Cell Membrane

Structure: made of a phospholipid bilayer and proteins

Hydrophilic phosphate head replaces one of the three lipid tails of a triglyceride

Hydrophobic lipid tails turn toward the inside of the membrane

Proteins in the membrane serve various functions:

Carrier proteins transport materials across the membrane.

Channel proteins allow materials to pass in and out of the membrane.

Cell surface markers identify the cell

Glycoproteins are made of carbohydrates attached to proteins.

Glycolipids are made of carbohydrates attached to lipids.

Equilibrium: even distribution of molecules

Solution: mixture in which solute particles are evenly distributed in a solution.

Solute: substance dissolved a solvent.

Solvent: liquid in which solute is dissolved.

Requires no energy

Diffusion: random movement of molecules from a region of high concentration to low concentration.

Factors affecting rate of diffusion

concentration

temperature

pressure

Increase in any of these factors increases rate of diffusion

Osmosis: random movement of water molecules from a region of high concentration to low concentration across a membrane.

Isotonic: concentration of solutes is equal.

Hypertonic: concentration of solutes is greater.

Plasmolysis: cell shrivels as it loses water.

Hypotonic: concentration of solutes is lower.

Cytolysis: animal cell bursts as water enters the cell.

Turgor pressure: increase of water pressure inside a plant cell.

Facilitated Diffusion: movement of molecules from a region of high concentration to low concentration using a helper molecule.

Example: glucose must have a protein helper (which is specific to glucose) to help it move into the cell.

Energy is required to move materials against the concentration gradient (from a region of low concentration to a region of high concentration).

Pumps: proteins in the membrane are specific for molecules being carried across the cell membrane.

Iodine moving into thyroid cells.

Sodium potassium pump involved in nerve impulse.

Endocytosis: taking material into the cell.

Pinocytosis: cell drinking; taking in small particles or liquids.

Phagocytosis: cell eating; taking in large particles.

Exocytosis: putting material out of the cell.