Chapter 2 Notes

Chapter 2 Notes - Cytoplasmic Membrane(CM The cell membrane...

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Cytoplasmic Membrane (CM): - The cell membrane in bacterial and archael cells - composed of phospholipids and proteins Phospholipids: - amphipathic molecules - hydrophilic (phosphorus-containing) heads, hydrophobic (hydrocarbon) tails - form lipid bilayers 1 layer is called a leaflet Self-Assembly of Phospholipid Bilayer: - in water, phospholipids self assemble/arrange o arrange into spherical bilayered vesicle o caused by electronegativity, polarity, chemical bonds Insertion of proteins into Lipid Bilayer: - as protein is being made by ribosome, it’s “pushed” into bilayer by accessory proteins Electronegativity: - The tendency of an atom in a molecule to pull electrons towards itself - Differences in electronegativity cause polar covalent bonds - O has the highest electronegativity and H&P have the lowest O > N > S = C ~ H = P High ------------------- Low Polarity: - distribution of charge in individual bonds - used to characterize chemical groups (2-4 atoms) o Polar Covalent Bonds: polar molecule, polar group Membrane Assembly: - hydrophobic hydrocarbon tails become sandwiched between leaflets - hydrophilic heads remain exposed to aqueous environment outside cell ~ heads have high content of polar groups .: forms H-Bonds with water ~ heads are also attracted to non-polar groups of hydrocarbon tails (PDID) ** Hydrophilic heads remain pointing out because H-Bonds are stronger than PDID bonds ** Hydrophobic Effect: - positioning of hydrophobic tails between leaflets is the increase in entropy - by minimizing contact with water fewer hydrogen cages form around non-polar substance .: less constriction of water molecules .: increase in overall entropy Functions of the Cytoplasmic Membrane 1. Delineation of the Cytoplasm: -Surround aqueous compartment where most chemical reactions occur - Lipids with a single hydrocarbon tail are cone shaped o Hydrophobic Effect forces creation of ‘Micelle’ o Micelle’s don’t contain internal aqueous solution - Membrane phospholipids have 2 tails and are cylindrically shaped o Hydrophobic effect forces creation of a bilayered sheet o Sheet folds back on itself and forms a vesicle
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2. Creation of a selectively permeable barrier: - The difference between lipid and membrane bilayers is the presence of proteins in the membrane - Membrane proteins allow the membrane to act as a selectively permeable barrier o Vesicles aren’t very permeable o Allows the uptake of nutrients and loss of wastes products o Slows the loss of important cell parts and interference of pathogens How Molecules Cross the Membrane - Bilayers are fluid and are in constant thermal motion
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