1. Chapter 20 Viruses and Bacteria

2. 20.1 Viruses

4. The Discovery of Viruses
In 1935, American biochemist Wendell Stanley isolated crystals from he tobacco mosaic virus.
Living organisms do not crystallize
Virus – a nonliving particle made of proteins, nucleic acids, and sometimes lipids
Can only reproduce by infecting living cells

5. Structure and Composition
The protein coat surrounding a virus is called a capsid.
To enter the host cell, most viruses have proteins on their capsid to “trick” the cell to take in the virus.
Once inside virus replicates and destroys the cell.
Virus must bind to a specific protein on host cell, therefore they only infect a specific cell.
Plant viruses infect plant cells
Animal viruses infect animal cells
Bacteriophages infect bacteria

6. Life Cycle of a Virus Virus attached to host cell
Chromosome-like part enters cell
Chromosome-like part takes over cell
Virus changes the hereditary material in the host cell so that the host cell produces more viruses
Cell breaks open-releases new virus-invade other cells
Tissue damage and disease result
Polio, mumps, rabies, and flu

7. A Closer Look at RNA Viruses
About 70% of viruses contain RNA (Ribonucleic acid) rather than DNA (Deoxyribonucleic acid).
The Common Cold
Capsid settles on a cell (typically in your nose), goes into cell, viral protein makes copies of viral RNA. Your cell’s ribosomes mistake the viral RNA for your RNA and make more viral proteins. Within 8 hours, hundreds of new virus particles are released.

8. Viruses and Disease
Despite their small size, viruses cause many serious diseases.
AIDS – a viral disease that destroys the body’s immune system
People with AIDS die from diseases most others can resist.
Spread:
Sex
Blood products
Sharing contaminated needles
Pregnant woman to baby

10. 20.2 Prokaryotes

11. Classifying Prokaryotes
Prokaryotes – unicellular organisms that lack a nucleus.
Classified into two groups: Bacteria and Archaea
Bacteria (Kingdom Eubacteria) – wide range of organisms
Live in fresh water, salt water, on land, in animal bodies
E. coli
Archaea (Kingdom Archaebacteria)– DNA more like those of eukaryotes
Live in extreme conditions – little or no oxygen (digestive tracts), hot springs, extremely salty environments,

12. Structure and Function
Shapes:
Bacilli – rod-shaped
Cocci – spherical shaped
Spirilla – spiral and cork-shaped
Growth, Reproduction, and Recombination
Binary Fission – Prokaryote replicates DNA and divides in half, producing two identical cells.
Some can divide as often as every 20 minutes
Endospore – A thick internal wall that encloses the DNA and portion of the cytoplasm when growth conditions are not favorable.

14. Mutations – main way prokaryotes evolve
Random changes in DNA then inherited by daughter cells
Conjugation – the way prokaryotes exchange genetic information.
A hollow bridge forms between two bacterial cells, and genetic information moves from one cell to another.

15. The Importance of Prokaryotes
Decomposers – break down dead organisms and return nutrients to soil
Essential in wastewater treatment process
Producers – Tiny cyanobacterium Prochlorococcus most abundant photosynthetic organism in the world.
Nitrogen fixers – only prokaryotes can convert nitrogen into a useable form.
Bacterium Rhizobium grows in nodules on the roots of legumes, such as soybean.
Covert nitrogen gas into useable form for plant

16. 20.3 Diseases Caused by Bacteria and Viruses

17. Bacterial Diseases Pathogens – organisms that cause disease.
Disease mechanisms – bacteria can cause disease by destroying living cells or by releasing chemicals that upset homeostasis.
Damaging host tissue – MRSA – staph infection – “flesh-eating” bacteria
Releasing toxins – diphtheria and botulism– caused by release of toxin

18. Controlling bacteria –
Physical Removal – washing hands and surfaces doesn’t kill, but helps to remove
Disinfectants – chemical solutions to kill bacteria
Food storage – low temperatures slow growth of bacteria
Food processing – boiling, steaming, and frying can sterilize food by increasing temperature until bacteria is killed
Sterilization by heat – sterilization of objects, such as medical instruments, well about 100 degrees Celsius
Preventing bacterial diseases
Vaccine – a preparation of weakened or killed pathogens or inactivated toxins. Prompts body to produce immunity.
Treating bacterial diseases
Antibiotics – block growth and reproduction of bacteria

19. Viral Diseases
Viruses attack and destroy certain cells of the body, sometimes even leading to cancer
Human papillomavirus (HPV) – genital warts – can also lead to cancer
Preventing viral diseases – vaccinations, personal hygiene
Treating viral diseases – Unlike bacteria, they cannot be treated with antibiotics
Antiviral medicines – attack viral enzymes
Tamiflu

20. Emerging Diseases
An unknown disease that appears in a population for the first time or a well-known disease that suddenly becomes harder to control.
Threaten human health because humans have little or no resistance to them, and because method of control have yet to be developed.
“Superbugs” – the widespread use of antibiotics has led to a process of natural selection that favors the emergence of resistance to these powerful drugs.
MRSA – Methicillin-resistant Staphylococcus aureus
Prions – protein infectious particles
Proteins found in normal cells are improperly folded. Damage nervous system.
Mad Cow Disease – Bovine Spongiform Encephalopathy

22. E. coli
Salmonella
Staphylococcus aureus

23. What is a virus?
What are the 6 steps in the life cycle of a virus?
What is AIDS?
What is an organism that lacks a nucleus?
What are the three shapes of bacteria?
What is binary fission?
What is conjugation?
Name one importance of prokaryotes.
What is a pathogen?
Do antibiotics kill viruses or bacteria?
What is an emergent disease?
Give one example of a superbug.