1. 4. The basics of lipids and membrane structure

2. 1. Introduction Introduction
Lipid molecule : hydrophobic (water-hating), non-polar hydrocarbon chains
: hydrophilic (water-loving), polar head groups
FIGURE 4.1 A cartoon of four representative lipid aggregate structures.

3. 1. Introduction Why membrane lipids form aggregates
FIGURE 4.2 Thylakoid membranes from a chloroplast illustrating the sharp bends (at the arrows) between the flat regions.
Why membrane lipids form aggregates
When the different structures are formed
How the physicochemical properties of the lipids are used by the cell

4. 2.1 lipid classes and their properties

5. 2.1 lipid classes and their properties
FIGURE 4.3 Representative structures for each lipid category.

6. 2.1 lipid classes and their properties
FIGURE 4.4 A dipalmitoylphospholipid molecule where the chiral carbon on the glycerol moiety is indicated.
FIGURE 4.5 Phosphatidylcholine with some of the most common fatty acyl chains.

7. 2.1 lipid classes and their properties
Phosphatidylcholine position

8. 2.1 lipid classes and their properties
2.1.1 Phospholipids
phosphocholine
Glycerophospholipid
Sphingophospholipid
spingosine
Fatty acid
FIGURE 4.6 Example of components constituting up a sphingomyelin lipid.
phosphatidylinositol

9. 2.2 Membrane lipids form liquid crystalline phases
FIGURE 4.8 Structures of some common liquid crystalline phases.

10. 2.2 Membrane lipids form liquid crystalline phases
Calorimetric: temperature-composition
X-ray scattering(SAXS)
spectroscopic
2.2.1 Gibbs phase rule and description of phase behavior
(Lamellar liquid crystalline)
* F+p=c+2
F+p=c+1
F: degrees of freedom
p: coexisting phases
c: components
2: temperature, pressure
(Gel)
dipalmitoylphosphatidylcholine
FIGURE 4.7 A partial phase diagram of DPPC and water.

11. 2.2 Membrane lipids form liquid crystalline phases
2.2.1 Gibbs phase rule and description of phase behavior
FIGURE 4.9 A partial phase diagram of the system monoglucosyldiacylglycerol (MGlcDAG)/heavy water, where MGlcDAG comes from the bacterium A. laidlawii.

12. 3.1 Lipid packing and spontaneous curvature
FIGURE As an example of a typical lipid, the figure shows a phospholipid .

13. 3.1 Lipid packing and spontaneous curvature
packing parameter
FIGURE A schematic drawing of the shape of a lipid molecule forming spherical micelles.
* P=v/al
FIGURE Lipid molecules of different shapes and packing parameters.
v: volume of the fluid hydrocarbon chains
l: length of the hydrophobic chain
a: optimal cross-sectional area of the polar head group

14. 3.1 Lipid packing and spontaneous curvature
FIGURE Left: The definition of the two radii of membrane curvature. Right: illustration of the definition of the sign of the radius of curvature (by conbention).

15. 3.1 Lipid packing and spontaneous curvature
Formation of HII phase
Curvature energy : Acyl chains must stretch to fill the hydrophobic regions
Packing energy
Hydrophobic region
FIGURE As the shape of the lipid molecules (enlarged) get less wedge-shaped, the radius of curvature of the cylinders building up the HII phase increases and the water (blue) uptake increases in the HII cylinders.

16. 3.1 Lipid packing and spontaneous curvature
bicontinuous cubic phases
sponge (L3) phase
FIGURE Schematic illustration of the structure of one of the bicontinuous cubic phases.
FIGURE A schematic picture of a sponge (L3) phase.

17. 3.1 Lipid packing and spontaneous cruvature
3.1.1 Lipid packing and lateral pressure ① ② ③
FIGURE Illustration of the lateral pressure, p(z), profile in a lipid bilayer.
FIGURE High lateral pressure, p(z), can result in a change in the conformation of an integral membrane protein (striped or dashed) as illustrated by the cross-section A(z).

18. 3.1 Lipid packing and spontaneous cruvature
3.1.1 Lipid packing and lateral pressure
FIGURE The structure of the closed state of the large membrane channel, MscL, in M. tuberculosum outer membrane viewed perpendicularly to the membrane surface.
FIGURE A schematic picture of the effect on the bilayer curvature (and therefore on the lateral pressure) and a mechanosensitive protein (MscL).
Microbiol. Mol. Biol.Rev. 2003

19. 4.1 Regulation of membrane lipid composition
Acyl chain structure
Polar head group structure
Reshuffling of the acyl chains to form new lipid species
4.1.1 Escherichia coli
FIGURE The bacterium E. coli grows in a “window.”

20. 4.1 Regulation of membrane lipid composition
4.1.2 Acholeplasma laidlawii: 아코이에플라스마 라이들라위이
FIGURE Structure of the gluco- and phospholipids in the A. laidlawii membrane: 1. MGlcDAG; 2. MAMGlcDAG; 3. DGlcDAG; 4. MADGlcDAG; 5. GPDGlcDAG; 6. MABGPDGlcDAG.

21. 4.1 Regulation of membrane lipid composition
4.1.2 Acholeplasma laidlawii 아코이에플라스마 라이들라위이
FIGURE The bacterium A. laidlawii grows when its lipids are in a lamellar state.
FIGURE Acyl chain unsaturation as a function of the chain length in the membrane of surviving A. laidlawii bacteria.

22. 4.2 Role of nonlamellar-forming lipids in membrane function
4.2.1 Special membrane structures
Nonlamellar-forming lipids  nonbilayer
or bilayer structure with a small radius of curvature
Nonlamellar structure  fusion ,fission (융합 분열)
4.2.2 Influence on the activity of membrane-associated proteins
Efficiency of protein incorporation
 lipids forming nonbilayer structures
 molecules known to destabilize the bilayer structure

23. 4.3 Membrane fusion
Membrane fusion: membrane trafficking, vesicle-mediated transport, sperm-egg fusion, virus-cell fusion
FIGURE Above. Steps in the fusion of membrane.

24. Vesicle docking using ER-to-Golgi transport in yeast
The vesicle docking is specified by tethering complex
restricted to TRAPP location

25. 4.4 Lipid synthesizing enzymes
FIGURE A cartoon showing how the cell can regulate membrane elastic stress upon binding of CCT (green) to a DOPE (left) in comparison to a DOPC (right) bilayer.
Phosphocholine cytidylycerol

26. 4.5 Lipid domains and rafts in membranes
fluid mosaic model
FIGURE A cartoon of the fluid mosaic model of a biological membrane from 1972 according to Singer and Nicolson.
FIGURE Above: Cholesterol induces lateral phase separation into domains in the membrane containing glycerophospho- and sphingolipids.

27. 4.5 Lipid domains and rafts in membranes
FIGURE Generic temperature/concentration phase diagram of a system with a saturated phospholipid, cholesterol (CHOL) and water.

28. 4.5 Lipid domains and rafts in membranes
Caveolae : lipid raft subtype
: caveolin – scaffold protein
FIGURE Picture of the flask-like invaginations called caveola in the plasma membrane.