5.3 Active Transport Across a Membrane The movement of molecules against their concentration gradient Movement from low to high concentration Movement is facilitated by carrier proteins Requires the expenditure of energy in the form of ATP Ex: sodium-potassium pump Uses ATP to move sodium ions out of the cells and potassium ions into the cell against their concentration gradients.

The Sodium-Potassium Pump Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. carrier protein Outside K+ K+ K+ K+ Na+ Na+ Na+ Na+ Na+ Inside Carrier has a shape that allows it to take up 3 Na+

The Sodium-Potassium Pump Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. carrier Outside K+ protein K+ K+ K+ K+ K+ K+ K+ Na+ Na+ Na+ Na+ Na+ Na+ Inside Na+ Carrier has a shape that allows it to take up 3 Na+. Na+ P ATP Na+ 2. ATP is split, and phosphate group attaches to carrier

The Sodium-Potassium Pump Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. carrier protein K+ Outside K+ K+ K+ K+ K+ K+ K+ Na+ Na+ Na+ Na+ Na+ Inside Carrier has a shape that allows it to take up 3 Na+. Na+ Na+ P Na+ ATP Na+ group attaches to carrier 2. ATP is split, and phosphate K+ Na+ Na+ Na+ K+ K+ K+ P Na+ Na+ 3. Change in shape results and outside the cell. causes carrier to release 3 Na+

The Sodium-Potassium Pump Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. carrier protein K+ Outside K+ K+ K+ K+ K+ K+ Na+ Na+ K+ Na+ Na+ Na+ Inside Na+ 1. Carrier has a shape that allows it to take up 3 Na+. Na+ Na+ P Na+ ATP Na+ 2. ATP is split, and phosphate group attaches to carrier. K+ Na+ Na+ Na+ K+ K+ K+ Na + Na + K + Na + K + P K + K + Na+ Na+ 3. Change in shape results and causes carrier to release 3 Na+ outside the cell. P Na+ Na+ allows it to take up 2K+. 4. Carrier has a shape that

The Sodium-Potassium Pump Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. carrier protein K+ Outside K+ K+ K+ K+ K+ K+ K+ Na+ Na+ Na+ Na+ Na+ Na+ Inside 1. Carrier has a shape that allows it to take up 3 Na+. Na+ Na+ P Na+ ATP Na+ 2. ATP is split, and phosphate group attaches to carrier. Na+ K+ Na+ K+ Na+ Na+ Na+ K+ Na+ K+ K+ K+ K+ K+ Na+ Na+ Na+ K+ Na+ K+ P P Na+ K+ Na+ K+ Na+ 5. Phosphate group is released from carrier. 3. Change in shape results and causes carrier to release 3 Na+ outside the cell. P Na+ Na+ allows it to take up 2 K+. 4. Carrier has a shape that

The Sodium-Potassium Pump Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. carrier protein K+ Outside K+ K+ K+ K+ Na+ Na+ K+ K+ K+ Na+ K K+ Na+ Na+ Na+ Na+ Na+ Na+ Inside it to take up 3 Na+. 1. Carrier has a shape that allows Na+ Na+ Na+ P Na+ Na+ K+ K+ ATP Na+ 6. Change in shape results and causes carrier to release 2K+ inside the cell. 2. ATP is split, and phosphate group attaches to carrier. Na+ K+ Na+ K+ Na+ Na+ Na+ K+ Na+ K+ K+ K+ K+ K+ Na+ Na+ K+ Na+ K+ P Na+ Na+ P Na+ K+ K+ Na+ 5. Phosphate group is released from carrier. 3. Change in shape results and outside the cell. causes carrier to release 3 Na+ P Na+ Na+ 4. Carrier has a shape that allows it to take up 2 K+.

Active Transport Across a Membrane Macromolecules are transported into or out of the cell inside vesicles via bulk transport Exocytosis – Vesicles fuse with plasma membrane and secrete contents Endocytosis – Cells engulf substances into a pouch which becomes a vesicle Phagocytosis – Large, solid material is taken in by endocytosis Pinocytosis – Vesicles form around a liquid or very small particles Receptor-Mediated Endocytosis– Specific form of pinocytosis using receptor proteins and a coated pit

Exocytosis Plasma membrane Outside Inside secretory vesicle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Plasma membrane Outside Inside secretory vesicle

Three Methods of Endocytosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. plasma membrane paramecium pseudopod vacuole forming vacuole 399.9 μm a. Phagocytosis vesicles forming solute vesicle b. Pinocytosis 0.5 μm receptor protein coated pit coated vesicle solute coated vesicle coated pit c. Receptor-mediated endocytosis

5.4 Modifications of Cell Surfaces Cell Surfaces in Animals Extracellular Matrix (ECM) Meshwork of proteins and polysaccharides in close connection with the cell that produced them Collagen – resists stretching Elastin – provides resilience to the ECM Integrin – play role in cell signaling Proteoglycans – regulate passage of material through the ECM to the plasma membrane

Animal Cell Extracellular Matrix Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Inside (cytoplasm) actin filament integrin elastin fibronectin proteoglycan collagen Outside (extracellular matrix)

Modifications of Cell Surfaces Cell Surfaces in Animals Junctions Between Cells Adhesion Junctions - Intercellular filaments between cells Desmosomes – internal cytoplasmic plaques Tight Junctions – form impermeable barriers Gap Junctions Plasma membrane channels are joined (allows communication)

Junctions Between Cells of the Intestinal Wall Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. plasma membranes cytoplasmic plaque Filaments of cytoskeleton adhesion proteins 100 nm intercellular space a. Adhesion junction plasma membranes light junction proteins intercellular space 50 nm b. Tight junction plasma membranes membrane channels intercellular space 20 nm c. Gap junction a: From Douglas E. Kelly, J. Cell Biol. 28 (1966): 51. Reproduced by copyright permission of The Rockefeller University Press; b: © David M. Phillips/Visuals Unlimited; c: Courtesy Camillo Peracchia, M.D.

Modifications of Cell Surfaces Plant Cell Walls Plants have a freely permeable cell wall, with cellulose as the main component Plasmodesmata penetrate the cell wall Each contains a strand of cytoplasm Allow passage of material between cells

Plasmodesmata plasmodesmata cell wall cell wall middle lamella plasma Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. plasmodesmata cell wall cell wall middle lamella plasma membrane plasma membrane cell wall cell wall cytoplasm cytoplasm plasmodesmata Cell 1 Cell 2 0.3mm © E.H. Newcomb/Biological Photo Service