BIO 011 Lecture Notes - Lecture 6: Lipid Bilayer, Phospholipid, Osmotic Pressure
Chapter 6 – Membranes
Jadzia Wray
Membranes are permeability barriers
- Inside of cell has a
certain pH and structure.
- Membrane keeps good
stuff in and bad stuff out
Membranes are made of phospholipids.
- They are made of phospholipid bilayers.
- Interactions among the tails helps hold
the membrane together. Polar heads are
outward and nonpolar tails are inward.
What kind of chemistry drives formation of membrane bilayers in this particular configuration?
- The chemistry of water drives this formation
- If we tried to assemble these molecules in oil, the polar head groups would try to run away from
the nonpolar oil and they would stay on the inside while the tails would be on the outside.
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Phospholipids can move within the plane of the membrane.
- Rotation: tails can just move around against each
other
- Lateral diffusion: the phospholipids can move
around through the plane of the bilayer, just
moves down the line.
- Flip-flop: does’t eally ee happe, oleule
ould’t e ale to stik its head though the
nonpolar tail area to move down to the other
side
o Enzymes (biological catalysts) would be
able to give a biological input and the
molecule would be able to flip around
- Flexion: bending of the tails
Membranes come in different flavors.
- Lipid composition of membranes vary.
- Phospholipids vary in fatty acid chain length, degree of saturation, and phosphate groups →
changes the orientation, and properties.
- How might this variability be biologically relevant?
o More double bonds = more kinky = change properties of membrane
Animal cell membranes may be up to 25% cholesterol,
which is important for membrane integrity.
Cholesterol makes membranes firm
- Cholesterol and long-chain,
saturated fatty acids pack tightly,
making a less-fluid membrane.
- As temperature decreases,
movement of molecules and
cellular processes slow.
o If you increased heat, van
der waals forces break.
Put cholesterol in and it
fills the gap and puts
some rigidity back into the cell
- Some organisms change the lipid content of the cell membranes when they get cold.
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Membranes are more than just lipids
- Membranes also contain proteins; the number varies depending on membrane function.
- Transporter molecule provides the channel for the hydrophilic molecule to get inside. The circles
and triangles are things let through the cell.
- Anchors (blue things are proteins) stay anchored in the lumen and it holds on to the yellow thing.
Intermediate filament is the brown thing.
- Receptors communicate things into the cell, so the reaction can actually happen. The protein can
detect signals, or
presence of molecules,
and communicate
imbalances into the
cell.
- Enzymes: converting
X to Y is done by
enzymes. They are
biological catalysts.
- Integral membrane
proteins span the
phospholipid bilayer.
- Peripheral membrane
proteins lack exposed
hydrophobic groups and do
not penetrate the bilayer.
- (A) Single transmembrane proteins, multi transmembrane proteins, and betta sheet
transmembrane proteins (form a barrel and let things travel through)
- (B) Monolayer associated: can span the membrane
- (C.) Lipid linked proteins. Pik suiggles ae hydoao tails, does’t go though all the ay,
just itegates ight though it ad that’s it.
- (D) protein attached – function depends on the type
Membrane Proteins
- Some membrane proteins can move freely within the bilayer, while some are anchored to a
specific region.
- When cells are fused experimentally, some proteins from each cell distribute themselves
uniformly around the membrane.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Inside of cell has a certain ph and structure. Membrane keeps good stuff in and bad stuff out. Interactions among the tails helps hold the membrane together. Polar heads are outward and nonpolar tails are inward. If we tried to assemble these molecules in oil, the polar head groups would try to run away from the nonpolar oil and they would stay on the inside while the tails would be on the outside. Phospholipids can move within the plane of the membrane. Rotation: tails can just move around against each other. Lateral diffusion: the phospholipids can move around through the plane of the bilayer, just moves down the line. Phospholipids vary in fatty acid chain length, degree of saturation, and phosphate groups changes the orientation, and properties. How might this variability be biologically relevant: more double bonds = more kinky = change properties of membrane. Animal cell membranes may be up to 25% cholesterol, which is important for membrane integrity.
