Chapt. 11, Membrane Structure - SUNY Geneseolewisj/Cell.04/Lectures/Chapt11_3.pdfChapt. 11, Membrane...
Transcript of Chapt. 11, Membrane Structure - SUNY Geneseolewisj/Cell.04/Lectures/Chapt11_3.pdfChapt. 11, Membrane...
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Chapt. 11, Membrane Structure
• Functions of cell membrane
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Chapt. 11, Membrane Structure
• Functions of cell membrane– As a container/ barrier to movement of
small molecules. Figure 1-1
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• Functions of cell membrane, cont.– Import and export of molecules.– Information transducer.– Movement. Figure 1-2.
Chapt. 11, Membrane Structure
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• The lipid bilayer is composed (in animals) ofphospholipids, cholesterol and glycolipids.
• All are amphipathic.
• Structure of lipids results in self-assemblyinto a bilayer.
Chapt. 11, Membrane Structure, Lipids
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• Phospholipid structure.
Chapt. 11, Membrane Structure, Lipids
Fig 11.6
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• Phospholipid structure.– Phospholipids make up the bulk of the membrane
bilayer.– The four major components of a phospholipid.– Hydrophobic and hydrophilic components of a
phospholipid.– There are several types of organic headgroups.– There is usually one or more double bonds in one
of the fatty tails.
Chapt. 11, Membrane Structure, Lipids
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• Phospholipids self-assemble into a 2dimensional lipid bilayer.– The importance of the hydrophobic interactions
Chapt. 11, Membrane Structure, Lipids
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– Review of the hydrophobic interaction. Panel 2-2Chapt. 11, Membrane Structure, Lipids
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– Review of the hydrophobic interaction. (Fig 11-9modified)
Chapt. 11, Membrane Structure, Lipids
20 high-energy watermolecules
13 high-energy watermolecules
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• Phospholipids self-assemble into a 2dimensional lipid bilayer.– Review of the hydrophobic interaction.– The importance of van der Waals forces.
Chapt. 11, Membrane Structure, Lipids
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• Phospholipids self-assemble into a 2dimensional lipid bilayer.– Review of the hydrophobic interaction. Fig 11-9– The importance of van der Waals forces.– Result: Open or closed membrane sheets (Figs.
11-12, 11-13, 11-14)
Chapt. 11, Membrane Structure, Lipids
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Figs. 11-12, 11-13
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Figs. 11-12, 11-14
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• Lipid bilayers are said to be fluid.– What do we mean by “fluid”?– The potential types of phospholipid mobility. Fig
11-15.
Chapt. 11, Membrane Structure, Lipids
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• Membrane phospholipid structure and degreeof fluidity.– What is “freezing” or “crystallization”?– Effect of temperature on fluidity.– Effect on length of hydrocarbon tails on fluidity.– Effect of unsaturation on fluidity.
Chapt. 11, Membrane Structure, Lipids
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• Structure of Cholesterol. Fig 11-7b, 11-16.
Chapt. 11, Membrane Structure, Lipids
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• The effect of cholesterol on membranefluidity. (Fig. 11-16)
Chapt. 11, Membrane Structure, Lipids
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• Glycolipid structure. Fig 11-7c
Chapt. 11, Membrane Structure, Lipids
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• Terminology.– “Leaflet”
Chapt. 11, Membrane Structure, Lipids
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• Terminology.– “Leaflet”– Problems with
“inside” and “outside”– Suggested
terminology“cytosolic” and “non-cytosolic”
Chapt. 11, Membrane Structure, Lipids
Fig. 11-19
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• The bilayer is asymmetrical.– Phospholipids - some phospholipids are mainly in
the cytosolic leaflet, others in the non-cytosolicone. Fig. 11-17
Chapt. 11, Membrane Structure, Lipids
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• The bilayer is asymmetrical.– Glycolipids - found (almost) exclusively on the
non-cytosolic leaflet. Fig. 11-17
Chapt. 11, Membrane Structure, Lipids
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• The bilayer is asymmetrical..– Cholesterol -- found on both leaflets as it easily
flips.
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• Amounts of proteins in membranes.• Some functions of proteins. (Table 11-1)
Chapt. 11, Membrane Structure, Proteins
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• Types of membrane proteins; transmembraneFig 11-21
Chapt. 11, Membrane Structure, Proteins
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• Types of membrane proteins; lipid linked Fig11-21.
