Presentation on theme: "Prokaryotes Chapter 27. Earliest organisms on Earth - evolved alone for 1.5 billion years. More prokaryotes inhabit a handful of fertile soil or the mouth."— Presentation transcript:
Prokaryotes Chapter 27
Earliest organisms on Earth - evolved alone for 1.5 billion years. More prokaryotes inhabit a handful of fertile soil or the mouth or skin of a human than the total number of people who have ever lived.
The vivid reds, oranges, and yellows that paint these rocks are colonies of prokaryotes.
Types of diseases caused by bacteria - tuberculosis, cholera, many sexually transmissible diseases, certain types of food poisoning.
Most bacteria benign or beneficial. Bacteria in intestines produce vitamins. Prokaryotes recycle carbon, other elements between soil and atmosphere.
Mitochondria, chloroplasts evolved from prokaryotes - became residents in host cells.
2 prokaryotic domains (above kingdom): Bacteria and Archaea Archaea inhabit extreme environments - differ from bacteria in structural, biochemical, and physiological characteristics.
Most prokaryotes - unicellular. Some aggregate for period of time or form colonies. Shapes - spheres (cocci), rods (bacilli), helices (spirochetes).
Cell wall maintains shape, physical protection, prevents cell from bursting. Most bacterial cell walls contain peptidoglycan, (polymer of sugars and polypeptides) Archaea lack peptidoglycan.
Gram stain - identifies bacteria based on differences in cell walls. Gram + have simpler cell walls, large amounts of peptidoglycans.
Gram - have more complex cell walls, less peptidoglycan - outer membrane contains carbohydrates bonded to lipids. More threatening than gram- positive species.
Gram-negative bacteria more resistant to antibiotics - outer membrane impedes entry of antibiotics.
Many prokaryotes secrete sticky protective layer - capsule. Glue together cells of prokaryotes that live as colonies.
Pili fastens pathogenic bacteria to mucous membranes of host. Some specialized for holding 2 prokaryote cells together to transfer DNA during conjugation.
Most common form of movement - flagella. 2 nd found in spirochetes - filaments - moves like a corkscrew. 3 rd occurs in cells that secrete slimy threads - glides along at growing end of threads.
Capable of taxis (chemotaxis, phototaxis)
Prokaryotic cells lack nucleus, internal compartments bounded by membranes like eukaryotes. Use infolded regions of plasma membrane to perform metabolic functions (cellular respiration, photosynthesis)
Simpler genomes than eukaryotes - DNA concentrated as fibers in nucleoid region. Single prokaryotic chromosome - double-stranded DNA molecule in form of ring. May also have smaller rings of DNA (plasmids) consist of only a few genes.
Prokaryotes reproduce asexually - binary fission. Transformation - cell can absorb, integrate fragments of DNA from environment. Conjugation - directly transfers genes to another cell. Transduction - viruses transfer genes between prokaryotes.
Prokaryote can withstand harsh conditions. Bacteria form resistant cells - endospores - cell replicates chromosome, surrounds one chromosome with durable wall. Can survive lack of nutrients and water, extreme heat or cold, and most poisons.
When conditions favorable - hydrates and becomes active. Microorganisms release antibiotics to inhibit growth of other microorganisms (prokaryotes, protists, and fungi) because of competition for space. Humans use these to kill bacteria.
Prokaryotes grouped according to how they obtain nutrition. 1 Light energy - phototrophs. 2 Energy from chemicals in environment -chemotrophs. 3 Need only CO 2 as carbon source - autotrophs. 4 Require organic nutrient as carbon source - heterotrophs.
Further divided based on what they use. 1 Photoautotrophs - photosynthetic - light energy to synthesize organic compounds from CO 2. Photoautotrophic prokaryotes - cyanobacteria. Photosynthetic eukaryotes - plants and algae.
2 Chemoautotrophs need CO 2 as carbon source, obtain energy by oxidizing inorganic substances, not light - i.e. hydrogen sulfide (H 2 S), ammonia (NH 3 ) Unique to prokaryotes. 3 Photoheterotrophs - light to generate ATP, obtain carbon in organic form. Restricted to prokaryotes.
4 Chemoheterotrophs must consume organic molecules for energy and carbon. Found in prokaryotes, protists, fungi, animals, and even some parasitic plants. Majority of prokaryotes - chemoheterotrophs. Include saprobes (decomposers) and parasites.
O 2 also has impact. Obligate aerobes require O 2 for respiration. Facultative anerobes will use O 2 if present; can also grow by fermentation in anaerobic environment. Obligate anaerobes are poisoned by O 2 use either fermentation or anaerobic respiration.
1 st prokaryotes - heterotrophic - fed on primordial soup - depleted supply of organic molecules in environment. Natural selection favored prokaryote that could harness energy of sunlight make ATP. Photosynthesis probably evolved once and was lost by heterotrophs.
Atmosphere transformed from reducing one to oxidizing one by evolution of cyanobacteria. Cellular respiration probably evolved by modification of photosynthetic equipment for new function (both use electron transport chain).
Survey of Prokaryotes Archaea - extremophiles, “lovers” of extreme environments. 1 Methanogens - obtain energy by using CO 2 to oxidize H 2 replacing methane as waste - live in swamps and marshes, guts of animals. May contribute to global warming.
2 Extreme halophiles - saline places - Great Salt Lake, Dead Sea. Colonies form purple-red scum from photosynthetic pigment similar to pigment found in human retina.
3 Extreme thermophiles - hot environments - optimum temperatures for most - 60 o C-80 o C. One sulfur-metabolizing thermophile lives at 105 o C water near deep-sea hydrothermal vents.
Why important? Decomposers - important to nutrient recycling. Nitrogen fixation - important to nitrogen cycle. Many - symbiotic - involved in mutual relationship with host - i.e. - fish provides bioluminescent bacteria under eye with organic materials uses flashlight to lure prey, signal potential mates.
Most of the time our defenses check growth of pathogens. Pathogenic prokaryotes cause half of all human disease when internal defenses cannot fight them off.
Some pathogens - opportunistic (always in our system) - attack only when defenses down. Robert Koch 1 st to connect certain diseases to specific bacteria - established Koch’s postulates. Ensures that pathogen really is causing the disease.
Pathogens can cause illness by producing poisons - exotoxins and endotoxins. Exotoxins are proteins secreted by prokaryotes - can produce disease symptoms even if prokaryote not present. Endotoxins - components of outer membranes of some gram-negative bacteria. Common in food poisoning.
Disease control mostly due to education, not to expansion of drugs. Overuse of antibiotics has led to evolution of new strains of bacteria. Biological warfare also still a threat. Humans use prokaryotes to treat biological issues, such as oil spills.