1. Chapter 8 Membrane Structure & Function
Fluid mosaic model

2. Membrane structure, I Selective permeability
Amphipathic~ hydrophobic & hydrophilic regions
1935 Davson Danielli sandwich model
Singer-Nicolson: fluid mosaic model

3. Membrane Structure
A specialized preparation technique, freeze-fracture supports the fluid mosaic model.

4. Membrane structure, II Phospholipids~ membrane fluidity
Cholesterol~ membrane stabilization
“Mosaic” Structure~
Integral proteins~ transmembrane proteins
Peripheral proteins~ surface of membrane
Membrane carbohydrates ~ cell to cell recognition; oligosaccharides (cell markers); glycolipids; glycoproteins

5. Membrane structure, III
Membrane protein function: •transport •enzymatic activity •signal transduction •intercellular joining •cell-cell recognition •ECM attachment

6. Membrane traffic
Diffusion~ tendency of any molecule to spread out into available space
Concentration gradient
Passive transport~ diffusion of a substance across a biological membrane
Osmosis~ the diffusion of water across a selectively permeable membrane

7. Water balance Osmoregulation~ control of water balance
Hypertonic~ higher concentration of solutes
Hypotonic~ lower concentration of solutes
Isotonic~ equal concentrations of solutes
Cells with Walls:
Turgid (very firm)
Flaccid (limp)
Plasmolysis~ plasma membrane pulls away from cell wall

8. Specialized Transport
Transport proteins
Facilitated diffusion~ passage of molecules and ions with transport proteins across a membrane down the concentration gradient
Active transport~ movement of a substance against its concentration gradient with the help of cellular energy

9. Types of Active Transport
Sodium-potassium pump
Exocytosis~ secretion of macromolecules by the fusion of vesicles with the plasma membrane
Endocytosis~ import of macromolecules by forming new vesicles with the plasma membrane •phagocytosis •pinocytosis •receptor-mediated endocytosis (ligands)

10. Exocytosis transport large molecules out
transport vesicle budded from the Golgi apparatus is moved by the cytoskeleton to the plasma membrane.
When the two membranes come in contact, the bilayers fuse and spill the contents to the outside

11. Endocytosis 1. phagocytosis, “cellular eating”.
a cell brings in macromolecules and particulate matter by forming new vesicles from the plasma membrane
3 types:
1. phagocytosis, “cellular eating”.
the cell engulfs a particle by extending pseudopodia around it and packaging it in a large vacuole.

12. Endocytosis
2. pinocytosis, “cellular drinking”, a cell creates a vesicle around a droplet of extracellular fluid
This is a non-specific process.

13. Endocytosis
3. Receptor-mediated endocytosis is very specific in what substances are being transported
triggered when extracellular substances bind to special receptors, ligands, on the membrane surface, especially near coated pits
triggers the formation of a vesicle