AP BIOLOGY

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AP BIOLOGY CELL STRUCTURE FUNCTION
CELL MEMBRANES 2008 Dr. Michael C. Potter Paul
VI Catholic High School
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CELL MEMBRANES
The cell membrane is the interface between the
internal and the external environment of the
cell. Cell membranes encase ALL living cells Cell
membranes are two molecules thick (10 nm)
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• Structure of Cell Membrane
• A. Bilayer Lipid Membrane
• 1. Amphipathic (Polar)
• a. hydrophilic head (outside)
• b. hydrophobic head (inside)

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2. Type of Phospholipid determine permeability
a. Double bond vs. Single bond b. Long
tail vs. Short tail B. Proteins Multiple
Function/Structure
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C. Cholesterol 1. Fluidity Buffer a.
Increase viscosity at high temp b. Decrease
viscosity at low temp 2. Strengthens Membrane
a. Fills gaps between tails of lipids with
double bonds
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D. Temperature Effect 1. High Temp-low
viscosity high permeability 2. Low
Temp-high viscosity low permeability E.
Models of Membranes 1. Davson-Danielli Model
(1935) 2. Fluid Mosaic Model (1972)
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Proteoglycans
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II. Components of Cell Membranes A. Lipid
Bilayer B. Membrane Proteins 1. Integral
Membrane Proteins a. Three Domains Cytosoli
c Face Exoplasmic Face Membrane Spanning
Domain
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B. Membrane Proteins 1. Integral Membrane
Proteins b. Allow Movement Thru Membrane
c. Anchor Membranes d. Act as
Receptors e. Function as Enzymes f.
Signal Transduction g. Cell-Cell
Recognition
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B. Membrane Proteins 1. Integral
Membrane Proteins h. Types 1.
Transmembrane Proteins 2. Membrane
Associated Proteins 3. Lipid-Linked
Proteins 4. Protein Attached
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Ex. Of Glycocalyx
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B. MEMBRANE PROTEINS Transmembrane Proteins
a. Single Pass (Glycophorin in RBC) b.
Multipass Channels, Pores, Gates ß-Barrel P
orin Proteins
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MEMBRANE PORE PROTEIN
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B. MEMBRANE PROTEINS Membrane Associated
Proteins Exoplasmic Face Anchors Recept
ors Signaling Proteins Attachment
Proteins Recognition Proteins
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CELL RECOGNITION (IDENT.) PROTEIN
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B. MEMBRANE PROTEINS Membrane Associated
Proteins Cytosolic Face Attachment
Proteins (Spectrin-RBCs) Anchors Structu
ral Proteins Signaling Proteins
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Types of Cell-Cell Junctions
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III. CELL JUNCTIONS A. OCCLUDING JUNCTIONS
Seal cells so tightly together to prevent even
a small molecule from leaking across Seen
in vertebrates Also called Tight
Junctions Example occludin, claudins
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Tight Junction Structure
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Tight Junctions
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III. CELL JUNCTIONS B. ANCHORING JUNCTIONS
Mechanically attaches cell to its neighbors
.e.g. Desmosomes cell rivets attach to
intermediate filament Adherens Attach to
actin fibers Cadherins
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Desmosome Structure
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Desmosome
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Adherens junctions
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III. CELL JUNCTIONS B. ANCHORING JUNCTIONS
Focal Adhesions Hemidesmosomes Bind cells
to extracellular matrix (integrin proteins)
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Integrins, Focal Adhesions Hemidesmsomes
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• PRINCIPAL PROTEINS OF ECM
• Collagen
• 2. Fibronectin
• 3. Elastin
• 4. Laminins
• 5. Vitronectin
• 6. Proteoglycans
• 7. Hyaluronon
• 8. Heparan Sulfate

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Structure of Collagen
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Structure function of elastin protein
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Extracellular Matrix
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III. CELL JUNCTIONS C. COMMUNICATING
JUNCTIONS Mediate the passage of chemical
or electrical signals from cell-cell a
direct cytoplasmic link. 1. Gap Junctions
(animals) 2. Plasmodesmata (plants) 3.
Synapses (nerve cells)
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GAP JUNCTION STRUCTURE
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Communicating Junction
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Communicating Junction
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PLASMODESMATA
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PLASMODESMATA
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MOVEMENT THROUGH MEMBRANES

• STRUCTURE OF MEMBRANE
• 1. Bilayer Phospholipid
• 2. Integrated Membrane Proteins
• 3. Permeability of Membrane
• a. Nonpolar molecules
• b. Macromolecules
• c. Ions

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MOVEMENT THROUGH MEMBRANES
B. PASSIVE PROCESSES
1. Diffusion Kinetic Molecular Theory
Diffusion Gradient Dynamic Equilibrium
Energy Consideration Potential v. Kinetic
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MOVEMENT THROUGH MEMBRANES
B. PASSIVE PROCESSES (contd) 2.
Osmosis Movement of water Follows
Concentration Gradient Determined by ALL
solutes Osmotic Pressure
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OSMOSIS
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OSMOSIS
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MOVEMENT THROUGH MEMBRANES
B. PASSIVE PROCESSES (contd) Types of
Solutions Isotonic Isosmotic Hypertonic H
ypotonic Turgor Pressure
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MOVEMENT THROUGH MEMBRANES
C. COTRANSPORT SYSTEMS Requires Carriers
and Channels Systems from Passive to
Active Transporters consist
of Uniporters Symporters Antiporters (2o
active transport)
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MOVEMENT THROUGH MEMBRANES
D. ACTIVE PROCESSES 1. Bulk
Passage Phagocytosis Pinocytosis Exocytosis
2. Receptor Mediated Endocytosis 3.
Active Transport
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Phagocytosis
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PINOCYTOSIS
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MOVEMENT THROUGH MEMBRANES 2. Receptor
Mediated Endocytosis Highly Specific Clathrin
Coated Pits More efficient than
pinocytosis Important in cholesterol levels
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MOVEMENT THROUGH MEMBRANES 3. Active
Transport Uses 33 resting cell
energy Operates AGAINST gradient Must function
continuously Different systems for different
ions Selective Protein Carrier Molecules
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Gas Transport in The RBC
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Tight Junctions
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BASAL LAMINA Structure Lamina lucida Lamina
densa Reticular lamina
Basement Membrane
Function Structural foundation Selectively
permeable barrier Bind soluble ligands
guidance signal
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