Viruses What are the characteristics of living organisms? Living things… are made of cells grow and develop reproduce respond to their environment adapt to their environment obtain and use energy produce wastes 1

Magnified image of a virus Viruses Magnified image of a virus Image of an animal cell viruses on their own can be considered lifeless chemicals, unless ……? 2 2

Viruses Answer viruses are not considered to be living organisms because: 3 3

Typical Viral Stucture 4 4

Viral Capsids Examples:

Viral Classification Viruses are generally classified by: 1. host range (types of cells that the virus can infect) examples: a) cold virus b) rabies c) HIV d) bacteriophage 2. size and shape of the capsid type genetic material (human respiratory cells) (nerve cells in dogs, rodents, humans) 6

Viral Size very small, measured in units called nanometres (nm) 1nm = 1X10-9 m (billionth of a metre) size ranges from 20 - 400 nm 7

Viral Replication Process by which the virus and its genetic material are duplicated before its host cell divides 4 Basic Steps Virus chemically recognizes a , attaches to it, and enters it (either the whole virus or only its genetic material – for some viruses, this can be DNA or RNA). Newly incorporated viral DNA or RNA directs the host cell to (nucleic acids, enzymes, capsid proteins, and other viral proteins)

These viral components are brought together and assembled into The newly formed virus particles are released from the . This is called . Steps 1 through 4 = and may be completed in as little as 25-45 minutes and produces hundreds of new virus particles.

Lysogenic Cycle Some viruses (e.g., that infect bacteria or cause cancer) may coexist with a cell and be carried through The virus’ genetic material is integrated into that of the host cell, however instead of , this newly replicated genetic material is . The virus in this case is in a dormant state called and may be activated by stimuli such as . Once activated, the viruses trigger the .

Viruses & Human Health‏ June 23, 2009

cause cells to become cancerous Viral diseases are difficult to treat because: ex. a) Herpes Simplex Virus I (HSV I) (cold sores) b) HIV Some viruses are cause cells to become cancerous onco = tumour (AIDS) (genital warts) (cervical cancer) ex. Human Papiloma Virus (HPV) April 14, 2019 SBI3C 13

Protection Against Viral Diseases  vaccines: people are given a dead or weakened form of the virus builds up an army of WBC’s & antibodies to kill the living virus immediately before it can reproduce ex. polio vaccine, hepatitis B vaccine Antibiotics antiviral agents: ex. Valtrex – helps heal and decrease pain (herpes) SBI3C

Viral Uses In Medicine 1. Viral Vectors Viruses can be used for gene therapy as “carriers” Viral core is removed & desired human gene is added Virus is mixed with living cells Virus attaches to human host cell & injects the human gene i.e. acts like a microscopic hypodermic needle (Dr. John Bell) OHRI (Ottawa Health Research Institute): University of Ottawa professor success with mice injected cancer cells : also trials in humans that didn’t respond to conventional cancer treatments (chemotherapy & radiation) tumours receded wthin weeks cancer cells give off hormones that inhibit immune response also found that viruses stimulated response & person was immune to that form of cancer for life 15

SOME EXTRA INFO ON HIV…

Worldwide HIV Distribution Note: Total exceeds 100 percent due to rounding. Source: UNAIDS, 2006 Report on the Global AIDS Epidemic, 2006.

Structure of HIV