The head passes its DNA The head passes its DNA
down the tail and into down the tail and into
the host (bacteria)the host (bacteria)
Within Within 25 minutes25 minutes the the
dying bacteria is dying bacteria is
teeming with about 100 teeming with about 100
fresh copies of the virusfresh copies of the virus
Viruses use the Viruses use the
bacteria’s machinery bacteria’s machinery
such as the such as the Ribosomes Ribosomes
to make proteins needed to make proteins needed
to assemble new virusesto assemble new viruses
How Active Viruses MultiplyHow Active Viruses MultiplyACTIVE VIRUSESACTIVE VIRUSES enter cells and immediately begin to enter cells and immediately begin to
multiply, which may lead to the quick death of the invaded multiply, which may lead to the quick death of the invaded
cells.cells.
Active viruses causeActive viruses cause ACUTE INFECTIONACUTE INFECTION which only last which only last
few daysfew days
How Active Viruses Multiply
Virus attaches to the surface of a living cell.
Virus injects genetic material into cell.
Cell produces viral proteins and genetic material.
Viruses assemble.
Cell bursts, releasing viruses.
How Hidden Viruses MultiplyHow Hidden Viruses Multiply HIDDEN VIRUSES “hide” inside host cell before becoming active. Hidden viruses cause CHRONIC
INFECTION which can last a lifetime
How Hidden Viruses Multiply
Virus attaches to cell.
Virus injects its genetic material.
Virus’s genetic material becomes part of cell’s genetic material.
Cell produces viral proteins and genetic material.
Viruses are assembled
Cell bursts, releasing viruses.
Review QuestionsReview Questions
Question: What Question: What kind of organismskind of organisms do viruses infect? do viruses infect?
Answer: Humans Animals Bacteria PlantsAnswer: Humans Animals Bacteria Plants
Question: Explain the difference between a Question: Explain the difference between a hosthost and a and a parasiteparasite
Answer: * Answer: * HostHost is the infected organism, provides suitable is the infected organism, provides suitable homehome
for the parasitefor the parasite
* * ParasiteParasite needs a host to live needs a host to live
Question: What is the name of a virus that infects Question: What is the name of a virus that infects only only BacteriaBacteria??
Answer: A Bacteriophage or T4 phageAnswer: A Bacteriophage or T4 phage
Question: Name the Question: Name the basic partsbasic parts of a virus of a virus
Answer: * Protein coat called “Answer: * Protein coat called “CapsidCapsid””
* * DNADNA or or RNARNA
* Some viruses have an “* Some viruses have an “outer membraneouter membrane””
Question: What type of Question: What type of genetic materialgenetic material is inside a virus? is inside a virus?
Answer: Either Answer: Either DNADNA oror RNARNA but not both but not both
Question: Briefly describe what is an “Question: Briefly describe what is an “Active VirusActive Virus” ?” ?
Answer: * Active virus infects a host and multiplies Answer: * Active virus infects a host and multiplies immediately immediately
* Causes “* Causes “Acute InfectionAcute Infection” ”
* Example: the Flu* Example: the Flu
Question: Briefly describe what is a “Question: Briefly describe what is a “Hidden VirusHidden Virus”?”?
Answer: * Infects a host but doesn’t multiply Answer: * Infects a host but doesn’t multiply immediatelyimmediately
* Causes “* Causes “Chronic InfectionChronic Infection” ”
* May last a lifetime* May last a lifetime
* Example: The HIV that causes AIDS * Example: The HIV that causes AIDS
Herpes Epstein-BarrHerpes Epstein-Barr
Question: How do viruses attach to a host cell?Question: How do viruses attach to a host cell?
Answer: Both the host and virus have special proteins Answer: Both the host and virus have special proteins that fitthat fit
together like a together like a ““Lock and Key”Lock and Key”