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• Types of membrane proteins; peripheral(protein attached) Fig 11-21.
Chapt. 11, Membrane Structure, Proteins
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• A more detailed consideration oftransmembrane proteins.– Proteins that have buried hydrophobic parts go
all the way through the bilayer; there are nohalf-transmembrane proteins.
– The portion of the protein that is in thehydrophobic interior always adopts into a alphahelix or beta sheet. Why? (Fig. 11-24 and Fig10-15 in Big Alberts.)
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Fig. 11-24 and Fig 10-15 in Big Alberts.
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• Difficulties in studying membrane proteins.– Hard to physically separate protein of interest
from other proteins.– Even if you could, hydrophobic portions of the
proteins would aggregate.
• The solution: detergents. Fig 11-26, 11-27
Chapt. 11, Membrane Structure, Proteins
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Fig. 11-26
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Fig 11-26
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• You can isolate proteins, Now what?– Sequence.– Use to raise antibodies (Panel 4-6).– SDS gel electrophoresis (Panel 4-5).
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SDS PAGE (preparing the sample)
SDS
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SDS PAGE (loading the gel)
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SDS PAGE (after 2 hrs.)
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SDS PAGE (after 2 hrs.)
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112,000 daltons90,000 daltons
66,000 daltons
34,000 daltons
15,000 daltons
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• Membrane proteins are polar andasymmetric.
Chapt. 11, Membrane Structure, Proteins
NH2
COOH
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• How do we know membrane proteins are polarand asymmetric?
• Vectorial labeling– Reagent cannot penetrate membranes– Reagent can label proteins.
Chapt. 11, Membrane Structure, Proteins
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Vectorial labeling
SDS gel
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Vectorial labeling
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Vectorial labeling
SDS gelstained for total protein
SDS gelvectoriallabel
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• The complete structure is known forrelatively few proteins.– Difficulties in determining structure.– Examples of membrane proteins where the
structure is known.• Bacteriorhodopsin (Fig. 11-28).
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Fig. 11-28 Bacteriorhodopsin
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• The complete structure is known forrelatively few proteins.– Difficulties in determining structure.– Examples of membrane proteins where the
structure is known.• Bacteriorhodopsin (Fig. 11-28).• Photosynthetic reaction center of Rhodopseudomonas.
(Fig. 11-29)
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Fig. 11-29
Bacterialphoto-chemicalreactioncenter
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• The red blood cell and the plasma membrane.– Why study the R !BC?– Kinds of proteins present
• A multipass membrane protein (band 3)• A single pass membrane protein (glycophorin)• Numerous peripheral proteins including:
– Spectrin– Actin
• A summary Fig 11-31.
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Fig. 11-32
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• How common are RBC proteins?
• RBC proteins and related proteins in humanhealth.– Spherocytosis– Muscular Dystrophy
Chapt. 11, Membrane Structure, Proteins
http://www.diseasedir.org.uk/genetic/genex01.htm
Dystrophin
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• Glycoproteins as well as glycolipids havesugars on the non-cytosolic side.– Especially true for plasma membranes (where
they are present on the outside of the cell), butalso on luminal side (=inside = non-cytosolic side)of internal compartments.
– Fig 11-32
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Fig. 11-32
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• Possible functions of sugars on the plasmamembrane.– Membrane protection and lubrication– Electrical insulation– Cell recognition
• An example: snagging neutrophils to infection sites.Fig. 11-33
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55Fazlebas & Kim, 2003, Science 299:355-356
• Another example: the embryo makes selectins that snag carbohydrates on the uterine wall.
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• Many proteins can diffuse within the lipidbilayer.– Why does this make sense?– What kind of mobility is possible?
• No flip-flop.• Rapid spinning• Lateral diffusion
Chapt. 11, Protein mobility
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• How can one show lateral mobility? Fig 11-34
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• Fluorescence Recovery after Photobleaching(FRAP): a way to measure rates of lateraldiffusion.
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• Restrictions of lateral mobility. (Fig. 11-35)
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• An example where this is very important:tight junctions in the intestinal epithelium.(Fig. 11-36)
Chapt. 11, Protein mobility