Prokaryotes

1. Prokaryotes

4. Structure, function, and reproduction of prokaryotes • Most prokaryotes are unicellular.  • Some species form aggregates of two or more individuals. • Three (3) common shapes:  cocci (round); bacilli (rod); helical (spiral) • Prokaryotes are typically 1-5 μm in diameter, but some can be seen by the naked eye. • - Eukaryotic cells are typically 10-100 μm in diameter.The largest known prokaryote is .5mm in length

7. Almost all prokaryotes have cell walls external to the plasma membrane. 1.  Cell walls maintain cell shape. 2.  Cell walls are composed of peptidoglycan. Protect the cell Prevent cell from bursting in a hypotonic environment

8. There are two types of cell walls.  Bacteria are grouped according to cell wall type.  a.  Gram-positive bacteria have simple, thick cell walls.  Their cell walls are composed of a relatively large amount of peptidoglycan. b.  Gram-negative bacteria have less peptidoglycan and are more complex.  They have a peptidoglycan layer surrounded by the plasma membrane and an outer membrane.    - Gram-negative bacteria are typically more resistant to host immune defenses and antibiotics. Note that the two types of bacteria can be stained to determine which is gram-negative (pink) and gram-positive (purple) using a Gram Stain.

10. Peptidoglycan Plasma membrane Lipopolysaccharide layer Outer membrane Peptidoglycan Plasma membrane Gram Positive Gram Negative

11. Most prokaryotes secrete sticky substances that form a protective layer and enable them to adhere to substrates The sticky protective layer secreted by prokaryotes is called the capsule. Some prokaryotes adhere to substrates using pili.  Some pili are specialized for DNA transfer. This process is called conjugation; note for later in class.

16. Cellular and genomic organization of prokaryotes is different from that of eukaryotes 1.  Prokaryotes have no nucleus. 2.  The nucleoidregion in a prokaryotic cell consists of a concentrated mass of DNA. This mass of DNA is usually one thousand times less than what is found in a eukaryote. 3.  A prokaryote may have a plasmid in addition to its major chromosome.  A plasmid is a small ring of DNA that carries accessory genes. Usually these genes are for antibiotic resistance!

17. Asexual reproduction: Fission

18. Specialized membranes of prokaryotes

19. Prokaryotes grow and adapt rapidly- The doubling time for E. coli is 20 minutes.  Start with one E. coli cell.  After 48 hours of doubling every 20 minutes, the mass of E. coli would be 10,000 times the mass of the earth. Bacteria do not have gene transfer by sexual reproduction, but do transfer genes. Why? This is an aid in adapting (evolving). 1.  Three (3) ways for genes to be transferred between cells: a.  Transformation – cell takes up genes from the surrounding environment. b.  Conjugation – direct transfer of genes from one prokaryote to another. Use the sex pilus to conjugate. c.  Transduction – viruses transfer genes between prokaryotes.

20. Prokaryotic conjugation Pilus

21. Endospores are resistant cells formed by some bacteria as a way to withstand harsh conditions. The cell replicates its chromosome and wraps it in a durable wall that can protect the chromosome from adverse conditions, e.g. boiling water, desiccation. When the environment is good again, the cell will revive to a new vegetative (growing) spore.

23. Nutritional and metabolic diversity • All prokaryotes (and eukaryotes too) are grouped into four (4) categories according to how they obtain energy and carbon. • 1.  Photoautotrophs • - Photosynthetic à use light as the energy source •                                     - CO2 is the carbon source • Example:  Cyanobacteria; plants (eukaryotic).

24. One of the most independent organisms on earth: Cyanobacteria (Anabaena)

25. Cyanobacteria: Gloeothece (top left), Nostoc (top right), Calothrix (bottom left), Fischerella (bottom right)

26. A bloom of cyanobacteria

27. Microcystis Anabaena Algal blooms

28. 2.  Chemoautotrophs      - Energy from oxidation of inorganic substances (e.g. NH4, and S)      - CO2 is the carbon source        Example:  Sulfolobus, Beggiatoa (shown on slide)

30. 3.  Photoheterotrophs      - Light as energy source      - Organic compounds are source of carbon 4.  Chemoheterotrophs       - Organic compounds are energy source and source of carbon (this includes humans) Examples:  Many prokaryotes; animals (eukaryotic); fungi (eukaryotic)

32. Metabolic relationships to oxygen 1.  Obligate aerobes       - Use O2 for respiration; cannot grow without it. (Humans are obligate aerobes) 2.  Facultative aerobes       - Use O2 when available; ferment when O2 isn’t available. 3.  Obligate anaerobes       - Poisoned by O2; use fermentation or live by anaerobic respiration.  In anaerobicrespiration, inorganic molecules like SO4, NO3, and Fe3+ are used instead of oxygen.

37. Rhizobium: N2-Fixing, Lives in Plant Roots of Legumes

38. Heliobacter: Causes stomach ulcers

39. Chlamydias - Parasitic; survive only within cells of animals  - Some cause STDs e.g.chlamydia

40. Spirochetes       - Helical heterotrophs      - Some cause STDs e.g. syphilis

41. Gram-Positive Bacteria        - Broad, diverse group          - Antibiotic producing bacteria are in this group - Example shown is Streptomyces (streptomycin) - And (next slide)

42. Mycoplasma shown covering a human cell; some species of mycoplasmas cause walking pneumonia

43. Cyanobacteria          - Oxygenic photosynthesis, and chloroplasts evolved from them.

44. Ecological impacts of prokaryotes  A.  Prokaryotes are links in the recycling of chemical elements B.  Many prokaryotes are symbiotic (2 organisms living in direct contact with each other). There are three types of symbioses: 1.  Mutualism – both symbiotic organisms benefit                          - e.g. Nitrogen-fixing bacteria like Rhizobium: plant obtain organic nitrogen, Rhizobium gets energy in the form of sugars that the plant produces.

45. 54.18 The nitrogen cycle

46. 2.  Commensalism – one organism benefits and the other is not harmed. - e.g. Bacteria on our skin 3.  Parasitism – parasite benefits and the host is harmed. C.  Pathogens cause human diseases - Some pathogens are opportunistic.  They may be normal residents of the host, but if the host is weakened, then they cause disease.

47. Lyme disease: Caused by a spirochete

48. Red-band disease (RBD) consists of a narrow band of filamentous cyanobacteria that advances slowly across the surface of a coral, killing living tissue as it progresses.

49. How do we know if a particular organism is responsible for a disease? Robert Koch formed postulates as guidelines to establish that a disease is caused by a particular pathogen: a.  Find same pathogen in each diseased individual. b.  Isolate the pathogen and grow it in pure culture. c.  Inoculate an individual with the isolated pathogen and the disease is induced. d.  Isolate the same pathogen from the infected individual. This procedure is called Koch’s Postulates and is used widely to determine what infectious agent causes disease.

50. Most pathogens cause disease by producing poisons, these are either: • Exotoxins: proteins secreted by bacterial cells • Can cause disease without the organism itself being present; toxin is enough • Among the most potent poisons known • Botulism • Cholera • Endotoxins:toxic component of some gram negative bacteria.  (e.g. bacterium’s outer membrane- lipopolysaccharide)