3 BIO 326R cell structure 1

3 BIO 326R cell structure 1 - BIO 326R Cell Structure...

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BIO 326R Cell Structure
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Eukaryotes vs. Prokaryotes Eukaryotes DNA in a Nucleus – membrane bound Splice RNA Polyadenylated mRNA Poly A stabilizes mRNA, translational efficiency Mitochondria or chloroplasts Cell wall Animals – none Plants – cellulose Fungi – chitin Prokaryotes DNA in a region called nucleoid Very rarely splice Polyadenylated RNA Poly A is degradation signal No mitchondria, chromatophores instead of chloroplasts Cell wall (peptidoglycan) Some exceptions (Mycoplasma)
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Lipid Bilayers ~8nm thick Hydrophobic Hydrophilic phosphate “head” groups (-) (-) (-) (-) (-) (-) (-) (-) (-) (-) (-) (-)
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Cytoplasmic membrane functions Protective barrier Generally speaking, the cell membrane will exclude molecules that are large or hydrophilic Nutrients Specific proteins within the membrane will import nutrients. The membrane will prevent their escape Signal Transduction Chemotaxis – cell must ‘sense’ its envrionment Metabolism Electron transport, chemiosmosis Secretion Toxins, siderophores
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Fluid Mosaic Model The phospholipid bilayer exists as a planar fluid Phospholipids can rotate about their axis Phospholipids can migrate within the membrane They cannot (easily) “flip flop” to switch sides The membrane is flexible. Without support from cytoskeletons and/or cell walls it is easily deformable If the temperature is lowered too much, the Van der Waals interactions within the hydrophobic region may become strong enough for the membrane to no longer be fluid – i.e. it solidifies and most movement within the membrane ceases. X Rotation and lateral diffusion are allowed
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Gram Negative Cytoplasmic membrane Porin: allows passage of molecules < 700 daltons Peptidoglycan Lipoprotein Periplasmic space Outer membrane Lipopolysaccharide (LPS) OUT IN (cytoplasm)
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Gram positive  Teichoic Acid, Lipoteichoic acid Periplasmic space Peptidoglycan Phospholipid bilayer Cell wall OUT IN (cytoplasm)
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Cell Wall Function In an isotonic solution, a bacterial cell can live without its cell wall This can be demonstrated by growing the bacteria in the presence of penicillin Due to the penicillin, no new peptidoglycan can be synthesized The cell will lose whatever shape the cell wall provided and “round up” into a spherical shape (called a protoplast), but can remain viable as long as the solution is isotonic
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3 BIO 326R cell structure 1 - BIO 326R Cell Structure...

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