Biology Exam1 chapter 5

Biology Exam1 chapter 5 - Chapter 5: Biological Membranes...

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Chapter 5: Biological Membranes Pg. 107: The Structure of Biological Membranes Plasma membrane: surrounds cells and physically separates it from the outside world; also regulates passage of materials in and out of the cell Phospholipids form bilayers in water o Phospholipid: contains two fatty acid chains linked to two of the three carbons of a glycerol molecule Fatty acids make up the hydrophobic part of phospholipid Negatively charged phosphate group linked to the third carbon is hydrophilic o Amphipathic molecules: molecules which have distinct hydrophilic and phobic regions o Have cylindrical shape which helps associate with water o Detergent: amphipathic molecules with single hydrocarbon chain (circle) Current data support a fluid mosaic model of membrane structure o Fluid mosaic model: a cell membrane consists of a fluid bilayer of phospholipid molecules in which the proteins are embedded or otherwise associated Biological membranes are two-dimensional fluids o A single phospholipid molecule can travel laterally across the surface of a eukaryotic cell in seconds Too fluid: membrane is weakened Too rigid: transport of certain substances are inhibited (low temperatures) o Some organisms compensate for temperature changes by altering the fatty acid content If cold: high proportions of unsaturated fatty acids o Some membrane lipids stabilize membrane fluidity within certain limits Ex: cholesterol At low temp: act as “spacers” between hydrocarbon chains restricting van der Waals forces that would solidify the membrane Biological membrane fuse and form closed vesicles o Do not form free ends o Flexible, allowing cell membranes to change shape without breaking o May fuse with other bilayers with proper conditions Membrane proteins include integral and peripheral proteins o Integral proteins: firmly bound to the membrane; can only release them by disrupting bilayer with detergents; amphipathic Transmembrane proteins: extend completely through the membrane Only once or wind back through many more times Alpha helix with hydrophobic amino acid side chains projecting out from the helix into hydrophobic region o Peripheral proteins: not embedded in the lipid bilayer; located on inner or outer surface of plasma membrane, bound to exposed regions of integral proteins by noncovalent interactions; easily removable Proteins are oriented asymmetrically across the bilayer o Proteins for inner membrane are manufactured by free ribosomes to move to membrane through cytoplasm o Proteins for outer membrane are manufactured like protein destined to be exported from the cell Sugar added to protein in ER lumen -> glycoprotein transported to Golgi
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Biology Exam1 chapter 5 - Chapter 5: Biological Membranes...

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