BIO 1140 Lecture Notes - Lecture 6: Glycolipid, Glycerol, Ion Channel

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BIO1140 B Dr. Caroline Petit-Turcotte
Membranes 01.26.2017
Functions:
Form a barrier with selective permeability allows certain things in or out
Organize and scaffold; allow compartments inside the cell
Regulate solute transport
Receive signals with receptor proteins
Communication between cells
Types of Membrane
All of them have phospholipids that form bilayer of cell and organelle membrane; determines whether or
not a molecule can go through and how they can get through (protein channel, transport protein)
Types of membranes differ in lipid and protein content, types of lipids and proteins, and glycolipids and
glycoproteins
o Cell with a cell wall have thicker membrane with peptidoglycan layer
o Myelin sheath from Shawwn cells that wrap their membrane around an axon
Fluid Mosaic Model
Fluid lipid molecules with embedded, free-floating or anchored proteins to allow things through
Arranged in sheets, non-covalently bound; two facing sheets/ fluid lipid layers provide structure
Mosaic of different proteins that have various functions (specificity)
Fluidity within each layer, the lipids continuously change place; rarely change from one layer to the other (flip-
flop; requires energy and enzyme) i.e lateral diffusion occurs very quickly
the membrane is asymmetric; both layers have different compositions b/c the environments inside and
outside the cell are different
o Outside composition allowing the membrane to:
be selective about what gets in and out
for cell-to-cell communication (i.e dead cell and macrophages)
protection and prevent certain things from entering or attaching the cell
cellular recognition for other cells to recognize what kind of cell it is (glycoproteins
Composition of the Lipid Layers
phospholipids are the most abundant lipids in the membrane bilayer
o 1 polar head (has a charge), 2 hydrocarbon tails (nonpolar, not charged); amphipathic
(hydrophilic and hydrophobic area)
hydrocarbon tails can vary in length (14-24 carbon atoms); one tail usually has one or
more cis-double bonds (unsaturated) and the other does not (saturated); affect how
tightly the molecules pack against one another affecting fluidity of membrane
presence of unsaturated doule od produes kik, affet how tightly the oleules
pack against one another affecting fluidity of membrane
o 4 main phosphatidylethanolamine, phosphatidylserine (-), phosphatidylcholine, sphingomyelin
o allow small and uncharged particles through the membrane by diffusion i.e CO2 and O2
o its shape and amphipathic nature of the lipid molecules cause them to form bilayers
spontaneously in aqueous evironments
glycolipids (glycosphingolipids) are 1 or 2 fatty acid chains with single or multiple sugar groups attached
via glycerol or sphingosine
o important for cellular recognition and signaling, antigens (i.e blood groups); found on outer layer
sterols are 4-ring hydrocarbons; only in eukaryotes; important in fluidity in terms of arrangement and in
relation to temperature (buffers)
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