BIOL 2311 Lecture Notes - Lecture 5: Micelle, Pinocytosis, Passive Transport
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CH 5: membranes and transport
Structure of phospholipids:
-bilayer is stable because water’s affinity for hydrogen bonding never stops
Structure consists of
-Glycerol – a 3-carbon polyalcohol
–2 fatty acids attached to the glycerol
-Nonpolar and hydrophobic (“waterfearing”)
–Phosphate group attached to the glycerol
-Polar and hydrophilic (“water-loving”)
Spontaneously forms a bilayer
– Fatty acids are on the inside
– Phosphate groups are on both surfaces
Liposomes are also phospholipid bilayers but folded.
Fluid mosaic membrane:
The fluid mosaic model describes the plasma membrane structure as a mosaic of phospholipids,
cholesterol, proteins, and carbohydrates.
Membrane Structure Cellular membranes have four components:
1. phospholipid bilayer
2. transmembrane proteins = integral membrane proteins: integrated completely into the membrane
structure with their hydrophobic membrane-spanning regions interacting with the hydrophobic region
of the phospholipid bilayer.
3. interior protein network
4. cell surface markers
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Properties of Membrane bilayers :
-Phospholipids spontaneously form micelles or bilayers when placed in water
-Phospholipid bilayer is fluid - proteins and the lipids move around within the bilayer
-What affects membrane fluidity?
Composition of the membrane saturated bonds vs. unsaturated bonds protein movement in the
membranes (figure 5.4)
-ex: mouse and human membrane protein fusion
Chose protein from human cell, which bonded to an antibody- hybrid. only possible if proteins are
moving around in the membrane bilayer.
Saturated: stacking, membrane is less fluid
Unsaturated: membrane is more fluid
Double bonds-there are kinks
Structure of Membrane Proteins:
Proteins can be anchored to lipids in the bilayer
Pores
Transmembrane proteins
– single-pass anchors
– multiple-pass channels and carriers
Lipid-anchored membrane proteins
- anchored to a phospholipid in one layer of the membrane
- possess nonpolar regions that are inserted in the lipid bilayer
- are free to move about in their environment
-protein anchored to phospholipid
Transmembrane/integral membrane proteins:
- alternating hydrophobic and hydrophilic proteins
-span the lipid bilayer (transmembrane proteins)
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Document Summary
Bilayer is stable because water"s affinity for hydrogen bonding never stops. The fluid mosaic model describes the plasma membrane structure as a mosaic of phospholipids, cholesterol, proteins, and carbohydrates. Phospholipids spontaneously form micelles or bilayers when placed in water. Phospholipid bilayer is fluid - proteins and the lipids move around within the bilayer. Composition of the membrane saturated bonds vs. unsaturated bonds protein movement in the membranes (figure 5. 4) Chose protein from human cell, which bonded to an antibody- hybrid. only possible if proteins are moving around in the membrane bilayer. Proteins can be anchored to lipids in the bilayer. Anchored to a phospholipid in one layer of the membrane. Possess nonpolar regions that are inserted in the lipid bilayer. Are free to move about in their environment. Possess at least one transmembrane domain - nonpolar (hydrophobic) regions of the protein are embedded in the interior of the bilayer.