KEY CONCEPT Infections can be caused in several ways.

1. KEY CONCEPTInfections can be caused in several ways.

2. Viruses, bacteria, viroids, and prions can all cause infection. • Any disease-causing agent is called a pathogen. 1 nanometer (nm) = one billionth of a meter 100 nm eukaryotics cells10,000-100,000 nm viroids5-150 nm viruses50-200 nm prokaryotics cells200-10,000 nm prion2-10 nm

3. A virus is made of DNA or RNA and a protein coat. • non-living pathogen • can infect many organisms • A viroid is made only of single-stranded RNA. • causes disease in plants • passed through seeds or pollen

4. causes misfolding of other proteins • results in diseases of the brain • A prion is made only of proteins.

5. KEY CONCEPT Viruses exist in a variety of shapes and sizes.

6. capsid surfaceproteins nucleic acid nucleic acid capsid Surface proteins lipidenvelope capsid nucleic acid surfaceproteins lipid envelope Viruses differ in shape and in ways of entering host cells. • Viruses have a simple structure. • genetic material • capsid, a protein shell • maybe a lipid envelope, a protective outer coat enveloped(influenza) helical(rabies) polyhedral(foot-and-mouth disease)

7. capsid DNA tail sheath tail fiber • Bacteriophages infect bacteria.

8. colored SEM; magnifications: large photo 25,000; inset 38,000x • bacteriophages pierce host cells • Viruses enter cells in various ways.

9. Viruses enter cells in various ways. • viruses of eukaryotes enter by endocytosis

10. Viruses enter cells in various ways. • viruses of eukaryotes also fuse with membrane

11. host bacterium The bacterophage attachesand injects it DNA into a host bacterium. The host bacterium breaks apart, or lyses. Bacteriophages are ableto infect new host cells. The viral DNA forms a circle. The viral DNA directs the hostcell to produce new viral parts.The parts assemble into newbacteriophages. The virus may enter the lysogenic cycle, in which the host cell is not destroyed. Viruses cause two types of infections. • A lytic infection causes the host cell to burst.

12. The prophage may leave the host’s DNA and enter the lytic cycle. The viral DNA is called a prophage when it combines with the host cell’s DNA. Although the prophage is not active, it replicates along with the host cell’s DNA. Many cell divisions produce a colony of bacteria infected with prophage. • A lysogenic infection does no immediate harm.

13. KEY CONCEPT Some viral diseases can be prevented with vaccines.

14. Viruses cause many infectious diseases • There are many examples of viral infections. • common cold

15. Viruses cause many infectious diseases • influenza • There are many examples of viral infections. • common cold

16. Viruses cause many infectious diseases • influenza • There are many examples of viral infections. • common cold • SARS

17. HIV-infected white blood cell Viruses cause many infectious diseases • HIV • There are many examples of viral infections. • The body has natural defenses against viruses.

18. Vaccines are made from weakened pathogens. • A vaccine stimulates the body’s own immune response. • Vaccines prepare the immune system for a future attack. • Vaccines are the only way to control the spread of viral disease.

19. KEY CONCEPT Bacteria and archaea are both single-celled prokaryotes.

20. Prokaryotes are widespread on Earth. • Prokaryotes can be grouped by their need for oxygen. • obligate anaerobesare poisoned byoxygen • obligate aerobes need oxygen • facultative aerobes can live with or without oxygen

21. Lactobacilli: rod-shaped Spirochaeta: spiral Enterococci: spherical Bacteria and archaea are structurally similar but have different molecular characteristics. • Bacteria commonly come in three forms. • rod-shaped, called bacilli • spiral, called spirilla or spirochetes • spherical, called cocci • Archaea have many shapes.

22. pili plasmamembrance flagellum chromosome cell wall plasmid This diagram shows the typical structure of a prokaryote. Archaea and bacteria look very similar, although they have important molecular differences. • plasmid • flagellum • pili • Bacteria and archaea have similar structures.

23. GRAM NEGATIVE GRAM POSITIVE • The amount of peptidoglycan within the cell wall can differ between bacteria • Bacteria and archaea have molecular differences. • Archaea have different lipids entirely

24. Gram-negative bacteria have a thin layer of peptidoglycan and stain red. Gram-positive bacteria have a thicker peptidoglycan layer and stain purple. • stains polymer peptidoglycan • gram-positive stains purple, more peptidoglycan • gram-negative stains pink, less peptidoglycan • Gram staining identifies bacteria.

25. conjugation bridge TEM; magnification 6000x Bacteria have various strategies for survival. • Prokaryotes exchange genes during conjugation. • Bacteria may survive by forming endospores.

26. KEY CONCEPTProkaryotes perform important functions for organisms and ecosystems.

27. Prokaryotes provide nutrients to humans and other animals. • Prokaryotes live in digestive systems of animals. • make vitamins • break down food • fill niches

28. yogurt, cheese • Bacteria help ferment many foods. • pickles, sauerkraut • soy sauce, vinegar

29. Prokaryotes play important roles in ecosystems. • Prokaryotes have many functions in ecosystems. • photosynthesize • recycle carbon, nitrogen,hydrogen, sulfur • fix nitrogen

30. Bioremediation uses prokaryotes to break down pollutants. • oil spills • biodegradable materials