Chapter 6.3 : Membranes regulate the traffic of molecules

1. Chapter 6.3: Membranes regulate the traffic of molecules College Prep Biology Mr. Martino

2. 6.3Cell Membranes • Cell membranes make the E in chemical bonds available for metabolic reactions • Kinds and amounts of substances different on either side of membrane – membrane is selectively permeable • CO2, O2, water, and small nonpolar molecules move easily across • Large, polar molecules and ions do not move freely across • These require various proteins

3. Concentration Gradients • Brownian Motion – continuousrandom movement of particles due to temp. differences • Concentration gradient: the difference in conc. of particles on one side of a membrane as opposed to the other

4. Diffusion • Diffusion: the tendency for particles to move from areas of high concentration to areas of low conc. • Molecules naturally move “with” conc. Gradient • Diffusion is fastest when gradient is steep

5. Active transport: requires E to move substances across a membrane • Transport protein pumps the substance against the conc. gradient • Usually use ATP

7. Movement of Water • Osmosis:the diffusion (passive transport) of water • Hypertonic Solution:has a higher conc. of solutes than the cell • Water will leave cells and cells will shrivel • Hypotonic Solution: had a lower conc. of solutes than the cell • Water will rush into cells and cells will swell

8. Turgor (hydrostatic) pressure: the internal force pushing outward in plant cells • Cell wall prevents the uptake of too much water • Isotonic Solution: the conc. of particles inside the cell is = to the conc. of the particles outside the cell • Movement continues – just no net movement

10. Endocytosis and Exocytosis • Exocytosis: process of how cells export bulky materials from the cytoplasm • Ex. Tear and insulin formation • Endocytosis: process of how cells import macromolecules • Phagocytosis: cellular eating • Pinocytosis: cellular drinking • Receptor-mediated endocytosis: highly specific due to receptor proteins