Chapter 27

  • View

  • Download

Embed Size (px)


Chapter 27. Viral Genetics. Hepatitis. Viral diseases. Polio. Measles. Chicken pox. Influenza: 1918 epidemic. 30-40 million deaths world-wide. RNA virus. Smallpox. Eradicated in 1976 vaccinations ceased in 1980 at risk population?. Ebola. SARS. hantavirus. Emerging viruses. - PowerPoint PPT Presentation

Text of Chapter 27

Chapter 18.SARS
AP Biology
DNA or RNA enclosed in a protein coat
Viruses are not cells
tobacco mosaic virus
need host “machinery”
A package of genes in transit from one host cell to another
“A piece of bad news wrapped in protein”
– Peter Medawar
Linear or circular
envelopes are derived from host cell membrane
glycoproteins on surface
viral DNA/RNA takes over host
reprograms host cell to copy viral nucleic acid & build viral proteins
Self assembly
exit cell
kills cells by lysis
fever, aches, bleeding…
envelope proteins
between proteins on viral coat &
receptors on host cell surface
broad host range
narrow host range
human cold virus = only cells lining upper respiratory tract of humans
HIV = binds only to specific white blood cells
lambda phage
reproduce with bacteria
Bacteria have defenses against phages
bacterial mutants with receptors that are no longer recognized by a phage
natural selection favors these mutants
bacteria produce restriction enzymes
natural selection favors phage mutants resistant to bacterial defenses
When do
enzyme = reverse transcriptase
host’s RNA polymerase now transcribes viral DNA into viral mRNA
mRNA codes for viral components
host’s ribosomes produce new viral proteins
Why is this
capsid containing 2 RNA
strands & 2 copies of
high mutation rate
translated into viral proteins
released from cell by “budding” or by lysis
11% of Caucasians have mutant receptor allele
Block vRNA replication
CAF replication factor
hepatitis B virus
Cancer viruses
Transform cells into cancer cells after integration of viral DNA into host DNA
carry oncogenes that trigger cancerous characteristics in cells
version of human gene that normally controls cell cycle or cell growth
Stanley Prusiner
All known prion diseases are fatal. Since the immune system does not recognize prions as foreign, no natural protection develops. Scrapie in sheep was first described during the18th century. It has been transmitted to other animals such as mink and cats, and more recently to cows (mad cow disease or bovine spongiform encephalopathy, BSE) through contaminated feedstuff.
In New Guinea, the Fore-people contracted kuru by eating the brains of deceased people. Creutzfeldt-Jakob Disease (CJD) frequently arises spontaneously, while fatal familial insomnia (FFI) Gerstmann-Sträussler-Scheinker (GSS) disease, and 10-15% of CJD are caused by mutations in the gene encoding the prion protein. A new variant CJD, diagnosed in some 20 patients, may have arisen through transmission of BSE to humans.
AP Biology