1. Virus Notes
Ch. 18 Sec. 1,2,3

2. IMPORTANT TERMS HOST – 2. RETROVIRUS -
AN ORGANISM THAT SHELTERS AND NOURISHES SOMETHING.
2. RETROVIRUS -
A VIRUS THAT REPLICATES BY FIRST TRANSCRIBING RNA INTO DNA. (HIV)

3. 3. Vaccine 4. VIROID - 5. PRION -
A substance produced from “killed” or weakened pathogens
4. VIROID -
A SINGLE STRAND OF VIRAL RNA. (PLANT DISEASES)
5. PRION -
VIRAL PROTEIN MOLECULE. CAUSES DISEASES IN ANIMALS. (MAD COW DISEASE/Creuzfeldt-Jakob).

4. 6. CAPSID - 7. PROPHAGE/PROVIRUS - 8. LYSIS - BACTERIOPHAGE-
THE PROTEIN COAT OF A VIRUS.
7. PROPHAGE/PROVIRUS -
A VIRAL DNA SEGMENT INSERTED INTO A BACTERIAL CELL
8. LYSIS -
THE BREAKING APART OF THE CELL TO
RELEASE NEW VIRUSES.
BACTERIOPHAGE-
A VIRUS THAT ATTACKS A BACTERIA.
Read Ch. 18, Sec. 1,2,3 pages

5. CHARACTERISTICS OF VIRUSES
VIRUS – (POISON)
DISCOVERED BY STANLEY
– 1935
- TMV (Tobacco Mosaic Virus)
Viruses are pathogens—agents which cause disease

6. Debate on living vs. nonliving
Not normally classified (not in a Domain, Kingdom, etc; no genus species name)
Considered NONLIVING because they
can only reproduce inside of living cells
do not have a metabolism
do not maintain homeostasis
do not grow
Viruses are similar to living cells in that they
Have genetic material (DNA or RNA)
Have proteins
Have receptor/marker molecules on the outside for communication/recognition
Change over time (mutate/evolve)

8. Viral Structure

9. STRUCTURE OF A VIRUS 2 Parts:
CORE OF NUCLEIC ACID --NUCLEIC ACID IS EITHER DNA OR RNA
PROTEIN COAT
--PROTEIN COAT is called the CAPSID

10. FIVE BASIC SHAPES OF VIRUSES
helical
spherical
polyhedral
binal/bacteriophage
filovirus

12. HELICAL RNA or DNA coiled in a long, narrow capsid
Ex) tobacco mosaic virus (TMV)

13. SPHERICAL
Typically studded with receptors, may be enveloped (envelope around capsid)
Ex) Influenza (flu) virus; HIV

14. POLYHEDRAL VIRUS Geometric appearance
Ex) adenovirus (causes the common cold)

15. BINAL Polyhedral capsid containing DNA or RNA Helical tail
Ex) Bacteriophage (ONLY infect bacteria)

16. FILOVIRUS No distinct or uniform shape Threadlike loops
filovirus Filoviridae Photo Album
Ex. Ebola
Deadly viruses; many are emergent viruses – viruses that humans have suddenly contracted in isolated geographic areas
Ex) Hantavirus and West Nile virus are emergent viruses (however they are NOT filo shape)
No distinct or uniform shape
Threadlike loops

17. Surface Marker/Receptor Proteins
Virus surface proteins attach to cell surface proteins much like pieces of a puzzle fit together.
This facilitates their entry across the cell membrane.
influenza
cell

18. Viral Diseases (p. 440) Cold *Influenza (flu)
AIDS Small pox (variola)—vaccine by Jenner
*Measles *Chicken pox (varicella)
*Mumps *Polio—vaccine by Salk
Mononucleosis Ebola
Hepatitis (ABC) Yellow fever
SARS *Rabies
*Rotavirus *Rubella (German measles)
*Routinely immunized against
NO Viral diseases are treatable with ANTIBIOTICS!!!

