Viruses & Bacteria

Chapter 19

I. VirusesQ: Is a virus living or nonliving?Viruses HAVE:

• DNA or RNA• Reproduce (only in living cells)

Viruses DO NOT HAVE:• Growth/development• Cells• Response to stimuli• Energy use

VIRUS = a NONLIVING particle of nucleic acid & a protein coat (capsid)

Viruses grouped based on…1) Shape

2) Having either RNA or DNA 3) The organism it infects

T4 virusRetrovirus

Chicken pox

Viral Reproduction• To reproduce, it needs a HOST CELL (a living cell) to infect.• Viruses only attach to certain cells – not all!

•Have 2 cycles: lytic & lysogenic

http://www.ptpleasantbch.k12.nj.us/bridge/genbio/microbiology.html

http://www.ptpleasantbch.k12.nj.us/bridge/genbio/microbiology.html

Which is potentially more dangerous – lytic or lysogenic viruses?

•Lysogenic viruses!

• Can spread w/o knowing it

Fighting Viral Fighting Viral InfectionsInfections

1. Vaccination • made from “dead”/weakened/altered pathogens• stimulates immune system to protect against that virus

2. Antibodies = proteins that help block/destroy pathogens

• made by white blood cells• creates memory to attack future virus exposure

HIV and HIV and AIDSAIDS

HIV = Human Immunodeficiency Virus

AIDS = Acquired Immune Deficiency Syndrome * HIV = virus that causes AIDS.

HIV & AIDS Info:• HIV is LYSOGENIC

• >42 mil. have died with HIV/AIDS

• 40,000 new infections found every year in U.S.; 50% in ages 25 or younger

• Most don’t die from AIDS – they die from another disease the immune system can’t fight off.

• HIV attacks & weakens immune system (kills helper T-cells) - unable to fight off certain infections.

Bacteria• Single-celled prokaryotes

•Living cells

•Many shapes and sizes

Structure of Bacteria1. DNA (circular, not in a nucleus)

2. Cytoplasm

4. Cell wall

3. Cell membrane

http://www.sirinet.net/~jgjohnso/typicalbacteria.html

How do bacteria reproduce?1. Binary fission –bacterium copies itself & divides into two

• asexual reproduction• makes identical bacteria

http://www.anselm.edu/homepage/jpitocch/genbio/binfission.JPG

Fighting Bacterial Fighting Bacterial InfectionsInfections

1. Antibiotics - compounds that block growth & reproduction of bacteria• If stop taking too

soon, not all bacteria get destroyed

• Antibiotic Resistance = remaining bacteria mutates & is unaffected by antibiotic2. Vaccination

3. Sterilization – using high heat to kill bacteria