Chapter 8~ Membrane Structure & Function

Membrane structure, I

Selective permeability

Amphipathic~ hydrophobic & hydrophilic regions

Singer-Nicolson: fluid mosaic model

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

Membrane structure, III

Membrane protein function: • transport •enzymatic activity •signal transduction •intercellular joining •cell-cell recognition •ECM attachment

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

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

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

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)