Chapter 13 viruses

Structure of viruses Acellular Either have DNA or RNA Surrounded by a protein coat (capsid). Envelope – proteins, carbohydrates, lipids. Obligate intracellular parasites

complex Complex virus

Lytic cycle

Lambda phage Lysogenized cell Daughter cells descendants Biosynthesis maturation

Animal viruses Papillomavirus (DNA virus) Warts Common warts – legs, hands Direct contact Treated with interferon. Genital warts Finger-like projections (cauliflower) STD, cervical cancer

uncoating

RNA virus, poliovirus Fecal – oral route – contaminated food, water Multiplies in the throat and small intestine CNS – multiplies in the nerve cells, paralysis Polio vaccine

RNA dependent RNA polymerase RNA as a template To make complementary strand of RNA

Retrovirus RNA – genetic material Reverse transcriptase RNA as a template to make DNA Capsid and envelope Human immunodeficiency virus (HIV)

budding

Latent viral infection Herpes simplex virus Dormant – nerve cells, activated under certain conditions – epithelial cells – cold sores Herpes simplex virus 1 – oral herpes Infancy - direct contact Activated by fever, sunburn, stress

Herpes Simplex Virus 2 Genital herpes Vesicles in the area Burning, difficulty walking acyclovir

Viruses and cancer Nucleated cells have proto-oncogenes Control (regulate) cell growth Code for proteins – regulate cell growth Mutation – abnormal proteins Loss of control – uncontrolled proliferation of the cell with mutation - cancer

Mutations Chemicals UV light Viruses Epstein-Barr virus – DNA virus Dormant in some B lymphocytes Transmitted in saliva – infectious mononucleosis

Epstein-Barr virus DNA virus Dormant in some B-lymphocytes Transmitted in saliva Infectious mononucleosis

Burkitt’s Lymphoma Common childhood cancer in Africa Average age 7 – malaria is common EBV and Plasmodium cause mutation in c-myc gene – proto-oncogene Loss of control of cell growth Uncontrolled proliferation Leads to cancer – jaw bones

Human T cell leukemia virus T cell leukemia – retrovirus Average age 45 Transmitted by sexual contact Mutation increases the production of the T cell growth factor. Proliferation of T cells Japan, Caribbean – multistep process

Prions Proteinaceous infectious particles – proteins Scrapie – sheep Scrape themselves against fences Become paralyzed and die Mad cow disease – bovine spongiform encephalopathy (BSE) – sponge like degeneration of the brain. Shake, shiver

Creutzfeldt –jakob disease Occurs in certain families – hereditary Transmitted by contaminated hamburgers Dementia – die within a year

viroids Naked piece of RNA Plant pathogen Potato spindle tuber viroid Damage to potato plants Evolved from introns