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Fluid Mosaic Model:
States that membranes are composed of a lipid bilayer containing various proteins and glycoproteins some of which are mobile while others are stationary
Fluid Mosaic Model:
Fluid? molecules are continuously removed and replaced with newly made molecules Can stretch Can reseal itself
Fluid Mosaic Model:
Composed of? 1. Lipids 2. Proteins 3. Carbohydrates (glycoproteins, glycolipids)
Fluid Mosaic Model:
Lipids?? Phospholipids more specifically Composed of:
Compounds with nitrogen Phosphate group Glycerol Saturated and unsaturated fatty acid chains
Fluidity of Membranes: membranes are not static hydrophobic and hydrophilic
interactions proteins and lipids can drift,
laterally in the membrane temperature does play a role on
membrane fluidity, permeability, enzyme activity
cholesterol fluidity and function
Roles of Membrane
1.Containment and Separation 2. Material Exchange 3. Information Detection 4. Identification 5. Attachment reinforcement 6. Movement and Metabolism
Membrane Proteins and their Functions:
Proteins determine most of the membranes specific functions
Bound to cytoskeleton on cytoplasmic side and ECM on extracellular side
Integral Proteins:
penetrate the hydrophobic core of the lipid bilayer
consists of one or more stretches of nonpolar amino acids
hydrophilic parts are exposed on either end of the bilayer
Peripheral Proteins:
not embedded in the membrane
loosely bound to the surface of the membrane
often bound to exposed parts of integral proteins
Functions of Membrane Proteins:
1. Transport 2. Enzyme activity 3. Cell to cell recognitions 4. Signal transduction 5. Intercellular joining 6. Attachment (cytoskeleton and
ECM)
The Permeability of the lipid bilayer:
Hydrophobic molecules(hydrocarbons), CO2, O2 Dissolve in the membrane and pass with
ease polar, hydrophilic molecules such as
ions Have trouble passing through the
membrane because of the hydrophobic core Glucose, water(polar molecules)
Pass slowly through the membrane
The Permeability of the lipid bilayer:
Transport Proteins Enhance the permeability of
membrane Substance specific Span the width of the membrane Two types:
Channel proteinsCarrier proteins
The Permeability of the lipid bilayer:
channel proteins: having a hydrophilic channel certain molecules and ions use to pass
through the membrane carrier proteins:
transmit molecules through the membrane by changing shape
Passive Transport:
Diffusion the tendency for molecules of a
substance to spread out evenly into the available space
Osmosis: diffusion of water across a semi-
permeable membrane
Passive Transport:
Facilitated Diffusion passive diffusion of polar molecules
and ions with the help of transport proteins
gated channels: need a stimulus to open((electrical or chemical stimulus)
Energy driven transport:
Active Transport: using energy to move a substance
against a concentration gradient uses carrier proteins energy is supplied by ATP See sodium/ potassium pump
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html
Bulk Transport
Passing through membrane by molecules too large to fit through proteins.
Relies on ability of membrane to change shape and create vesicles and reseal itself
Receptor-mediated Endocytosis Allows smaller molecules to enter
Molecules bind to specific receptor proteins
Egg cells take in yolk protein by this method
Cells transport substances across their membranes. Choose ONE of the following four types of cellular transport. Osmosis Active Transport Facilitated Diffusion Endocytosis/exocytosis
For the transport type you choose, Describe the transport process and explain how
the organization of cell membranes functions in the movement of specific molecules across membranes