Chapter 5 - The Plasma Membrane

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Presentation transcript:

Chapter 5 - The Plasma Membrane V. Plasma Membrane - all cells have them - complex, dynamic structures, not passive - differentially permeable

B. Structure (Fluid mosaic model) (10nm.) A. Functions 1. Regulates the movement of molecules into and out of the cell 2. Site of cell recognition and communication B. Structure (Fluid mosaic model) (10nm.) 1. Phospholipids a. 5 - 10 different types b. Most common = phosphotidylcholine c. Membrane fusion easily accomplished 2. Cholesterol - decreases fluidity of membrane

Membrane Fluidity Why is it that membrane phospholipids drift laterally, and rarely flip?

How is this fluidity maintained? Kinks in unsaturated fatty acid tails of phospholipids. Cholesterol

4. Glycoproteins and glycolipids - cell recognition a. Integral proteins -part or all the way through membrane (some move like icebergs) b. Peripheral proteins - usually bound to integral proteins (inside surface) 4. Glycoproteins and glycolipids - cell recognition - external surface oligosaccharides (<15 units)

C. Transport across the membrane 1. Diffusion movement of molecules down the concentration gradient passive process - energy from kinetic energy of molecules a. Channel proteins - aqueous channel for ions, gated

b. Facilitated diffusion - molecule binds to protein and is transported across membrane i. Protein changes its shape ii. Specificity Animation

c. Osmosis - diffusion of water through a selectively permeable membrane

Know and understand these terms = isotonic, hypertonic, hypotonic, water potential, turgor, plasmolysis

Osmotic Pressure

2. Active transport a. Movement of molecules up the concentration gradient b. Requires energy (ATP) c. E.g. sodium-potassium pump

3. Cotransport - transport of one solute coupled to transport of another

5. Exocytosis - waste removal or secretion 4. Endocytosis - movement of large molecules (proteins, polysaccharides) through membrane by forming vesicles a. Phagocytosis - chunks b. Pinocytosis - droplets c. Receptor-mediated endocytosis - receptor-covered depressions (coated pits) form coated vesicles (“ligand”=molecule grabbed on to) 5. Exocytosis - waste removal or secretion

Receptor-mediated Endocytosis