AP Biology

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:

Mosaic? proteins embedded in or

attached to a phospholipid bilayer

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

Fluid Mosaic Model: Amphiphathic molecule:

Fluid Mosaic Model:

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

Membrane Proteins and their Functions:

Two major types of membrane proteins: Integral peripheral

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

Endocytosis

Take large molecules in

Cell membrane pinches in and surrounds molecule in membrane

Phagocytosis

“Cell eating”: engulfing entire cell; done by some white blood cells

Receptor-mediated Endocytosis Allows smaller molecules to enter

Molecules bind to specific receptor proteins

Egg cells take in yolk protein by this method

Pinocytosis

“Cell drinking”; cells take in fluid and the solutes it contains

Exocytosis

Expelling large molecules; reverse of endocytosis

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