AP Biology
CHAPTER 7: MEMBRANE
STRUCTURE AND FUNCTION
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 proteins
 Carrier 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/cha
pter2/animation__how_the_sodium_potassiu
m_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