Biology Sylvia S. Mader Michael Windelspecht Chapter 5B Membrane Structure and Function Lecture Outline Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes.

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Passive Transport Across a Membrane  Facilitated Transport Movement of molecules that cannot pass directly through the membrane lipids These molecules must combine with carrier proteins to move across the membrane Follow concentration gradient, moving from high concentration to low concentration 3

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. solute Outside Inside plasma membrane carrier protein Facilitated Transport

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5.3 Active Transport Across a Membrane  Active Transport 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. 6

The Sodium-Potassium Pump 7 carrier protein 1. Carrier has a shape that allows it to take up 3 Na Carrier has a shape that allows it to take up 2 K ATP is split, and phosphate group attaches to carrier. 3. Change in shape results and causes carrier to release 3 Na + outside the cell. 5. Phosphate group is released from carrier. Outside Inside ATP K+K+ K+K+ K+K+ K+K+ P P P P Na + K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6. Change in shape results and causes carrier to release 2K + inside the cell. K+K+ K K+K+ Na + K+K+

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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 11

Exocytosis 12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Outside Plasma membrane Inside secretory vesicle

Three Methods of Endocytosis 13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. pseudopod paramecium vacuole forming vesicles forming coated pit coated vesicle solute a. Phagocytosis b. Pinocytosis vacuole coated vesicle plasma membrane receptor protein coated pit c. Receptor-mediated endocytosis vesicle 0.5 μmμm μmμm

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