Chapter 6.3: Membranes regulate the traffic of

molecules

College Prep BiologyMr. Martino

6.3 Cell 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

Concentration Gradients Brownian Motion –

continuous random 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

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

Active transport: requires E to move substances across a membrane Transport

protein pumps the substance against the conc. gradient

Usually use ATP

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

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

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