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Chapter 27

Chapter 27



AP Biology Lecture

AP Biology Lecture
Monday, January 26



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    Chapter 27 Chapter 27 Presentation Transcript

    • Chapter 27 Prokaryotes and the Origins of Metabolic
    • I. They’re almost everywhere
      • A. Outnumber all eukaryotic organisms combined
      • 1. Flourish in all habitats
      • 2. Many live in symbiotic relationships
    • B. Bacteria and archaea are the two main branches of prokaryotic evolution
      • Bacteria and archaea used to be grouped as Monerans
      • Now use a two Domain approach (taxonomic group above Kingdom )
      • 3. Molecular studies indicate that Domain Archaea and Domain Bacteria diverged first and that Domain Archaea and Eukarya share a more recent common ancestor
      • Universal common Ancestor
      Bacteria Archaea Eukarya
    • A Comparison of the Three Domains of Life Present Present Present Nuclear membrane Eukarya Archaea Bacteria
    • Present Absent Absent Membrane-enclosed organelles Eukarya Archaea Bacteria
    • Absent Absent Present Peptidogylcan in cell wall Eukarya Archaea Bacteria
    • Several kinds Several kinds One kind RNA polymerase Eukarya Archaea Bacteria
    • Methionine Methionine Formyl-methionine Initiator amino acid for start of protein synthesis Eukarya Archaea Bacteria
    • Present Present in some genes Absent Introns Eukarya Archaea Bacteria
    • Growth not inhibited Growth not inhibited Growth inhibited Response to antibiotics and streptomycin and chloramphenicol Eukarya Archaea Bacteria
      • 4. Archaea are found in extreme habitats reminiscent of early earth and are referred to as:
      • Thermophiles —thrive in very hot temperatures
      • Halophiles —thrive in highly saline environments like the Dead Sea
      • Methanogens —release methane gas as a by-product of oxidizing hydrogen for energy
    • C. Nearly all prokaryotes have cell walls external to their plasma membranes
      • 1. Cell walls of bacteria contain peptidoglycan , a matrix of polymers of sugars cross-linked by short polypeptides.
      • 2. Gram stain is an important tool for identifying bacteria as “gram positive” (bacteria with walls containing a thick layer of peptidoglycan) or gram negative (bacteria with more complex walls including an outer liposaccharide membrane)
      • 3. Gram negative bacteria are more pathogenic than gram positive because their liposaccharides may be toxic .
      • 4. Outer membrane protects gram negative bacteria from hosts’ defenses and from antibiotics .
      • 5. Many prokaryotes secrete a sticky capsule outside the cell wall that serves as protection and a glue for adhering to a substratum
      • 6. Some may attach by appendages called pili which may be specialized to hold bacteria together during conjugation .
    • D. Most prokaryotes are motile
      • 1. Many have flagella: either several scattered over the cell surface or concentrated at one or both ends
      • 2. These flagella are different from eukaryotic flagella
    • E. The cellular and genomic organization of prokaryotes is fundamentally different from that of eukaryotes
      • 1. No membrane bound organelles
      • 2. DNA is circular , double-stranded and found in region called the nucleoid
      • 3 . Contains one thousandth of the DNA of a eukaryote
      • 4. Smaller rings of DNA called plasmids may carry genes for antibiotic resistance or metabolism of unusual nutrients
      • plasmids reproduce independently
      • may be transferred between bacteria during conjugation
    • F. Populations grow and adapt rapidly
      • 1. Divide asexually by binary fission (much less complicated than mitosis )
      • 2. Methods of genetic recombination
      • transformation --the uptake of genes from the environment
      • conjugation --the direct transfer of genetic material from one bacterium to another
      • transduction --the transfer of genes by a virus
      • 3. Mutations are the major source of genetic variation
      • Generation times may be as short as 20 minutes or as long as 3 hours.
      • 5. Growth stops as a result of exhaustion of nutrients or the toxic accumulation of wastes
      • 6. Some bacteria form endospores , which are tough-walled cells that can resist even boiling water
    • Cell shape
      • Can be spherical (coccus),
      • rods (bacillus),
      • Or helices (spirilla)
    • Cell size
      • 1-5 micrometers in diameter; 1/10 the size of eukaryotic cells
    • Cell surface
      • Cell wall of peptidoglycan which maintains shape, provides physical protection and prevents the cell from bursting in a hypotonic environment
    • Motility
      • Flagella—cause bacteria to spiral and corkscrew
    • Internal Membranes
      • Infoldings of plasma membrane used in respiration; cyanobacteria have thylakoid membranes used in photosynthesis
    • Genome
      • 1 Circular chromosome; may have both “F” and “R” plasmids
    • Reproduction and Growth
      • Binary fission which results in rapid geometric growth
      • Some bacterial genetic recombination is the result of transduction or conjugation in addition to mutation
    • II. Great diversity of Nutritional and metabolic adaptations: all organisms can be classified by how they obtain their energy and organic carbon compounds
      • A. Photoautotrophs— photosynthetic organisms that capture light from the sun but require carbon dioxide to make organic compounds. Cyanobacteria are prokaryotes that are phototrophs.
      • B. Chemoautotrophs—organisms that make organic carbon compounds from carbon dioxide , but get energy by oxidizing inorganic substances such as hydrogen sulfide, ammonia, or ferrous ions.
      • C. Photoheterotrophs—use light for energy but must obtain their carbon in organic form. Some marine prokaryotes use this mode of nutrition.
      • D. Chemoheterotrophs—must consume organic molecules for both energy and carbon . This mode of nutrition is found widely among prokaryotes as well as protists, fungi, and animals .
    • III. Oxygen requirements
      • A. Some prokaryotes cannot grow in the absence of oxygen for cellular respiration and are called obligate aerobes .
      • B. Some prokaryotes are poisoned by oxygen and are called obligate anaerobes . These prokaryotes normally convert energy by fermentation .
      • C. Some prokaryotes are flexible and are called faculative anaerobes and use oxygen if it is present, but can grow by fermentation in an anaerobic environment.
    • IV. Ecological role of Prokaryotes
      • A. Chemical recycling—primary decomposers of dead plant and animal bodies and waste products and thereby recycling matter.
    • B. Involved in symbiotic relationships
        • Mutualism +/+
        • Commensalism +/neutral
        • Parasitism +/-
    • C. Agents of disease
      • Tuberculosis is caused by Mycobacterium tuberculosis
      • Lyme disease is caused by a spirochette bacterium called Borrelia burgdorferi
      • 2. Usually cause illness by producing poisons called endotoxins
      • Example— Cholera is called by a bacterial exotoxin that causes the human gut to release chloride ions in to the gut and water follows by osmosis