1. Membrane Structure & Function
Chapter 7:
Membrane Structure & Function

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

3. Membrane structure, II Phospholipids: membrane fluidity
Cholesterol: membrane stabilization
“Mosaic” Structure:
Integral proteins: transmembrane
Peripheral proteins: surface
Membrane carbohydrates: cell-cell recognition
Oligosaccharides (markers)
Glycolipids, glycoproteins

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

6. Animation: Membrane Selectivity
Membrane traffic
Passive transport: diffusion of a substance across a biological membrane without Energy
Diffusion: tendency of molecules to move from areas of high to low conc.
Concentration gradient
Osmosis: the diffusion of water across a selectively permeable membrane
Animation: Membrane Selectivity
Animation: Diffusion

8. Water balance Osmoregulation: control of water balance
Hypertonic: higher concentration of solutes
Solutes bind water, lower water potential (conc.)
Water will move into the hyper solution to dilute it (increase its water conc.)
Hypotonic: lower concentration of solutes
Has higher water potential, more free water, loses water
Isotonic: equal concentrations of solutes

9. Video: Paramecium Vacuole
Water Balance Cont.
Pay attention to reference point for –tonics
Saltwater is hypertonic to fish cells, so water leaves the cells
BUT fish’s cells are hypotonic to saltwater as well
Water moves to lower water potential (MORE concentrated solution)
More solute = lower potential
Video: Chlamydomonas
Video: Paramecium Vacuole

10. Water Balance Cont. Cells with Cell Walls:
Turgid (very firm, pressurized) …
Due to hypertonic cells
Flaccid (limp) …
Due to hypotonic cells
Plasmolysis:
plasma membrane pulls away from cell wall (bad)
Video: Plasmolysis
Video: Turgid Elodea
Animation: Osmosis

12. Specialized Transport
Transport proteins
Facilitated diffusion:
movement of ions and molecules down the conc. gradient via transport proteins
Active transport:
movement of substance against the conc. gradient with the help of cellular energy

14. Types of Active Transport
Sodium-potassium pump
Exocytosis: secrete macromolecules via fusing vesicles w/ plasma membrane
Endocytosis: import macromolecules by forming new vesicles w/ plasma membrane
phagocytosis
pinocytosis
receptor-mediated endocytosis (ligands)
Active Transport
Exocytosis
Phagocytosis
Exo and Endocytosis Introduction
Receptor-Mediated Endocytosis