1. Lab 17 on Thursday

2. Prokaryotes and Viruses
Chapter 25

3. Learning Objectives Describe prions and the diseases they cause
Describe general characteristics of Prokaryotes
Compare and contrast bacteria, archeae and eukarya
Compare and contrast gram positive and gram negative bacteria
Describe gram + and gram- bacteria
Describe the three main bacterial shapes

4. Why It Matters Prokaryotes: The smallest organisms
Figure 25.1 Bacillus bacteria on the point of a pin. Cells magnified (a) 70 times, (b) 350 times, and (c) 14,000 times.

5. Prions Infectious proteins with no associated nucleic acids
Misfolded versions of normal cellular proteins that can induce other normal proteins to misfold

6. Prion Diseases Degenerate nervous system in mammals
Scrapie: Brain disease in sheep
Mad cow disease (Bovine spongiform encephalopathy): Spongy holes and protein deposits in brain tissue
Creutzfeldt-Jakob disease: Rapid mental deterioration, loss of vision and speech, paralysis
Kuru-cannibalistic tribe in New Guinea,

7. Brain Tissue Damaged by BSE
Figure Bovine spongiform encephalopathy (BSE). The light-colored patches in this section from a brain damaged by BSE are areas where tissue has been destroyed.

8. 25.1 Prokaryotic Structure and Function
Prokaryotes are simple in structure compared with eukaryotic cells
Prokaryotes have the greatest metabolic diversity of all living organisms
Prokaryotes differ in whether oxygen can be used in their metabolism

9. 25.1 (cont.) Prokaryotes fix and metabolize nitrogen
Prokaryotes reproduce asexually or, rarely, by a form of sexual reproduction
In nature, bacteria may live in communities attached to a surface

10. Prokaryotes Colonize a great diversity of habitats
Are small but complex cells
Have great metabolic diversity
Adapt rapidly to their environments

11. Three Common Shapes in Prokaryotes
Spherical: cocci
Rodlike: bacilli
Spiral: vibrios (curved) and spirilla (helix)
Figure 25.2 Common shapes among prokaryotes. (a) Scanning electron microscope (SEM) image of Micrococcus, a coccus bacterium; (b) SEM of Salmonella, a bacillus bacterium; (c) SEM of Spiroplasma, a spiral prokaryote of the spirillum type.

13. Prokaryotic Genomes Prokaryotic chromosome Plasmids
Single, circular DNA molecule
Packaged into nucleoid
No nucleolus
No nuclear membranes
Plasmids
Small circles of DNA
Genes supplement nucleoid genes
Replicate independently (along with main DNA)

14. Folded DNA molecule (in the nucleoid) Cytoplasm containing ribosomes
Plasmid
Pili
Flagellum
Capsule
Figure 25.3 The structures of a bacterial cell.
Plasma
membrane
Peptido-
glycan layer
Outer
membrane
Cell wall
Fig. 25-3, p. 528

15. Prokaryotic Ribosomes
Bacterial ribosomes
Smaller than eukaryotic ribosomes
Protein synthesis similar to eukaryotes
Archaeal ribosomes
Size similar to bacteria
Different structure
Protein synthesis is combination of bacterial and eukaryotic processes

16. Prokaryotic Cell Wall Protects plasma membrane Made of peptidoglycans
Helps withstand osmotic pressure
Prevents action of detergent-like chemicals
Made of peptidoglycans
Polysaccharide polymers connected by short polypeptides

17. Gram Stain Gram stain technique Gram-positive bacteria
Stain with crystal violet, then with iodine
Fixes dye to cell wall
Wash with alcohol
Stain again with fuchsin or safranin
Gram-positive bacteria
Appear purple because crystal violet retained
Gram-negative bacteria
Appear pink because crystal violet lost

18. Gram-Positive Bacteria
Single, relatively thick peptidoglycan layer
Figure 25.4 Cell wall structure in Gram-positive and Gram-negative bacteria. (a) The thick cell wall in Gram-positive bacteria. (b) The thin cell wall of Gram-negative bacteria.

