doesn’t belong to any kingdom -it’s not a plant or an animal. -it’s not a fungi, protist, or...

VirusesDoesn’t belong to any kingdom

-It’s not a plant or an animal.-It’s not a fungi, protist, or

bacteria.

WHAT IS A VIRUS?

A virus is an infectious agent made up of nucleic acid (DNA or RNA) wrapped in a

protein coat called a capsid.

Viruses have no nucleus, no organelles, no cytoplasm or cell membrane—Non-cellular

vs

This is why it does NOT belong to any kingdom.

DISEASE VIRUSES

AIDS HIV

WartHerpes Simplex Virus

Flu Influenza

Measles Morbillivirus .

Cancer Hepatitis B

Introduction – Structure – Replication – Virology – Medicine - Review

Examples of some viral diseases:

Let’s look at the Defining Properties of Viruses

1. Viruses are parasites that invade cells

2. Viruses have either DNA (Deoxyribose Nucleic Acid) or RNA (Ribonucleic Acid)

3. Viruses direct the synthesis of new virus within a host cell.

4. Newly made viruses infect other cells.


Who do viruses infect?

• Viruses infect Bacteria– These viruses are called bacteriophages

• Viruses infect Plants– One example is the Tobacco Mosaic Virus

• Viruses infect Animals– One example is the flu

Viruses usually infect a specific host including:


Capsid (protein coat)– inside contains either RNA or DNA

1. Bacteriophage—viruses that infect bacteria

Tail fibers– allow attachment to the host

2. Viruses that infect plantsViroids Ex:Tobacco Mosaic Virus

Tobacco Mosaic Virus (TMV) is an example of a virus with a helical structure. Protein subunits wrap around the spiraling RNA strand.


This image taken using an Electron Microscope

Beyond Viruses…… VIROIDS: The Plant Invaders…

A VIROID is a… VIR(virus)OID(like) particle.

Viroids are“sub-viruses” composed exclusively of a single circular strand of nucleic acid (RNA) that codes for a

single protein.

Surface Marker – allows for specific receptor binding

of a host cell

DNA or RNA

Capsid (protein coat)

2. Viruses that infect animals AdenovirusFlu (influenza), pink eye, common cold

Enveloped viruses are viruses which have a membrane coat surrounding the protein coat or capsid.

These viruses are common in animal viruses, but are uncommon in plant viruses.

A PRIONHas protein only, no DNA or RNA (cause of mad cow disease and Creutfeldt-Jacob disease in humans)—Prions (affects the brain and is always fatal)

No DNA or RNA!

Beyond Viruses…Beyond Viroids…

Certain viruses can only attack certain cell types. They are said to be specific.

Surface Markers

Receptor Sites

Example: The rabies virus only attacks brain or nervous cells.

Virus

Cell

Surface Markers

Receptor Sites

Virus

A virus recognizes cells it can infect by matching its surface marker with a receptor site on a cell.

Cell

Replication Phases

V - Release- Assembly of virus

DNA and protein coat into whole new viruses

- Leaving the cell

http://www.cat.cc.md.us/courses/bio141/lecguide/unit2/viruses/adlyt.html

Phase I

Phase II

Phase IV Phase VPhase III


I, II, III - Viruses enter cell- Attachment to cell membrane- Penetration inside cell- Losing virus protein coat

IV - Replication- Tricks cell into making

more viral DNA- Tricks cell into making

viral protein coat

• Two “life” cycles: Lytic & Lysogenic

• Bacteriophages (viruses that attack bacteria) are often studied

• Replication is similar with many animal viruses Dozens of phage viruses attacking an E.

coli bacteria cellThe bacteria cell is destroyed and new viruses escape

1st Step: Attachment– Virus lands on cell

membrane– Virus attaches to a

cell receptor– Virus acts as key;

receptor acts as lock

2nd Step: Entry– Virus enzyme

weakens cell membrane

– DNA/RNA enters the host cell

Another way viruses may enter a cell… through phagocytosis

3rd Step: Replication– Virus DNA/RNA

uses ribosomes to make virus proteins

– Virus proteins created by transcription/ translation

transcription translationViral DNA Viral RNA Viral Proteins

4th Step: Assembly– Virus proteins are

assembled into new viruses

5th Step: Release– Virus enzyme

causes cell membrane to LYSE (burst)

– Viruses are released

– Cycle repeats

LYTIC CYCLE REVIEW

3. 2. 1.

4. 5.