19. WARTS
- are caused by viruses!

20. Viral Replication Viruses replicate inside living cells
They enter a cell by injecting their genetic material into the cell
tears in the plant cell wall
binds to molecules on the cell surface and triggers endocytosis.

21. RETROVIRUS Viruses that get their genetic material copied backwards…
From RNA to DNA
Ex) HIV (or human immunodeficiency virus) causes disease AIDS
contain RNA & inject it into the host cell
When the virus infects the cell, they produce a DNA copy of their RNA
Responsible for some types of cancer in animals

22. 2 cycles for Viral Reproduction
1. Lytic Cycle
2. Lysogenic Cycle

23. Lytic Cycle
Characterized by viral infection, replication, and cell destruction
Virus enters cell, often just the genetic material is injected.
Replicates viral genes by making new protein coats or capsids by gene expression and new nucleic acids (DNA or RNA) by replication.
Soon the cell is full of new viruses that burst from the cell spreading the disease

25. LYTIC CYCLE VIRUS ATTACHES TO HOST
VIRUS ATTACHES TO HOST
VIRUS ENTERS CELL (NUCLEIC ACID IS INJECTED)
REPLICATES IMMEDIATELY
PRODUCES MANY NEW VIRUSES
VIRUSES BURST FROM CELL TO INVADE OTHER CELLS (This is the step that harms or kills the cell)

26. Lysogenic Cycle
the viral genome replicates without destroying the host cell
virus inserts its DNA into its host DNA and it “hides” there
Becomes a provirus/prophage
Divides/replicates with the “help” of the host cell
ALL WITHOUT HARMING THE CELL
Later it will begin the lytic cycle to spread the virus

28. LYSOGENIC CYCLE VIRUS INVADES CELL DOES NOT IMMEDIATELY KILL HOST CELL
BECOMES PART OF HOST’S DNA
HOST CELL REPRODUCES AS USUAL (MAKING MORE VIRAL DNA WITHOUT KNOWING IT)
EVENTUALLY GOES INTO LYTIC CYCLE TO SPREAD THE VIRUS

29. VIRAL REPLICATION CYCLES

31. HUMAN IMMUNODEFICIENCY VIRUS—a retrovirus
HIV, the virus that can result in the disease AIDS, can hide for years in the nucleus of T-cells (white blood cells that help fight infection) in the Lysogenic cycle. People can have no symptoms, yet be spreading the disease to many partners.

32. HIV then begins the Lytic cycle and T-cells begin to die.
HIV infection leads to the destruction of the body’s T cells and weakens the immune system. This can lead to AIDS (when T cell count is below 200 cells/ml).
The patient eventually dies from another disease (opportunistic infection) that the immune system can’t control because there are not enough T-cells to help fight infection.

33. Structure of HIV Exterior Viral envelope studded with glycoproteins
Lipid bilayer made from host cell membrane
Inside is capsid
Inside 2 molecules of RNA

34. Viruses and Cancer Many cancers can result from viral infections
HOW? Because when a virus infects a cell it can cause genes in the cell to turn on or off. This can interrupt the cell cycle, causing the cell to divide uncontrollably. This is cancer!
Ex) HPV – this virus can infect women and result in cervical cancer; there’s a vaccine on the market now
Ex) hepatitis – can often lead to liver cancer
Ex) Epstein-Barr virus – can lead to some lymphomas

35. Viruses have 2 basic components__________________
Wrap Up
Viruses (as well as viroids and prions) are disease-causing “organisms” that are not considered to be alive according to current cell theory for several reasons __________________
The diseases caused by viruses CANNOT be treated with antibiotics, but many have vaccines given via a vaccination.__
Viruses have 2 basic components__________________
Viruses have 5 basic shapes_________________________
Viruses replicate/reproduce inside host cells; retroviruses have an unusual method of replication RNA to DNA.
Viruses that infect bacteria (bacteriophages) have 2 basic life cycles ___________________
AIDS and cancer, as well as many common infections (colds, influenza), are caused by viruses