19. a. Gram-positive bacterial cell wall
Capsule
may be
present
a. Gram-positive bacterial cell wall
Peptidoglycan layer
Cell
wall
Plasma membrane
Figure 25.4 Cell wall structure in Gram-positive and Gram-negative bacteria. (a) The thick cell wall in Gram-positive bacteria. (b) The thin cell wall of Gram-negative bacteria.
Cytoplasm
Fig. 25-4, p. 529

20. Gram-Negative Bacteria
Two-layered walls; relatively thin peptidoglycan sheath surrounded by outer membrane
Figure 25.4 Cell wall structure in Gram-positive and Gram-negative bacteria. (a) The thick cell wall in Gram-positive bacteria. (b) The thin cell wall of Gram-negative bacteria.

21. b. Gram-negative bacterial cell wall
Capsule
Outer membrane
Peptidoglycan layer
Cell wall
Plasma membrane
Figure 25.4 Cell wall structure in Gram-positive and Gram-negative bacteria. (a) The thick cell wall in Gram-positive bacteria. (b) The thin cell wall of Gram-negative bacteria.
Cytoplasm
Fig. 25-4, p. 529

22. Slime Coat Capsule Slime attached to cells Slime layer
Loosely associated with cells
Protects bacteria from desiccation, antibiotics, viruses, antibodies, and enzymes
Helps bacteria adhere to surfaces

23. Pili Rigid protein shafts extend from cell walls
Mostly in Gram-negative bacteria
Help bacteria attach to each other or to surfaces
Figure 25.7 Pili extending from the surface of a dividing E. coli bacterium.

24. Obtaining Carbon and Energy (1)
Autotrophs (auto = self; troph = nourishment)
Use carbon dioxide as their carbon source
Heterotrophs
Obtain carbon from organic molecules

25. Obtaining Carbon and Energy (2)
Chemoautotrophs
Obtain energy by oxidizing inorganic or organic substances
Phototrophs
Use light as energy source

26. Oxidation of molecules Light
Energy source
Oxidation of molecules
Light
CHEMOAUTOTROPH
PHOTOAUTOTROPH
CO2
Found in some bacteria
and archaeans; not
found in eukaryotes
Found in some photo-synthetic bacteria, in
some protists, and
in plants
Carbon source
CHEMOHETEROTROPH
PHOTOHETEROTROPH
Figure 25.8 Modes of nutrition among Bacteria and Archaea. All four modes of nutrition occur in the Bacteria with chemoheterotrophs as the most common type; among the Archaea, chemo-autotrophs are most common, while others are chemoheterotrophs.
Organic molecules
Include some bacteria
and archaeans, and
also in protists, fungi,
animals, and plants
Found in some
photosynthetic
bacteria
* Inorganic molecules for chemoautotrophs
and organic molecules for chemoheterotrophs.
Fig. 25-8, p. 531

27. Prokaryotes and Oxygen: Aerobes
Require oxygen for cellular respiration
Oxygen is the final electron acceptor
Obligate aerobes
Cannot grow without oxygen

28. Prokaryotes and Oxygen: Anaerobes
Do not require oxygen to live
Obligate anaerobes (poisoned by oxygen)
Use fermentation or type of respiration in which inorganic molecules (NO3– or SO42–) are final electron acceptors
Facultative anaerobes
Use O2 when present
Use fermentation under anaerobic conditions

29. Prokaryotes and Nitrogen (1)
Nitrogen fixation
Conversion of atmospheric nitrogen (N3) to ammonia (NH3)
Ammonia ionized to ammonium (NH4+) for biosynthesis
Nitrogen-fixing bacteria include
Some cyanobacteria
Free-living Azotobacter
Bacteria such as Rhizobium that are symbiotic with plants

30. Prokaryotes and Nitrogen (2)
Nitrification
Conversion of ammonium (NH4+) to nitrate (NO3–)
Two-step conversion by nitrifying bacteria
Some types of bacteria convert ammonia to nitrite (NO2–)
Other types convert nitrite to nitrate

31. Prokaryote Reproduction
Binary fission
Asexual reproduction
Produces exact copies of parent
Conjugation
Two cells connected by pilus
Part of DNA of one cell is transferred to another cell (usually plasmids)

32. Endospore
Develops inside some bacteria when environmental conditions are unfavorable
Metabolically inactive
Highly resistant to heat, desiccation, attack by enzymes or chemicals

33. Endospore: Clostridium tetani
Figure 25.9 A developing endospore of the bacterium Clostridium tetani, a dangerous pathogen that causes tetanus.

