10 LC Concepts in Molecular Biology 20.10.2022
Transport and structure of membranes
➢ Amphiphilic lipids spontaneously form micelles and bilayers
The major classes of the lipids are amphiphilic, having a hydrophobic part
(typically a fatty acid, saturated or not) and a hydrophilic cater group.
o Glycerophospholipid → they glicerin is acilated in sn1 and
sn2 position; the sn3 position gets phosphorylated and could
carry and additional head group. The acil chains on the other
hand are hidrophobic
o Sphingosine → a primary alcohol
o Free fatty acid
As amphiphilic lipids natural partition into high order structures, their
structure depends on their shape.
➢ How do we know lipids form a bilayer?
o Gorder and Grendel
With a langmour trough, a small bath filled with the acquose solution, some lipids are
injected forming a monomolecular layer. They can be pushed to measure the total area that
the monomolecular layer.
They did this with, in particular with erythrocytes (which don’t have any further internal
membrane), taking its lipids and measuring the area occupied. It was found out that the
area occupied by all the lipids was almost always twice as large as the surface of the
erythrocytes.
They came out the first model of the lipid bilayer, similar to the one nowadays.
Davison and danielli proposed an other model where basically surface was covered by proteins on the
other sides of the bilayer.
Singer and Nicholson proposed the lipid mosaic model.
, 10 LC Concepts in Molecular Biology 20.10.2022
➢ Membrane dimensions
The head groups are separated by roughly 3.5 to 4.0 nm nanometers apart, and the membranes have
different thickness depending on which membrane is.
➢ Properties of the bilayer
o Viscosity → 100 – 250 mPaxs(=cP)
water’s viscosity is one, olive oil 15-50 cP centipoise
o Elastic Moduli
it means how much energy you need in order to expand the material or compress it.
Membranes can easisly be bend, but they cannot be stretched or compressed easily.
o Lateral diffusion → 1 micro m2/s
o Spontaneous flipping → 10^-5/s (t1/2 circa 20hrs)
o Electrical resistance → 10^8 Ohm/cm2
It is quite amazing, allowing the transfer of electric signal
o Permeability → polar, charged particles ions are impermeable.
➢ How many lipids are there in the cells?
there are a few thousand different lipids in the cells, there are quite diverse and this is quite hard to
study.
LIPID’S DIVERSITY
- GPL glycerophospholipids
They have the glycerol as a backbone, which is esterified by a fatty acid at sn1 and sn2 position. Sn1
is typically there is a saturated fatty acid and sn2 non saturated fatty acids. The ester linkage
between the glycerol and the fatty acid, a phosphor group at sn3 position and some head group
that can be quite different.
- Sphingolipid
There is a sphingosine base, the N-acyl chain, which is a primer amin-alcohol, the headgrop again
can be very different and depending on the base, it could be asphingonine, asphingosine, and
betahidrocy…
f. ex. sphingomiolyn of neurons.
Transport and structure of membranes
➢ Amphiphilic lipids spontaneously form micelles and bilayers
The major classes of the lipids are amphiphilic, having a hydrophobic part
(typically a fatty acid, saturated or not) and a hydrophilic cater group.
o Glycerophospholipid → they glicerin is acilated in sn1 and
sn2 position; the sn3 position gets phosphorylated and could
carry and additional head group. The acil chains on the other
hand are hidrophobic
o Sphingosine → a primary alcohol
o Free fatty acid
As amphiphilic lipids natural partition into high order structures, their
structure depends on their shape.
➢ How do we know lipids form a bilayer?
o Gorder and Grendel
With a langmour trough, a small bath filled with the acquose solution, some lipids are
injected forming a monomolecular layer. They can be pushed to measure the total area that
the monomolecular layer.
They did this with, in particular with erythrocytes (which don’t have any further internal
membrane), taking its lipids and measuring the area occupied. It was found out that the
area occupied by all the lipids was almost always twice as large as the surface of the
erythrocytes.
They came out the first model of the lipid bilayer, similar to the one nowadays.
Davison and danielli proposed an other model where basically surface was covered by proteins on the
other sides of the bilayer.
Singer and Nicholson proposed the lipid mosaic model.
, 10 LC Concepts in Molecular Biology 20.10.2022
➢ Membrane dimensions
The head groups are separated by roughly 3.5 to 4.0 nm nanometers apart, and the membranes have
different thickness depending on which membrane is.
➢ Properties of the bilayer
o Viscosity → 100 – 250 mPaxs(=cP)
water’s viscosity is one, olive oil 15-50 cP centipoise
o Elastic Moduli
it means how much energy you need in order to expand the material or compress it.
Membranes can easisly be bend, but they cannot be stretched or compressed easily.
o Lateral diffusion → 1 micro m2/s
o Spontaneous flipping → 10^-5/s (t1/2 circa 20hrs)
o Electrical resistance → 10^8 Ohm/cm2
It is quite amazing, allowing the transfer of electric signal
o Permeability → polar, charged particles ions are impermeable.
➢ How many lipids are there in the cells?
there are a few thousand different lipids in the cells, there are quite diverse and this is quite hard to
study.
LIPID’S DIVERSITY
- GPL glycerophospholipids
They have the glycerol as a backbone, which is esterified by a fatty acid at sn1 and sn2 position. Sn1
is typically there is a saturated fatty acid and sn2 non saturated fatty acids. The ester linkage
between the glycerol and the fatty acid, a phosphor group at sn3 position and some head group
that can be quite different.
- Sphingolipid
There is a sphingosine base, the N-acyl chain, which is a primer amin-alcohol, the headgrop again
can be very different and depending on the base, it could be asphingonine, asphingosine, and
betahidrocy…
f. ex. sphingomiolyn of neurons.
