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”