Chapter 3 Cells Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Movements Through Cell Membranes Physical (Passive) Processes Require no cellular energy and include: Simple diffusion Facilitated diffusion Osmosis Filtration Physiological (Active) Processes Require cellular energy and include: Active transport Endocytosis Exocytosis Transcytosis

Simple Diffusion Movement of substances from regions of higher concentration to regions of lower concentration until equilibrium is reached Oxygen, carbon dioxide and lipid-soluble substances Permeable membrane Solute molecule W ater molecule A B A B A B (1) (2) (3) T ime

Animation: How Diffusion Works Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.

Facilitated Diffusion Diffusion across a membrane with the help of a channel or carrier molecule Glucose and amino acids The number of carrier molecules in the cell membrane limits the rate of this process Region of higher concentration Transported substance Region of lower concentration Protein carrier molecule Cell membrane

Animation: How Facilitated Diffusion Works Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.

Osmosis Special case of diffusion Movement of water through a selectively permeable membrane from regions of higher concentration to regions of lower concentration Water moves toward a higher concentration of solutes Selectively permeable membrane Protein molecule W ater molecule A A B B (1) (2) T ime

Animation: How Osmosis Works Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.

Osmosis and Osmotic Pressure Osmotic Pressure – ability of osmosis to generate enough pressure to move a volume of water Osmotic pressure increases as the concentration of nonpermeable solutes increases. (a) Isotonic – same osmotic pressure Cells placed in isotonic have no net gain or loss of water. Hypertonic – higher osmotic pressure (water loss) Cells placed in hypertonic solution lose water. Hypotonic – lower osmotic pressure (water gain) Cells placed in hypotonic solution gain water. (b) (c)

Filtration Smaller molecules are forced through porous membranes because of hydrostatic pressure Molecules leaving blood capillaries Blood pressure is a type of hydrostatic pressure Capillary wall Tissue fluid Blood pressure Blood flow Larger molecules Smaller molecules

Active Transport Carrier molecules transport substances across a membrane from regions of lower concentration to regions of higher concentration Requires energy (as much as 40% of cell’s energy supply) Sugars, amino acids, sodium ions, potassium ions, calcium ions, hydrogen ions etc. Carrier protein Binding site Region of higher concentration Cell membrane Region of lower concentration Phospholipid molecules Transported particle (a) Carrier protein with altered shape Cellular energy (b)

Active Transport: Sodium-Potassium Pump Active transport mechanism Creates balance by “pumping” three (3) sodium (Na+) OUT and two (2) potassium (K+) INTO the cell 3:2 ratio

Animation: How the Sodium-Potassium Pump Works Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.

Endocytosis Cell engulfs a substance that is too large to be transported by other means by forming a vesicle around the substance Three types: Pinocytosis – substance is mostly water Phagocytosis – substance is a solid Receptor-mediated endocytosis – requires the substance to bind to a membrane-bound receptor Cell membrane V esicle Nucleus Nucleolus

Endocytosis Cell membrane Particle Phagocytized particle Vesicle Nucleus Nucleolus Molecules outside cell Receptor-ligand combination V esicle Receptor protein Cell membrane Cell membrane indenting Cytoplasm (a) (b) (c) (d)

Exocytosis Reverse of endocytosis Substances in a vesicle fuse with cell membrane Contents released outside the cell Release of neurotransmitters from nerve cells Endoplasmic reticulum Golgi apparatus Nucleus

Receptor-mediated endocytosis Transcytosis Endocytosis followed by exocytosis Transports a substance rapidly through a cell HIV crossing a cell layer HIV-infected white blood cells Anal or vaginal canal V iruses bud HIV Receptor-mediated endocytosis Lining of anus or vagina (epithelial cells) Exocytosis Cell membrane Receptor-mediated endocytosis Virus infects white blood cells on other side of lining