BIOL 112 Lecture Notes - Lecture 7: Lipid Bilayer, Brownian Motion, Passive Transport
15 Jun 2018
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BIOL 112: MEMBRANES
Proteins can be amphipathic;
- Polar and charged amino acids are hydrophilic (Thr)
- Non-polar AA are hydrophobic (Val) → needs this stretch
- Amphipathic proteins can integrate lipid bilayers ( helix (secondary structure bonds H
bonds in the plane of the helix) the side groups point out of the sides
o Needs a string of 10 AA to cross through the lipid bilayer, proteins inserted do
not move up/down inside the lipid bilayer but sideways
Fluid Mosaic: membrane proteins inserted in the protein
- Unique function of proteins; integral (transmembrane → inside), peripheral (interacts
with the integral membrane → outside)
Membrane Proteins: mounds and pits are in the middle of the lipid bilayer
- Why does’t reak soewhere else istead of the leaflets of the bilayer?
- The easiest way to break it is through H bonds, they are locked and stable however
between the 2 leaflets is VDW interactions which are too weak
Functions of Membranes: Barrier Transport
A) Planar bilayers: Artificial membranes
o Phospholipids, soap bubbles,
o Membranes are selectively permeable: (e.g. gases can freely move because they
are non-polar, water/glycerol which are polar/small that can cross through a
certain degree, glucose/sucrose oth large/polar they a’t go through eause
they a’t ross hydrophoi iterior)
Passive Transport:
Diffusion – NET transport along a concentration gradient (mixing result), happens until it
reaches equilibrium (still move but net movement = 0)
- Determined by distance, temperature (higher → molecules move more rapidly), size of
molecule and steepness of concentration gradient (-
Reason: rado walk
(Brownian Motion) of
Individual molecules due to
thermal regulation*
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BIOL 112 Full Course Notes
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Document Summary
Polar and charged amino acids are hydrophilic (thr) Non-polar aa are hydrophobic (val) needs this stretch. Fluid mosaic: membrane proteins inserted in the protein. Unique function of proteins; integral (transmembrane inside), peripheral (interacts with the integral membrane outside) Membrane proteins: mounds and pits are in the middle of the lipid bilayer. The easiest way to break it is through h bonds, they are locked and stable however between the 2 leaflets is vdw interactions which are too weak. Diffusion net transport along a concentration gradient (mixing result), happens until it reaches equilibrium (still move but net movement = 0) Determined by distance, temperature (higher molecules move more rapidly), size of molecule and steepness of concentration gradient (- ) Osmosis: diffusion of water across a selectively permeable membrane. Water flows along the concentration gradient to the solution side. Moves from regions of high water concentration to low water concentration. Dissolve something in water, less molecules in the solution side.
