Chapter 5 The Working Cell Power Point Lectures

Chapter 5 The Working Cell Power. Point Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

5. 14 Passive transport is diffusion across a membrane • Diffusion is the tendency for particles to spread out evenly in an available space – From an area of high concentration to an area of low concentration • Passive transport across membranes occurs when a molecule diffuses down a concentration gradient • Small nonpolar molecules such as O 2 and CO 2 diffuse easily across the phospholipid bilayer of a membrane Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

LE 5 -14 a Molecules of dye Membrane Equilibrium

LE 5 -14 b Equilibrium

Animation: Diffusion Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

5. 15 Transport proteins may facilitate diffusion across membranes • In facilitated diffusion – Transport proteins that span the membrane bilayer help substances diffuse down a concentration gradient • To transport the substance, a transport protein may – Provide a pore for passage – Bind the substance, change shape, and then release the substance Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

LE 5 -15 Solute molecule Transport protein

5. 16 Osmosis is the diffusion of water across a membrane • In osmosis water, molecules diffuse across a selectively permeable membrane – From an area of low solute concentration – To an area of high solute concentration – Until the solution is equally concentrated on both sides of the membrane • The direction of movement is determined by the difference in total solute concentration – Not by the nature of the solutes Animation: Osmosis Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

LE 5 -16 Lower concentration of solute Higher concentration of solute Equal concentration of solute H 2 O Solute molecule Selectively permeable membrane Water molecule Solute molecule with cluster of water molecules Net flow of water

5. 17 Water balance between cells and their surroundings is crucial to organisms • Osmoregulation is the control of water balance • Tonicity is the tendency of a cell to lose or gain water in solution – Isotonic solution: solute concentration is the same in the cell and in the solution • No osmosis occurs • Animal cell volume remains constant; plant cell becomes flaccid Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

– Hypotonic solution: solute concentration is greater in the cell than in the solution • Cell gains water through osmosis • Animal cell lyses; plant cell becomes turgid – Hypertonic solution: solute concentration is lower in the cell than in the solution • Cell loses water through osmosis • Animal cell shrivels; plant cell plasmolyzes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

LE 5 -17 Isotonic solution Hypotonic solution H 2 O Hypertonic solution H 2 O Animal cell (2) Lysed (1) Normal H 2 O (3) Shriveled Plasma membrane H 2 O Plant cell (4) Flaccid (5) Turgid (6) Shriveled (plasmolyzed)

Video: Plasmolysis Video: Turgid Elodea Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

5. 18 Cells expend energy for active transport • Active transport requires energy to move solutes against a concentration gradient – ATP supplies the energy – Transport proteins move solute molecules across the membrane Animation: Active Transport Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

LE 5 -18 Transport protein ATP Solute binding P ADP Phosphorylation Protein changes shape Transport P Phosphate detaches P Protein reversion

5. 19 Exocytosis and endocytosis transport large molecules • To move large molecules or particles through a cell membrane – A vesicle may fuse with the membrane and expel its contents outside the cell (exocytosis) – Membranes may fold inward, enclosing material from the outside (endocytosis) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

5. 19 Exocytosis and endocytosis transport large molecules • To move large molecules or particles through a cell membrane – A vesicle may fuse with the membrane and expel its contents outside the cell (exocytosis) – Membranes may fold inward, enclosing material from the outside (endocytosis) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

LE 5 -19 a Fluid outside cell Vesicle Protein Cytoplasm

LE 5 -19 b Vesicle forming

• Endocytosis can occur in three ways – Phagocytosis ("cell eating") – Pinocytosis ("cell drinking") – Receptor-mediated endocytosis Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

LE 5 -19 c Food being ingested LM 230 Pseudopodium of amoeba Phagocytosis Pinocytosis Material bound to receptor proteins PIT Cytoplasm Receptor-mediated endocytosis TEM 96, 500 TEM 54, 000 Plasma membrane

Animation: Receptor-Mediated Endocytosis Animation: Exocytosis and Endocytosis Introduction Animation: Exocytosis Animation: Pinocytosis Animation: Phagocytosis Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

CONNECTION 5. 20 Faulty membranes can overload the blood with cholesterol • Cholesterol is carried in the blood by lowdensity lipoprotein (LDL) particles • Normally, body cells take up LDLs by receptormediated endocytosis • Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors – People with hypercholesterolemia have more than twice the normal level of blood cholesterol Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

LE 5 -20 Phospholipid outer layer LDL particle Vesicle Cholesterol Protein Plasma membrane Receptor protein Cytoplasm