doesn’t belong to any kingdom -it’s not a plant or an animal. -it’s not a fungi, protist, or...
TRANSCRIPT
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.
Introduction – Structure – Replication – Virology – Medicine - Review
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:
Introduction – Structure – Replication – Virology – Medicine - Review
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.
Introduction – Structure – Replication – Virology – Medicine - Review
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
Introduction – Structure – Replication – Virology – Medicine - Review
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
5th Step: Release– Virus enzyme
causes cell membrane to LYSE (burst)
– Viruses are released
– Cycle repeats
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.
Introduction – Structure – Replication – Virology – Medicine - Review
• 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
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