Viruses & other Pathogens

The 8 characteristics of Living things Everything is made of cells Reproduction Metabolism Homeostasis Heredity Responsiveness Growth & Development Change over time/adapt

A virus is a tiny, nonliving particle that enters and then reproduces inside a living cell. No organisms are safe from viruses.

Most biologists today consider viruses to be nonliving because viruses do not have all the characteristics essential for life. Viruses are not cells and do not use their own energy to grow or to respond to their surroundings. Viruses also cannot make food, take in food, or produce wastes.

Almost all viruses destroy the cells in which they multiply.

All viruses have two basic parts: a protein coat that protects the virus and an inner core made of genetic material.

The Structure of a Virus Protein Capsule Surrounds genetic material DNA RNA No means of independent metabolism or growth No means of independent reproduction Dependent on host life form Can evolve or change over time http://library.thinkquest.org/C0123260/basic%20knowledge/DNA.htm http://www.laportecounty.org/departments/animal_shelter/rabie_virus.html

The three ways of Entry into Host Cell Plants – through tear in cell wall of cell Bacteria – punches hole and injects DNA or RNA bacteriophage Animals – Endocytosis – cell engulfs bacteria http://www.britannica.com/EBchecked/topic-art/101396/698/Adsorption-to-and-entry-into-a-cell-of-an-enveloped http://bio-microscope.blogspot.com/2008/03/article-virus-structure-and-system.html

Virus as Pathogen – disease causing agent Mumps http://www.southlakeland.gov.uk/Default.aspx?page=1466 Measles Chicken Pox http://www.ndsc.ie/hpsc/A-Z/VaccinePreventable/Measles/Factsheet/ http://www.vaccineinformation.org/photos/variaap005.jpg AIDS Rabies Cold Hanta Hepatitis Flu Polio SARS Hemorrhagic Fever Yellow Fever Small Pox http://www.indiana.edu/~pirt/bioterrorism/diseases-smallpox.html

Mode of Transmission Insects – ticks, mosquitoes Exchange of body fluids – sex, kissing, even oral sex, sometimes sweat Airborne – coughing, sneezing puts viral particles out in aerosols Direct contact – touching; many viruses such as flu and cold are long lived on surfaces

Host Cell Specificity http://www.cdc.gov/ncidod/diseases/hanta/hps/noframes/phys/printtechsection.htm Many can only infect certain tissues or types of cells (must have proper receptors) Hepatitis – liver cells Many cancers – human papilloma virus – Influenza, Hanta virus – lung tissue Tobacco Mosaic Virus – only plant cells

Combating Viral Pathogens Vaccines – A substitute host such as fertilized chicken egg is infected Eggs produce antibodies to combat virus Virus is heat killed & antibodies are injected in a vaccination Jenner – cowpox injected to combat small pox Class of drugs called interferons work by hindering the uptake of viral particles in cells – commercial - Tamaflu

Uses for Viruses Non – pathogenic viruses Pathogenic viruses Used in genetic engineering to transfer genetic material Pathogenic viruses Biological Warfare Smallpox Ebola and other hemorrhagic fevers http://incontiguousbrick.wordpress.com/2007/05/17/911-truth-virus/

Prions – mad cow disease - bse Bovine spongiform encephalopathy Incorrectly folded proteins Cause normal proteins to fold in such a way as to be not functional http://biomed.brown.edu/Courses/BI108/2006-108websites/group09artificialblood/index.htm http://www.biophys.uni-duesseldorf.de/research/prions/index.html http://www.bioquest.org/bedrock/problem_spaces/prion/background.php

Do viruses have the characteristics of living things? Cellular organization NO Reproduction with help from host cells Metabolism NO Homeostasis NO Heredity with help from host cells Responsiveness limited Growth & Development NO