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Biological Membranes

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Title: Biological Membranes Author: Chemistry UCLA Last modified by: Heather Created Date: 10/17/2009 10:15:39 PM Document presentation format: On-screen Show (4:3) – PowerPoint PPT presentation

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Title: Biological Membranes


1
Biological Membranes
2
Biological Membranes
  • Organized assemblies of lipids, proteins and
    small amounts of carbohydrates
  • Regulate composition of intracellular medium by
    controlling flow of nutrients, waste products,
    ions, etc. in and out of cell
  • Scaffolding
  • Oxidative phosphorylation
  • Photosynthesis
  • Nerve impulses
  • Hormone receptors

3
(No Transcript)
4
Types of Membrane Lipids
  • Glycerophospholipids
  • Sphingolipids
  • Cholesterol

5
Membrane Glycerophospholipids
6
Sphingolipids(Sphingomyelin)
7
Cholesterol
8
Amphiphilicity
9
Properties of Lipid Aggregates
  • Micelles, Liposomes, and Bilayers
  • Driving Force Hydrophobic Effect

10
Van der Waals Envelope(Fatty Acids)
Figure 9-13a
11
Micelle(single-tailed lipids)
12
Cylindrical Lipids
Individual lipids are cylindrical -cross-section
of head tail
13
Liposomes
14
Electron Micrograph of Liposome
Figure 9-15
15
Properties/Uses of Liposomes
  • Single Bilayer
  • (inner and outer leaflets)
  • Delivery of Therapeutic Agents
  • Stable purification
  • Manipulate internal content
  • Delivery fusion with plasma membrane

16
Bilayer Formation by Phospholipids
Aqueous phase
Aqueous phase
17
Membrane composition
18
Phase Transition in a Lipid Bilayer(Transition
Temperature)
Figure 9-18
19
Transition Temperaturemore Rigid more fluid
  • Increases with chain length
  • Tm more rigid
  • Increases with degree of saturation
  • More saturated more rigid
  • Cholesterol decreases membrane fluidity

20
Membrane composition
21
Which membrane composition is more rigid?
A B
Average Chain length 16.0 17.0
Ratio UnsaturatedSaturated Fatty acids 2.0 0.5
22
Asymmetry within Membranes
23
Lipid Diffusion in Membranes
24
Transverse Diffusion
Figure 9-16a
25
Flippase/Floppase/Scramblase
26
Lateral Diffusion
Figure 9-16b
27
Permeability of Lipid Bilayer
Semi-permeable Hydrophilic molecules Non-permeabl
e Facilitated diffusion Active
transport Hydrophobic molecules Permeable Simple
diffusion
28
Membrane Carbohydrates
  • Mostly oligosaccharides
  • Variety of sugars
  • Glycolipids
  • Glycoproteins

Glycoprotein
29
Membrane Proteins
  • Peripheral or Extrinsic Proteins
  • Integral or Intrinsic Proteins

30
Peripheral or Extrinsic Proteins
  • Easily dissociated
  • High ionic strength
  • pH changes
  • Free of attached lipid
  • Water-soluble
  • (e.g. cytochrome c)
  • Normal amino acid composition

31
Integral or Intrinsic Proteins
  • Not easily dissociated or solubilized
  • Detergents
  • Chaotropic agents disrupt water structure
  • Retain associated lipid
  • gtaverage hydrophobic amino acds
  • Significant number hydrophilic amino acds
  • Asymmetrically oriented amphiphiles
  • Trans-membrane proteins

32
Integral Membrane proteins
Single transmembrane domain
Multple transmembrane domains
Lipid Linked
33
Lipid Linked Proteins
34
Prenylated Proteins
Page 268
35
Prenylated Proteins
Page 268
36
Glycosylphosphatidylinositol (GPI) Linked Proteins
37
Core Structure of the GPI Anchors of Proteins
Figure 9-24
38
Composition of Biological Membranes(protein-lipid
ratios)
  • Myelin 0.23
  • Eukaryotic plasma membrane 1.0
  • (50 protein and 50 lipid)
  • Mitochondrial inner membrane 3.2

39
Asymmetric Orientation
40
Detecting Asymmetric Orientation of Membrane
Proteins
  • Surface Labeling
  • Proteases

41
Transmembrane Proteins
  • May contain ?-Helices
  • (and ?-Sheets)

42
Human Erythrocyte Glycophorin A
Figure 9-20
43
Identification of Glycophorin As Transmembrane
Domain
Figure 9-21
44
Structure of Bacteriorhodopsin
Figure 9-22
45
X-Ray Structure of E. coli OmpF Porin
Figure 9-23a
46
X-Ray Structure of E. coli OmpF Porin Trimer
Figure 9-23b
47
Functions of Membrane Proteins
  • Catalysis of chemical reactions
  • Transport of nutrients and waste products
  • Signaling

48
Hydrophillic compounds need help
49
Glucose transporter
50
Plasma Membrane StructureFluid Mosaic Model
Figure 9-25
51
Evidence for Mobility of Membrane Proteins
52
Fusion of Mouse and Human Cells
Figure 9-26 part 1
53
Mixing of Human and Mouse Membrane Proteins
Figure 9-26 part 2
54
Fluoresence Recovery after Photobleaching (FRAP)
Technique
Figure 9-27a
55
Fluoresence Recovery after Photobleaching (FRAP)
Results
Figure 9-27b
56
Distribution of Membrane Phospholipids
57
Distribution of Membrane Phospholipids in Human
Erythrocyte Membrane
Figure 9-32
58
Reaction of TNBS with Membrane Surface
Phosphatidylethanolamine
Figure 9-33
59
Location of Lipid Synthesis in a Bacterial
Membrane
Figure 9-34
60
Redistribution of Membrane Lipids
  • Flipases
  • Phospholipid Translocases(ATP-dependent active
    transport)

61
Distribution of Membrane Phospholipids in Human
Erythrocyte Membrane
Figure 9-32
62
Exposure of Phosphatidylserine
  • Blood clotting (tissue damage)
  • Removal from circulation (erythrocytes)

63
Membrane Subdomains
  • Basolateral Cells
  • Two sided cells
  • Microdomains
  • Concentration of specific lipids with specific
    proteins
  • Cardiolipin and the electron transport chain
  • Lipid Rafts

64
Basolateral CellsAsymmetric cell
65
Lipid RaftsSpecific Microdomain
  • Glycosphingolipids
  • Cholesterol
  • GPI-linked proteins
  • Transmembrane signaling proteins
  • Caveolae e.g. internalization of receptor-bound
    ligands

66
Lipid rafts
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