Lecture 2.1 Notes

Lecture 2.1 Notes - Cell Morphology and the importance of...

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2/1/10 Cell Morphology and the importance of being small Major bacterial cell morphologies Coccus Rod Spirillum Spirochete Budding and appendaged bacteria Filamentous bacteria •Representative morphologies – many variations are known •Even square and star shaped organisms have been characterized •Continuum of morphologies w/ some very common and others more unusual The big thing about being small •Transport rates are a function of the surface area of the cell membrane relative to cell volume. •Rapid nutrient and waste transport into and out of the cell, allowing for faster metabolic rates and growth rates. •Rapid growth rates rapid production of large populations of cells, which rapidly adapt to changing conditions and greatly affect the constitution of an ecosystem As cells get larger, the surface-area-to-volume ratio decreases. Surface area increases with the square of the radius and volume increases with the cube. Nevertheless, there is still enormous variation in the size of prokaryotic organisms (Table 4.1) but they are typically much smaller than eukaryotic organisms Cytoplasmic Membrane: Structure Permeability Barrier The cytoploasmic membrane allows cells to sequester nutrients and provides a barrier to unwanted substances Transport of molecules Energy conservation Proton motive force (pmf) The properties of cytoplasmic membranes Relatively permeable to small hydrophobic molecules Less permeable to small uncharged polar molecules Very much less permeable to large uncharged polar molecules Essentially impermeable to charged molecules and ions Differences in membrane structure among different types of organisms A major difference in chemical composition of membranes of eucaryotes and procaryotes is that eucaryotic membranes contain sterols (e.g. cholesterol) and the membranes of procaryotes do not. Sterols increase the rigidity of membranes and can make up 5-25% of total lipids in eucaryotes.
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Membranes of the Bacteria contain hopanoids, which appear to serve a similar function. Hopanoids not found in the membranes of species from Archea. Lipids of Archaea differ from those of other organisms but overall architecture of membrane is similar. Hydrophobic side chains of the membranes of the
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Lecture 2.1 Notes - Cell Morphology and the importance of...

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