CELL STRUCTURE & FUNCTION Sapling 3.3 CP Biology Paul VI Catholic High School

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.Basic Structure of Cell Membrane: A. Bilayer Lipid Membrane 1. Amphipathic (Polar) a. hydrophilic head (outside) b. hydrophobic tails (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. Temperature Effect: 1. High Temp-low viscosity high permeability 2. Low Temp-high viscosity low permeability

CELL STRUCTURE & FUNCTION D. 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 E. Models of Membranes 1. Davson-Danielli Model (1935) 2. Fluid Mosaic Model (1972) Fluid Mosaic model video

CELL STRUCTURE & FUNCTION

II. Components of Cell Membranes: A. Lipid Bilayer B. Membrane Proteins: 1. Peripheral 2. Integral

Integral Membrane Proteins – functions a. Allow Movement Thru Membrane (transport) b. Anchor Membranes (attach cell/cell, membrane/cytoskel.) c. Act as Receptors (“antennae”) d. Function as Enzymes (control reactions) e. Signal Transduction (communication) f. Cell-Cell Recognition

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”

CELL STRUCTURE & FUNCTION B. ANCHORING JUNCTIONS: Mechanically attaches cell to its neighbors …

CELL STRUCTURE & FUNCTION 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

Plasmodesmata

CELL STRUCTURE & FUNCTION Diffusion Diffusion video clip Osmosis -diffusion of water across a membrane –In osmosis, w ater travels from a solution of lower solute concentration to one of higher solute concentration Lower concentration of solute Higher concentration of solute Equal concentration of solute H2OH2O Solute molecule Selectively permeable membrane Water molecule Solute molecule with cluster of water molecules Net flow of water

CELL STRUCTURE & FUNCTION Plant cell H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O Plasma membrane (1) Normal (2) Lysed (3) Shriveled (4) Flaccid (5) Turgid (6) Shriveled (plasmolyzed) Isotonic solution Hypotonic solution Hypertonic solution Animal cell Video: Osmosis & Tonicity

CELL STRUCTURE & FUNCTION Movement Through Membranes 1. DIFFUSION: a. Moves with concentration gradient b. Dependent on selective permeability c. “Passive” process EquilibriumMembraneMolecules of dye Equilibrium –Small nonpolar molecules such as O 2 and CO 2 diffuse easily across the phospholipid bilayer of a membrane.

CELL STRUCTURE & FUNCTION 2. FACILITATED DIFFUSION a. Moves with conc. gradient b. Use channel protein c. “Passive” process 3. ACTIVE TRANSPORT a. Against conc. gradient b. Use carrier protein c. “Active” process – ATP energy

CELL STRUCTURE & FUNCTION

Channel – passive transport Active Transport REQUIRES ENERGY Moves against a gradient examples- Na-K Pump Maintain Osmotic balance (H 2 0) Maintain transmembrane electrical potential ATP

CELL STRUCTURE & FUNCTION Cotransport: Requires “carrier” protein Uniporter Symporter Antiporter

CELL STRUCTURE & FUNCTION Fluid outside cell Cytoplasm Protein Vesicle Vesicle forming Exocytosis Endocytosis Video

–Endocytosis can occur in three ways Phagocytosis Pinocytosis Receptor-mediated endocytosis Pseudopodium of amoeba Food being ingested Phagocytosis Pinocytosis Receptor-mediated endocytosis Material bound to receptor proteins PIT Cytoplasm Plasma membrane TEM 54,000  TEM 96,500  LM 230  Figure 5.19C CELL STRUCTURE & FUNCTION