34. 25.2 Domain Bacteria
Molecular studies reveal more than a dozen evolutionary branches in the Bacteria
Bacteria cause diseases by several mechanisms
Pathogenic bacteria commonly develop resistance to antibiotics

35. Classification of Prokaryotes
Figure An abbreviated phylogenetic tree of prokaryotes.

36. Bacteria 12 separate evolutionary branches Six most important groups:
Proteobacteria
Green bacteria
Cyanobacteria
Gram-positive
Spirochetes
Chlamydias

37. The Proteobacteria (1) Gram-negative bacteria
Purple sulfur (photoautotrophic)
Purple nonsulfur (photoheterotrophic)
Purple photosynthetic pigment
Free-living proteobacteria (chemoheterotrophs)
Some cause human diseases
Bubonic plague, Legionnaire’s disease, gonorrhea, gastroenteritis, dysentery
Some plant pathogens
Rot, scabs, wilts

38. The Cyanobacteria Gram-negative photoautotrophs Blue-green color
Photosynthesis similar to plants
Release oxygen as byproduct of photosynthesis
Figure Cyanobacteria. (a) A population of cyanobacteria covering the surface of a pond. (b) and (c) Chains of cyanobacterial cells. Some cells in the chains form spores. The hetero-cyst is a specialized cell that fi xes nitrogen.

39. b. Heterocyst Resting spore c. Fig. 25-13, p. 535
Figure Cyanobacteria. (a) A population of cyanobacteria covering the surface of a pond. (b) and (c) Chains of cyanobacterial cells. Some cells in the chains form spores. The hetero-cyst is a specialized cell that fi xes nitrogen.
Fig , p. 535

40. The Gram-Positive Bacteria (1)
Primarily chemoheterotrophs
Many pathogenic species
Anthrax
Staphylococcus
Food poisoning, skin infections, toxic shock syndrome, pneumonia, meningitis
Streptococcus
Strep throat, pneumonia, scarlet fever, kidney infections
Figure Streptococcus bacteria forming the long chains of cells typical of many species in this genus.

41. The Gram-Positive Bacteria (2)
Some beneficial species
Lactobacillus
Lactic acid fermentation used to produce pickles, sauerkraut, yogurt
Mycoplasmas
Naked cells that have lost their cell walls
Smallest known cells (0.1 to 0.2 µm in diameter)

42. The Spirochetes Gram-negative spiral-shaped bacteria
Propelled by rotation of flagella
Enables movement in thick mud and sewage
Beneficial or harmless species
Spirochetes in termite intestine digest plant fiber
Treponema in mouth
Pathogenic species
Syphilis, relapsing fever, Lyme disease

43. The Chlamydias Gram-negative bacteria
Cell walls with membrane outside
Lack peptidoglycans
Intercellular parasites that cause diseases in animals
Figure Cells of Chlamydia trachomatis inside a human cell. This bacterium is a major infectious cause of human eye and genital disease.

44. Bacterial Disease Mechanisms
Exotoxins
Toxic proteins leaked or secreted
Clostridium botulinum (botulism exotoxin)
Endotoxins
Toxins only released when bacteria die or lyse
E. coli, Salmonella, Shigella
Exoenzymes
Enzymes secreted that digest plasma membrane
Streptococcus, Staphylococcus, Clostridium

45. Resistance to Antibiotics
Pathogenic bacteria may develop resistance to antibiotics
Mutation of their own genes
Acquiring resistance genes from other bacteria
Resistant strains difficult to treat with conventional antibiotics
Resistance is a form of evolutionary adaptation

46. 25.3 Domain Archaea Archaea have some unique characteristics
Molecular studies reveal three evolutionary branches in the Archaea

47. The Archaea
Archaea are more closely related to domain Eukarya than domain Bacteria
Characteristics
Some features like bacteria
Some features like eukaryotes
Some unique features

48. Characteristics of Bacteria, Archaea, and Eukarya