PNB 2264 Chapter Notes - Chapter 3: Fluid Mosaic Model, Tight Junction, Lipid Bilayer

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Section 3.2 - Membrane
Membranes most universal function is to act as a selective barrier to the passage
of molecules
Allows some molecules to cross while excluding others
Plasma membrane
regulates the passage of substances into and out of the cell
Detect chemical messengers arriving at the cell surface
Link adjacent cells together by membrane junctions
Anchor cells to the extracellular matrix
Membranes surrounding cell organelles
allow the selective movement of substances between the organelles and
the cytosol
Membrane Structure
Structure determines function
Phospholipids - major membrane lipid
One end is charged (polar) and the one end, which is two long fatty acid
chains, is nonpolar
Amphipathic
Polar = surfaces of the membrane (attraction to the polar water molecules
in the extracellular fluid and cytosol)
Cholesterol and phospholipids have a coordinated function in maintaining an
intermediate membrane fluidity
Two classes of membrane proteins
Integral
Closely associated with the membrane lipids and cannot be
extracted from the membrane without disrupting the lipid bilayer
amphipathic , having polar amino acid side chains in one region of
the molecule and nonpolar side chains clustered together in a
separate region
Can form channels which ions or water can cross the membrane
Or can be associated with the transmission of chemical signals
across the membrane
Peripheral
Not amphipathic and do not associate with the nonpolar regions of
the lipids in the interior of the membrane
Located on the membrane surface where they are bound to the
polar regions of the integral membrane proteins
Fluid mosaic model - mix of membrane proteins are free to move in a sea of
lipid
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Document Summary

Membranes most universal function is to act as a selective barrier to the passage of molecules. Allows some molecules to cross while excluding others. Regulates the passage of substances into and out of the cell. Detect chemical messengers arriving at the cell surface. Link adjacent cells together by membrane junctions. Allow the selective movement of substances between the organelles and the cytosol. One end is charged (polar) and the one end, which is two long fatty acid chains, is nonpolar. Polar = surfaces of the membrane (attraction to the polar water molecules in the extracellular fluid and cytosol) Cholesterol and phospholipids have a coordinated function in maintaining an intermediate membrane fluidity. Closely associated with the membrane lipids and cannot be extracted from the membrane without disrupting the lipid bilayer. Amphipathic , having polar amino acid side chains in one region of the molecule and nonpolar side chains clustered together in a separate region.

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