BIOL1004 Lecture Notes - Lecture 6: Phosphatidylcholine, Cell Membrane, Lipid Bilayer
BIOL1004: Topic 1 – Biochemistry
Lecture 6 – Plasma Membrane
• The plasma membrane is the boundary that separates the interior of the living cell from its
nonliving surroundings
• The ells plasa erae ehiits seletie pereailit, alloig soe substances to cross
it more easily than others
• Eukaryotic cells contain internal membrane-bound compartments, the internal composition of
which differs from that of the cell cytosol.
• Biologial eraes are fluid osais of lipids ad proteis.
•
Fatty Acids
• Fatty acids are a component of membrane lipids
• Butter - stearic acid
o Saturated
• Olive oil - Oleic acid
o Cis double bond causes bending
o Poly-unsaturated fats are more fluid than saturated, due to the kinks that the double
bonding in unsaturated fats cause. They can't pack close together
• Hydrophobic, non-polar end
• Hydrophilic, polar (acid) end
• Membrane lipids are formed form fatty acids linked to glycerol
o
Phospholipids
• Phospholipids are the most abundant lipid in biological membranes.
• Phospholipids are amphipathic molecules, containing hydrophobic and hydrophilic regions.
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• The hydrophobic region is comprised of fatty acid tails.
• The hydrophilic region is comprised of the glycerol, a covalently linked phosphate group, and
an additional charged group (e.g. choline, a small positively charged molecule).
• Phosphatidyl choline
o
• Phospholipid bilayer
o Phospholipids spontaneously form bilayers
o Minimised exposure of the hydrophobic "tails" to water molecules, while at the same
time maximising exposure of the hydrophilic head groups to the water molecules.
o Movement of phospholipids
•
• These are not held together by any kind of covalent bonds, just polar attraction
Membranes
• Membrane fluidity
o As temperatures cool, membranes switch from a fluid state to a solid state.
o The temperature at which a membrane solidifies depends on the types of lipids.
o Membranes rich in unsaturated fatty acids are more fluid that those rich in saturated
fatty acids.
o Membranes must be fluid to work properly; they are usually about as fluid as olive oil.
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