CELL STRUCTURE & FUNCTION Dr. Michael C. Potter Paul VI Catholic High School 2006

CELL STRUCTURE & FUNCTION 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)

CELL STRUCTURE & FUNCTION

I.Structure of Cell Membrane: A. Bilayer Lipid Membrane 1. Amphipathic (Polar) a. hydrophilic head (outside) b. hydrophobic head (inside)

CELL STRUCTURE & FUNCTION

2. Type of Phospholipid determine permeability a. Double bond vs. Single bond b. Long tail vs. Short tail B. Proteins: Multiple Function/Structure

CELL STRUCTURE & FUNCTION

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

CELL STRUCTURE & FUNCTION 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)

CELL STRUCTURE & FUNCTION

II. Components of Cell Membranes: A. Lipid Bilayer B. Membrane Proteins: 1. Integral Membrane Proteins a. Three Domains: Cytosolic Face Exoplasmic Face Membrane Spanning Domain

CELL STRUCTURE & FUNCTION

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

CELL STRUCTURE & FUNCTION B. Membrane Proteins: 1. Integral Membrane Proteins: h. Types: 1. Transmembrane Proteins 2. Membrane Associated Proteins 3. Lipid-Linked Proteins 4. Protein Attached

CELL STRUCTURE & FUNCTION

Ex. Of “Glycocalyx”

CELL STRUCTURE & FUNCTION B. MEMBRANE PROTEINS: Transmembrane Proteins: a. Single Pass: (Glycophorin in RBC) b. Multipass: Channels, Pores, Gates β- Barrel Porin Proteins

CELL STRUCTURE & FUNCTION

MEMBRANE PORE PROTEIN

CELL STRUCTURE & FUNCTION

B. MEMBRANE PROTEINS: Membrane Associated Proteins: Exoplasmic Face: Anchors Receptors Signaling Proteins Attachment Proteins Recognition Proteins

CELL STRUCTURE & FUNCTION CELL RECOGNITION (IDENT.) PROTEIN

CELL STRUCTURE & FUNCTION

B. MEMBRANE PROTEINS: Membrane Associated Proteins: Cytosolic Face: Attachment Proteins (Spectrin-RBC’s) Anchors Structural Proteins Signaling Proteins

CELL STRUCTURE & FUNCTION 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

CELL STRUCTURE & FUNCTION Occluding junction (Tight Junction)

CELL STRUCTURE & FUNCTION 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

CELL STRUCTURE & FUNCTION ANCHORING JUNCTION

CELL STRUCTURE & FUNCTION III. CELL JUNCTIONS: B. ANCHORING JUNCTIONS: Focal Adhesions Hemidesmosomes Bind cells to extracellular matrix (integrin proteins)

CELL STRUCTURE & FUNCTION ANCHORING JUNCTION

CELL STRUCTURE & FUNCTION 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)

CELL STRUCTURE & FUNCTION Communicating Junction

CELL STRUCTURE & FUNCTION Communicating Junction

CELL STRUCTURE & FUNCTION PLASMODESMATA

CELL STRUCTURE & FUNCTION PLASMODESMATA

CELL STRUCTURE & FUNCTION

SYMPORTER

CELL STRUCTURE & FUNCTION 1. Integral Membrane Proteins (cont’d) b. Movement through Membranes - Active Transport REQUIRES ENERGY Moves against a gradient Na-K Pump Maintains Osmotic balance Maintains transmembrane electrical potential

CELL STRUCTURE & FUNCTION ACTIVE TRANSPORT

CELL STRUCTURE & FUNCTION 2. Lipid-Anchored Membrane Protein: Extend partially thru membrane Bound to one or more lipids 3. Peripheral (exterior) Proteins: Do not interact with hydrophobic core Localized to cytosolic or exoplasmic face

CELL STRUCTURE & FUNCTION C. Network of Support Fibers 1. Often Intermediate Filaments a. Vimentins b. Desmins c. Spectrin: determines shape of cell, whereas… d. Clathrins: anchor proteins to certain sites.

CELL STRUCTURE & FUNCTION D. Exterior Protein & Glycoprotein 1. Glycocalyx 2. Cell identity markers

CELL STRUCTURE & FUNCTION Kinds of Membrane Proteins 1. Transport Channels: a. Single Pass b. Multipass 2. Enzymes a. Attached to membrane b. Function on interior of membrane 3. Cell Surface Receptor a. Act as “antennae”

CELL STRUCTURE & FUNCTION Kinds of Membrane Proteins 4. Cell Surface Identity Markers 5. Cell Adhesion Proteins 6. Attachments to Cytoskeleton Linking proteins

CELL STRUCTURE & FUNCTION Movement Through Membranes 1. DIFFUSION: a. Moves with gradient b. Dependent on selective permeability c. May utilize channels or pores e.g. movement of ions d. “Passive” process

CELL STRUCTURE & FUNCTION 2. FACILITATED DIFFUSION a.

CELL STRUCTURE & FUNCTION

1.Integral Membrane Proteins (cont’d) b. Movement through Membranes - Cotransport: Requires transmembrane protein or “carrier” protein Uniporter Symporter Antiporter Secondary “Active Transport”

CELL STRUCTURE & FUNCTION

COTRANSPORT

CELL STRUCTURE & FUNCTION