Membrane Structure & Function AP Biology Chapter 7

Cellular membranes are fluid mosaics of lipids and proteins 7.1

Glyco- protein Carbohydrate Glycolipid Microfilaments of cytoskeleton EXTRACELLULAR SIDE OF MEMBRANE CYTOPLASMIC SIDE OF MEMBRANE Integral protein Peripheral proteins Cholesterol Fibers of extra- cellular matrix (ECM)

Membrane structure results in selective permeability 7.2

Selective Permeability  Cell membrane is “picky” about what is allowed to pass  Related to hydrophobic/hydrophilic nature of phospholipids  Transport proteins, carrier proteins, aquaporins assist in movement across membrane

Learning Targets – Membrane Function  I can explain how water will move if a cell is placed in an isotonic, hypotonic or hypertonic solution and predict the effect of these different environments on cells with and without cell walls.  I can explain how materials move into and out of cells both passively and actively  I can describe how a concentration gradient represents potential energy.  I can explain how electrochemical gradients are formed and function in cells.  I can describe how endocytosis and exocytosis move large molecules into and out of the cell respectively.

Passive transport is diffusion of a substance across a membrane with no energy investment 7.3

Passive Transport  Movement of materials across membrane without using energy  With the concentration gradient  3 types 1. Diffusion 2. Osmosis 3. Facilitated diffusion

1. Diffusion  Movement of molecules from high to low concentration  Ex: O 2, CO 2

2. Osmosis  Movement of water across a selectively permeable membrane  Passive transport – high to low concentration, no energy required  3 osmotic environments

A. Hypotonic  Higher concentration of water/lower concentration of solute outside the cell  Water moves into the cell  Animal cells – cytolysis  Contractile vacuole (Paramecium)  Plant cells – turgor pressure

B. Hypertonic  Lower concentration of water/higher concentration of solute outside of the cell  Water moves out of the cell  Animal cells – plasmolysis  Plant cells – plasmolysis

C. Isotonic  Concentration of water and solute is equal on both sides of the membrane  No net movement of water (still moves)  Animal cells – normal  Plant cells – flaccid

3. Facilitated Diffusion  Transport proteins open to allow diffusion of molecules too large to fit otherwise 1. Channel proteins  Channel allows molecules to pass 2. Carrier proteins  Change shape to bind and allow molecules to pass

Active transport uses energy to move substances against their gradients 7.4

Active Transport  Against concentration gradient, therefore requiring energy (ATP)  2 types  Ion pumps  Cotransport

Ion Pumps  Example: sodium-potassium pump  Establish gradient across the membrane for neurons to “fire”  ATP energy used to:  move 3 Na + ions out of the cell while simultaneously moving 2 K + ions into the cell  Animation Animation

Cotransport  Membrane protein enables the “downhill” diffusion of one molecule to drive the “uphill” transport of another  Sucrose transport in plants Sucrose transport in plants

Bulk transport across the plasma membrane occurs by exocytosis and endocytosis 7.5

Endocytosis  Bringing materials into cell 1. Receptor- mediated 2. Pinocytosis 3. Phagocytosis  Animation Animation

Exocytosis  Secreting materials out of cell  Animation Animation