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BIOLOGY CH-27 (ECOLOGICAL INTERACTIONS (STRUCTURAL AND FUNCTIONAL…

- - - - In eukaryotes that have cell walls, such as plants and fungi, the walls are usually made of cellulose.
      - Most bacterial cell walls contain peptidoglycan, a polymer composed of modified sugars cross-linked by short polypeptides.
      - The cell walls of prokaryotes differ in structure from those of eukaryotes.
      - The cell wall of many prokaryotes is surrounded by a sticky layer or polysaccharide or protein.
      - A key feature of nearly all prokaryotic cells is the cell wall, which maintains cell shape, protects the cell and prevents its form bursting in a hypotonic environment.
      - The walls of gram-negative bacteria have less peptidoglycan and are structurally more complex, with an outer membrane that contains lipopolysaccharides.
      - MOTILITY
        
        Of the various structures that enable prokaryotes to move, the most common are flagella.
        
        Flagella (flagellum) may be scattered over the entire surface of the cell concentrated at one or both ends.
        
        Half of prokaryotes are capable of taxis, a directed movement toward or away from a stimulus.
        
        The flagella of prokaryotes and eukaryotes also differ their molecular composition and their mechanism of propulsion.
- - - - By binary fission, a single prokaryotic cell divides into 2 cells, which then divide into 4,8 ,16, an so on.
      - Many prokaryotes can divide each 1-3 hours; some species can produce a new generation in only 20 minutes.
      - Many prokaryotes can reproduce quickly in favorable environments.
      - At this time one single prokaryotic cell could give rise to a colony outweighing Earth in only two days.
      - Prokaryotic populations can consist of many trillions of individuals---far more than populations of multicellular eukaryotes, such as plants or animals.
      - BACTERIA
        
        Every major mode of nutrition and metabolism is represented among bacteria, and even an small taxonomic group of bacteria may contain species exhibiting many different nutritional modes.
        
        There are some froups of bacteria.
        
        Bacteria include the vast majority of prokaryotic species familiar to most people from the pathogenic species that cause strep throat and tuberculosis to the beneficial species used to make swiss cheese and yogurt.
        
        Examples of the major groups of bacteria
        
        Proteobacteria
        
        Alpha Proteobacteria
        
        Beta Protebacteria
        
        Gamma Proteobacteria
        
        Delta Proteobacteria
        
        Epsilon Proteobacteria
        
        Chlamydias
        
        Spirochetes
        
        Cyanobacteria
        
        Gram-Positive Bacteria
- - - - In eukaryotes, the sexual processes of meiosis and fertilization combine DNA from two individuals in a single zygote.
      - Meiosis and fertilization do not occur in prokaryotes.
      - New mutations are a major source of variation in prokaryotic populations, additional diversity arises from genetic recombination, the combining of DNA from two sources.
      - Three mechanisms--transformation, transduction, and conjugation--can bring together prokaryotic DNA from different individuals (that is different cells).
      - Horizontal gene transfer is the movement of genes from one organism to another.
      - TRANSFORMATION AND TRANSDUCTION
        
        Transformation occurs when non pathogenic cells takes up a piece of DNA carrying the allele for pathogenicity and replaces its own allele with the foreign allele, an exchange of homologous DNA segments.
        
        Once inside the cell, the foreign DNA can be incorporated into the genome by homologous DNA exchange.
        
        Transformation; the genotype and possibly genotype of a prokaryotic cell are altered by the uptake of foreign DNA from its surroundings.
        
        Transducer result from accidents that occur during the phage replicative cycle.
        
        ARCHAEA
        
        Archaea live in environments so extreme that few other organisms can survive there.
        
        Archaea have many unique characteristics, as we would expect in a taxon that has followed a separate evolutionary path fro so long.
        
        Some archaea live in hot, cold or even some in moderate environments.
        
        Extremophiles, meaning "lovers" of extreme conditions, and include extreme halophiles and extreme thermphiles.
        
        Decomposers breaking down dead organisms as well as waste products and thereby unlocking supplies of carbon, nitrogen, and other elements.
- - - - Mutation in a different gene may alter the intracellular target protein for an antibiotic molecule, reducing its inhibitory effect.
      - Bacteria have "resistance genes," which code for enzymes that specifically destroy or otherwise hinder the effectiveness of certain antibiotics, such as tetracycline or ampicillin.
      - During the 1950's in Japan, physicians started noticing that some hospital patients with bacterial dysentery, which produces severe diarrhea, did not respond to antibiotics that had been effective in the past.
      - Resistance genes are often carried by plasmids known as R plasmids.
      - THE ROLE OF OXYGEN AND METABOLISM
        
        Obligate anaerobes, on the other hand, are poisoned by O2.
        
        Some obligate anaerobes live exclusively by fermentation; others extract chemical energy by anaerobic respiration.
        
        Obligate aerobes must use O2 for cellular respiration and cannot grow without it.
        
        Facultative anaerobes use O2 if it present but can also carry fermentation or anaerobic respiration in an anaerobic environment.
        
        METABOLIC COOPERATION
        
        Metabolic cooperation between different prokaryotic species often occurs in surface-coating colonies to grow.
        
        Cells produce polysaccharides and proteins that stick the cells to the substrate and to one another; these polysaccharides and proteins from the capsule, or slime layer.
        
        Cooperation between prokaryotic cells allows them to use environmental resources they could not use as individual cells.
        
        Biofilms are common in nature, but they can cause problems by contaminating industrial products and medical equipment and contributing to tooth decay and more serious health problems.