BIOL 2410 Lecture Notes - Lecture 3: Lipid Raft, Lipid Bilayer, Fluid Mosaic Model
15 Nov 2016
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Lecture 3 – BIOL 2410
Cell Membranes and Transport
Cell Membranes
1. Structure of the cell membrane
a. Functions
b. Structure, fluid mosaic
c. Component molecules
i. Phospholipids
ii. Cholesterol
iii. Sphingolipids
iv. Proteins
2. Transport across the cell membrane
a. Diffusion/osmosis
b. Protein mediated transport
c. Vesicular transport
Cell Membrane - Function
Also called plasma membrane
Physical isolation
o Separates intra and extracellular compartments
Regulation of exchange with the environment
o Controls movement of solutes from inter and extra cellular, semipermeable
Communication between the cell and its environment
o Contains receptors that detect stimuli and begin a signal cascade in response
Structural support
o Membrane proteins bind to cytoskeleton, extracellular matrix and house junction proteins
Cell Membrane - Composition
Lipids - major component
o Phospholipids - 8nm in thickness
Head is phosphate and R
Tail is fatty acid and glycerol
o Sphingolipids
o Cholesterol - a steroid
Proteins
o Integral
Transmembrane
Lipid - anchored - only on one side
o Peripheral - one side of membrane - not attached to membrane but are attached to other
proteins
Carbohydrates - only on extracellular side - never on intracellular side
o Glycoproteins
o Glycolipids
o Glycohalix - all carbohydrates on extracellular side
Cytoskeleton - keeps structure - bound to membrane proteins
Fluid mosaic model of membrane structure
Cell Membrane - Phospholipids
find more resources at oneclass.com
find more resources at oneclass.com
Major component
Several different varieties
o R group
o Saturation
Polar head groups toward aqueous sides, non polar fatty acid tails inside
Membrane phospholipids form bilayers, micelles or liposomes
Bilayer forms a sheet
Micelles - droplets of phospholipids - lipid digestion
Liposomes - droplet - have an aqueous center - 2 layers of phospholipids
Used in drug delivery
Cell Membrane - Cholesterol
Flat molecule, hydrophobic, slips between fatty acid tails
Cholesterol regulates membrane fluidity
More cholesterol you have - the more fluid the membrane
Slows diffusion of molecules across membrane, makes it impermeable
Keeps membrane flexible over range of temperatures
Cell Membranes - Sphingolipids
Fatty acid tails, slightly longer than phospholipids, head may be phospholipid or glycolipid
Aggregate together to form lipid rafts - some with high density of cholesterol
Lipid rafts produce areas of specialization as some proteins bind here
Cell Membrane - Protein
Up to 50 different types in cell membranes - can be peripheral, integral, or transmembrane
Peripheral - attach non covalently to other membrane proteins - integral - or heads of
phospholipids, can be removed without disrupting membrane - ex. - enzymes, cytoskeleton
anchors
Integral - tightly bound, can only be removed with detergents that disrupt membrane
Lipid anchored proteins
Modified by the addition of a fatty acid
Often associate with lipid rafts - sphingolipids
May have strongly hydrophobic sections that allow it to associate with lipid bilayer
Transmembrane proteins
Span the lipid bilayer once or several times
Approx. 20-25 hydrophobic AA to span the membrane
Hydrophobic sites are in lipid bilayer
Hydrophilic sites exposed to aqueous environment
May have glycoproteins on extracellular side
May have phosphate from ATP on intracellular side
Protein:Lipid Ratio
Ratio and types of membrane components differ for each cell type
The more metabolically active a cell, the more protein it has in the membrane
Proteins increase permeability
Red blood cell - 49% protein - 43% lipid - 8% carbo.
Mycelin membrane around nerve cells - 18% Protein - 79% lipid - 3%carbo.
Inner mitochondrial membrane - 76% protein - 24% lipid - 0% carbo.
Other Players
Cytoskeleton
Interacts with membrane proteins
Flexible 3D skeleton of fibrous proteins throughout the cytoplasm
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Cell membranes: structure of the cell membrane, functions, structure, fluid mosaic, component molecules. Proteins: transport across the cell membrane, diffusion/osmosis, protein mediated transport, vesicular transport. Physical isolation: separates intra and extracellular compartments. Regulation of exchange with the environment: controls movement of solutes from inter and extra cellular, semipermeable. Communication between the cell and its environment: contains receptors that detect stimuli and begin a signal cascade in response. Structural support: membrane proteins bind to cytoskeleton, extracellular matrix and house junction proteins. Lipids - major component: phospholipids - 8nm in thickness. Tail is fatty acid and glycerol: sphingolipids, cholesterol - a steroid. Lipid - anchored - only on one side: peripheral - one side of membrane - not attached to membrane but are attached to other proteins. Carbohydrates - only on extracellular side - never on intracellular side: glycoproteins, glycolipids, glycohalix - all carbohydrates on extracellular side. Cytoskeleton - keeps structure - bound to membrane proteins.