Step 1 Step 2 Step 3

Step 4 Step 5

1st step: Attachment

Same

2nd Step: Entry

Same

cell DNA

Pro-virus

3rd step: Replication –Provirus Created

• Virus DNA combines with cell DNA

– Infected cell divides by mitosis and copies the provirus

–Each new cell will contain the provirus

Virus DNA

Pro-virus

Pro-virus

4th Step: Assembly:new viruses are assembled in many cells

5th Step: Release

many cells burst releasing many more viruses

VIRUSHOST

A living thing that provides a source

of energy for a virus or an organism

PARASITE

Organisms that live on or near a host and cause

it harm.

A tiny, nonliving that invades and then multiplies inside of a cell.

A virus that immediately goes into action. It begins to take over cell functions and produce the virus’s proteins and genetic material.These parts then assemble into new viruses. The viruses multiply like a copy machine left on. When it is full it bursts open – releases the new viruses and dies.

Some viruses hide for a while and become part of the cell’s genetic material. It may stay inactive and “hidden” for years. Then under certain conditions it becomes active and acts like an active virus. Ex – cold sores

Importance: *HarmfulCauses disease—pathogenicDisease producing agent—pathogen

Human Diseases: Warts, common cold, Influenza (flu), Smallpox, Ebola, Herpes, AIDS, Chicken pox, Rabies

Viruses disrupt the body’s normal equilibrium/balanceViruses can be prevented with vaccines, but NOT treated with antibiotics.

Beneficial:Genetic Engineering—harmless virus carries good genes into cells.

(antibiotics treat bacteria)

The End! And Review• Viruses are very simple: a shell containing

either DNA or RNA.They infect by hijacking cells’ machinery to

force them to make more viruses.• Viruses are tiny, even compared to a cell.• Some viruses may prove useful in gene

therapy as natural carriers of DNA that was specially designed to be good for a particular reason.


• RNA virus• Example: HIV• Contain enzyme called

“reverse transcriptase”

• Steps

1) Virus RNA enters host cell

2) Reverse transcriptase changes the virus RNA into DNA

3) Virus DNA combines with cell DNA (provirus created)

4) Cell divides and copies the virus

5) Eventually, the viral DNA becomes active

Retrovirus multiplication

How is HIV contracted?

• High risk activities:– 1) Sex (oral, vaginal, anal)– 2) Sharing needles

(tattoos, piercings, drugs)

• Low risk activities:– 3) Mother to child in womb– 4) Breast milk– 5) Blood transfusions

High Risk Activities

Low Risk Activities

HIV Prevention• 100% Effective:

Abstinence • If sexually active: Latex

condoms are the only forms of birth control that prevent STDs and pregnancy

• If drug user: Change needles

What is AIDS?• Acquired Immunodeficiency Syndrome• More than 1.2 million people in the United States are living with HIV

infection• Almost 1 in 7 (14%) are unaware of their infection.• CDC estimates that 1,201,100 persons aged 13 years and older are

living with HIV infection• The estimated incidence of HIV has remained stable overall in recent

years, at about 50,000 new HIV infections per year.• In 2013, an estimated 47,352 people were diagnosed with HIV

infection in the United States. • In that same year, an estimated 26,688 people were diagnosed with

AIDS. • Overall, an estimated 1,194,039 people in the United States have

been diagnosed with AIDS.

AIDS results when….???“AIDS” refers to the late stage of HIV infection, when an HIV-

infected person’s immune system is severely damaged and has difficulty fighting diseases and certain cancers.

1) Amount of T-cells drop (200 T-cells per 1mm³ blood)

2) Multiple symptoms/infections appear• Rash, fever, headache, sore throat, swollen

lymph nodes• Therefore, the HIV virus causes the disease AIDS

by killing your T-cells

More on AIDSBefore the development of certain medications,

people with HIV could progress to AIDS in just a few years.

But today, most people who are HIV-positive do not progress to AIDS because of antiretroviral therapy (ART)

You can keep the level of HIV in your body low. This will help keep your body strong and healthy and reduce the likelihood that you will ever progress to AIDS. It will also help lower your risk of transmitting HIV to others.

Virus Living CellRNA or DNA core (center),

protein coat (capsid)

Copies itself only inside host cell--REPLICATION

DNA or RNA

NO

NO

NO

NO

Cell membrane, cytoplasm, genetic material, organelles

Asexual or Sexual

DNA and RNA

YES—Multicellular Organisms

YES

YES

YES

Structure

Reproduction

Genetic Material

Growth and Development

Response to Environment

Change over time

Obtain and Use Energy

doesn’t belong to any kingdom -it’s not a plant or an animal. -it’s not a fungi, protist, or...

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