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Biological Membranes. 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

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biological membranes1
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
types of membrane lipids
Types of Membrane Lipids
  • Glycerophospholipids
  • Sphingolipids
  • Cholesterol
properties of lipid aggregates

Properties of Lipid Aggregates

Micelles, Liposomes, and Bilayers

Driving Force = Hydrophobic Effect

cylindrical lipids
Cylindrical Lipids

Individual lipids are cylindrical

-cross-section of head = tail

properties uses of liposomes

Properties/Uses of Liposomes

Single Bilayer

(inner and outer leaflets)

Delivery of Therapeutic Agents

Stable — purification

Manipulate internal content

Delivery — fusion with plasma membrane

bilayer formation by phospholipids
Bilayer Formation by Phospholipids

Aqueous phase

Aqueous phase

transition temperature more rigid more fluid
Transition Temperature=more Rigid; =more fluid
  • Increases with chain length
    • Tm = more rigid
  • Increases with degree of saturation
    • More saturated = more rigid
  • Cholesterol decreases membrane fluidity
lateral diffusion
Lateral Diffusion

Figure 9-16b

permeability of lipid bilayer
Permeability of Lipid Bilayer

Semi-permeable

Hydrophilic molecules

Non-permeable

Facilitated diffusion

Active transport

Hydrophobic molecules

Permeable

Simple diffusion

membrane carbohydrates
Membrane Carbohydrates
  • Mostly oligosaccharides
  • Variety of sugars
  • Glycolipids
  • Glycoproteins

Glycoprotein

membrane proteins

Membrane Proteins

Peripheral or Extrinsic Proteins

Integral or Intrinsic Proteins

peripheral or extrinsic proteins
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
integral or intrinsic proteins
Integral or Intrinsic Proteins
  • Not easily dissociated or solubilized
    • Detergents
    • Chaotropic agents — disrupt water structure
  • Retain associated lipid
  • >average hydrophobic amino acds
  • Significant number hydrophilic amino acds
  • Asymmetrically oriented amphiphiles
  • Trans-membrane proteins
integral membrane proteins

Single transmembrane domain

Integral Membrane proteins

Multple transmembrane domains

Lipid Linked

composition of biological membranes protein lipid ratios
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
transmembrane proteins

Transmembrane Proteins

May contain -Helices

(and -Sheets)

functions of membrane proteins
Functions of Membrane Proteins
  • Catalysis of chemical reactions
  • Transport of nutrients and waste products
  • Signaling
reaction of tnbs with membrane surface phosphatidylethanolamine
Reaction of TNBS with Membrane Surface Phosphatidylethanolamine

Figure 9-33

redistribution of membrane lipids
Redistribution of Membrane Lipids
  • Flipases
  • Phospholipid Translocases(ATP-dependent active transport)
exposure of phosphatidylserine

Exposure of Phosphatidylserine

Blood clotting (tissue damage)

Removal from circulation (erythrocytes)

membrane subdomains
Membrane Subdomains
  • Basolateral Cells
    • Two sided cells
  • Microdomains
    • Concentration of specific lipids with specific proteins
      • Cardiolipin and the electron transport chain
  • Lipid Rafts
lipid rafts specific microdomain
Lipid RaftsSpecific Microdomain
  • Glycosphingolipids
  • Cholesterol
  • GPI-linked proteins
  • Transmembrane signaling proteins
  • Caveolae — e.g. internalization of receptor-bound ligands