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

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. 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).

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 526-538

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

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)

Viral Structure

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

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

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

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

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

BINAL Polyhedral capsid containing DNA or RNA Helical tail Ex) Bacteriophage (ONLY infect bacteria) http://www.cellsalive.com/phage.htm

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

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 http://www.virology.ws/2009/05/04/influenza-virus-attachment-to-cells/

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!!!

WARTS - are caused by viruses!

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.

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

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

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

LYTIC CYCLE VIRUS ATTACHES TO HOST http://biology.about.com/library/blvirusanim.htm 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)

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

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 http://student.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/lysosum.html

VIRAL REPLICATION CYCLES

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.

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.

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

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

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 http://www.npr.org/templates/story/story.php?storyId=114075029&sc=emaf