Cell Membranes
CELL MEMBRANES........................................................................................................................................ 1
FUNCTIONS OF PLASMA MEMBRANE..........................................................................................................................2
FLUID MOSAIC MODEL............................................................................................................................................2
MEMBRANE LIPIDS....................................................................................................................................... 2
Phospholipids:.................................................................................................................................................2
Glycolipids: part of sphingolipid family...........................................................................................................4
Cholesterol:.....................................................................................................................................................5
ASYMMETRY AND HETEROGENEITY OF MEMBRANE BILAYER...........................................................................................5
Transverse asymmetry:...................................................................................................................................5
Lateral heterogeneity:....................................................................................................................................5
MEMBRANE LIPID MOVEMENT................................................................................................................................5
Lipid-translocator Proteins (embedded in bilayer).........................................................................................5
Mechanism of translocation ‘flip and flop’................................................................................................................6
LIPID RAFTS:......................................................................................................................................................... 6
MEMBRANE PROTEINS.................................................................................................................................. 6
INTEGRAL MEMBRANE PROTEINS..............................................................................................................................6
– helices:.........................................................................................................................................................7
Hydropathy (Hydrophobicity) Plots:...............................................................................................................7
Glycophorin – glycoproteins on Red blood cells.............................................................................................7
Glucose transporter:.......................................................................................................................................7
- sheets:...........................................................................................................................................................8
Porins:.............................................................................................................................................................8
Advantages of B-strands over a-helices:.........................................................................................................8
PERIPHERAL PROTEINS............................................................................................................................................8
LIPID-LINKED MEMBRANE PROTEINS.........................................................................................................................8
1. N-Myristoylation:........................................................................................................................................9
2. S-Palmitoylation:.........................................................................................................................................9
3. Prenylated anchors.....................................................................................................................................9
Lipid-anchored proteins as ‘Switching devices’..............................................................................................9
MEMBRANE TRANSPORT.............................................................................................................................. 9
1. PASSIVE DIFFUSION..........................................................................................................................................10
2. FACILITATED DIFFUSION.....................................................................................................................................10
Using channel proteins: “gate”.....................................................................................................................10
Using carrier proteins: conformational change............................................................................................10
3. PRIMARY ACTIVE TRANSPORT.............................................................................................................................10
Sodium/Potassium Pump..............................................................................................................................10
4. SECONDARY ACTIVE TRANSPORT (CO-ACTIVE TRANSPORT)........................................................................................11
ELECTROCHEMICAL GRADIENTS:..............................................................................................................................11
Concentration gradient:................................................................................................................................11
Electric Gradients..........................................................................................................................................12
1
, Cell Membranes
Functions of plasma membrane
1. Physical barrier, structural support & protection
2. Transport – selective permeability
3. Organelle (ER, Golgi, Lysosomes) delineation and individuality
4. Cell recognition – intercellular communication – signal transduction.
Fluid mosaic model
- Membrane Bilayer is made up of mosaic of lipids, proteins and carbs.
- Not a rigid or static structure; fluid-like
o Constituents that make up membrane are capable of movement, giving the
dynamic, fluid-like consistency.
- Bilayer:
o 2 layers opposite each other. Each layer = leaflet
o Range from 5 to 10nm thick (depending on cell type)
o Lipids, proteins and carbs form structure of layer but proportions of each vary
depending on cell type.
Membrane Lipids
Phospholipids, glycolipids, cholesterol
Phospholipids:
- Basic structure:
o Backbone molecule
o 1 or 2 fatty acid chains (Hydrophobic)
o Phosphate group
o May or may not have alcohol containing group.
o That are amphipathic molecules
2
CELL MEMBRANES........................................................................................................................................ 1
FUNCTIONS OF PLASMA MEMBRANE..........................................................................................................................2
FLUID MOSAIC MODEL............................................................................................................................................2
MEMBRANE LIPIDS....................................................................................................................................... 2
Phospholipids:.................................................................................................................................................2
Glycolipids: part of sphingolipid family...........................................................................................................4
Cholesterol:.....................................................................................................................................................5
ASYMMETRY AND HETEROGENEITY OF MEMBRANE BILAYER...........................................................................................5
Transverse asymmetry:...................................................................................................................................5
Lateral heterogeneity:....................................................................................................................................5
MEMBRANE LIPID MOVEMENT................................................................................................................................5
Lipid-translocator Proteins (embedded in bilayer).........................................................................................5
Mechanism of translocation ‘flip and flop’................................................................................................................6
LIPID RAFTS:......................................................................................................................................................... 6
MEMBRANE PROTEINS.................................................................................................................................. 6
INTEGRAL MEMBRANE PROTEINS..............................................................................................................................6
– helices:.........................................................................................................................................................7
Hydropathy (Hydrophobicity) Plots:...............................................................................................................7
Glycophorin – glycoproteins on Red blood cells.............................................................................................7
Glucose transporter:.......................................................................................................................................7
- sheets:...........................................................................................................................................................8
Porins:.............................................................................................................................................................8
Advantages of B-strands over a-helices:.........................................................................................................8
PERIPHERAL PROTEINS............................................................................................................................................8
LIPID-LINKED MEMBRANE PROTEINS.........................................................................................................................8
1. N-Myristoylation:........................................................................................................................................9
2. S-Palmitoylation:.........................................................................................................................................9
3. Prenylated anchors.....................................................................................................................................9
Lipid-anchored proteins as ‘Switching devices’..............................................................................................9
MEMBRANE TRANSPORT.............................................................................................................................. 9
1. PASSIVE DIFFUSION..........................................................................................................................................10
2. FACILITATED DIFFUSION.....................................................................................................................................10
Using channel proteins: “gate”.....................................................................................................................10
Using carrier proteins: conformational change............................................................................................10
3. PRIMARY ACTIVE TRANSPORT.............................................................................................................................10
Sodium/Potassium Pump..............................................................................................................................10
4. SECONDARY ACTIVE TRANSPORT (CO-ACTIVE TRANSPORT)........................................................................................11
ELECTROCHEMICAL GRADIENTS:..............................................................................................................................11
Concentration gradient:................................................................................................................................11
Electric Gradients..........................................................................................................................................12
1
, Cell Membranes
Functions of plasma membrane
1. Physical barrier, structural support & protection
2. Transport – selective permeability
3. Organelle (ER, Golgi, Lysosomes) delineation and individuality
4. Cell recognition – intercellular communication – signal transduction.
Fluid mosaic model
- Membrane Bilayer is made up of mosaic of lipids, proteins and carbs.
- Not a rigid or static structure; fluid-like
o Constituents that make up membrane are capable of movement, giving the
dynamic, fluid-like consistency.
- Bilayer:
o 2 layers opposite each other. Each layer = leaflet
o Range from 5 to 10nm thick (depending on cell type)
o Lipids, proteins and carbs form structure of layer but proportions of each vary
depending on cell type.
Membrane Lipids
Phospholipids, glycolipids, cholesterol
Phospholipids:
- Basic structure:
o Backbone molecule
o 1 or 2 fatty acid chains (Hydrophobic)
o Phosphate group
o May or may not have alcohol containing group.
o That are amphipathic molecules
2
