Membrane Transport: Passive & Active See in your book See the handout

What is the difference between passive and active transport? Passive Transport #1: Diffusion Passive Transport #2: Osmosis Passive Transport #3: Passive Transport #4: Ion Channels Active Transport #1: Membrane/Ion Pumps Active Transport #2: Endocytosis Active Transport #3: Exocytosis

Key Definitions Homeostasis: maintaining the internal conditions of the cell Equilibrium: an equal amount of solutes on both sides of a membrane Potential energy vs. Kinetic energy Concentration gradient

Passive Transport #1: Diffusion Movement of molecules from area of [high] to [low] Caused by kinetic energy; molecules simply colliding. Ability to diffuse depends Size Polarity: like dissolves like Electric charge: opposites attract

Passive Transport #1: Diffusion Examples of diffusion: –CO2 and O2 are nonpolar. They can dissolve in lipids and diffuse across membrane –Small molecules can diffuse; what does this mean for large molecules like glucose?!

Passive Transport #2: Osmosis The diffusion of water Solution = solute in a solvent Water = “Universal Solvent” Direction of osmosis –Shortcut: Water flows to area of higher solute concentration.

Osmosis: Definitions of Solutions Hypotonic: Solution with lower [solutes] Hypertonic: Solution with high [solutes] Isotonic: Solution with equal [solutes] Pay attention to how a cell maintains equilibrium! (Pause to practice analyzing situations)

How Do Cells Deal With Osmosis? Isotonic? Vertebrates on land. Most sea organisms Most freshwater organisms are in hypotonic environments (esp if unicellular) –Where is water constantly moving? –Contractile vacuoles: to pump water out (NOTE: This requires energy!) Multicellular organisms will get rid of solutes instead

How Do Plants Deal With Osmosis? Generally, plants live in hypotonic environments. Turgor pressure: pressure that membrane exerts agains the cell wall as the cell fills with water. BUT Plants in hypertonic environments LOSE water Turgor pressure is…. Cell membrane …. This is PLASMOLYSIS (--> WILTING) See page 83 in your book

How Do Animals Deal With Osmosis? Some cells cannot withstand changes caused by osmosis. (No cell walls, no contractile vacuoles, no solute pumps*) In hyptertonic solutions, what happens? In hypotonic solutions, what happens? CYTOLYSIS See page 83 in your book (Red blood cells)

Passive Transport #3: If molecules are large or not lipid soluble Carrier proteins change shape, shield the molecule from nonpolar region of membrane –Specific to each molecule: glucose; each amino acid

Passive Transport #4: Ion Channels Ions like K+, Na+, Ca2+, Cl- are not lipid soluble Specific to each ion: Basic Ion ChannelBasic Ion Channel Some are “gated” –Membrane stretching –Electrical signals –Chemical signals Check out this potassium channel

Active Transport: What’s so special about active transport? Solute moves from [LOW] to [HIGH] Like going uphill, or upstream, this requires energy –“Up the concentration gradient” (Keep in mind the osmosis issues that require active transport)

Active Transport #1: Membrane Pumps a.k.a. Na-K Pump Acts like a carrier protein BUT ATP is needed to fuel the activity Animal cells need Na outside and K inside The ATP changes the shape of the protein… Basic Ion Pump How The Pump Works *Important for creating gradients leading to membrane potential aka voltages

Active Transport #2: Endocytosis To transport things INTO the cell. Phagocytosis : transport large particles or whole cells, bacteria and viruses (Cell eating) Pinocytosis : transport solutes or fluids (cell drinking) Membrane folds in and forms a vesicle Some vesicles fuse with lysosomes, which digest the contents. Paramecium! Neutrophils! Macrophages!Paramecium!Neutrophils!Macrophages!

Active Transport #3: Exocytosis Reverse of endocytosis To release large molecules made by the cell… –Proteins can be made by the ribosomes on rough ER, then packaged into vesicles by Golgi apparatus, and secreted –Endocrine system is a good example –To get rid of waste Paramecium Performing Exocytosis

Membrane Transport Passive Transport #1: Diffusion Passive Transport #2: Osmosis Passive Transport #3: Passive Transport #4: Ion Channels Active Transport #1: Membrane/Ion Pumps Active Transport #2: Endocytosis Active Transport #3: Exocytosis