BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Neil A. Campbell Jane B. Reece Lawrence G. Mitchell Martha R. Taylor From PowerPoint ® Lectures for Biology: Concepts & Connections CHAPTER 5 The Working Cell Modules 5.10 – 5.21

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Membranes organize the chemical reactions making up metabolism 5.10 Membranes organize the chemical activities of cells MEMBRANE STRUCTURE AND FUNCTION Cytoplasm   Figure 5.10

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Membranes are selectively permeable –They control the flow of substances into and out of a cell Membranes can hold teams of enzymes that function in metabolism

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Phospholipids are the main structural components of membranes They each have a hydrophilic head and two hydrophobic tails 5.11 Membrane phospholipids form a bilayer Head Symbol Tails Figure 5.11A

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In water, phospholipids form a stable bilayer Figure 5.11B Hydrophilic heads Hydrophobic tails Water –The heads face outward and the tails face inward

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Phospholipid molecules form a flexible bilayer –Cholesterol and protein molecules are embedded in it –Carbohydrates act as cell identification tags 5.12 The membrane is a fluid mosaic of phospholipids and proteins

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The plasma membrane of an animal cell Fibers of the extracellular matrix Figure 5.12 Glycoprotein Carbohydrate (of glycoprotein) Microfilaments of the cytoskeleton Phospholipid Cholesterol Proteins CYTOPLASM Glycolipid

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Some membrane proteins form cell junctions Others transport substances across the membrane 5.13 Proteins make the membrane a mosaic of function Transport Figure 5.13

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Many membrane proteins are enzymes Figure 5.13 Some proteins function as receptors for chemical messages from other cells –The binding of a messenger to a receptor may trigger signal transduction Enzyme activitySignal transduction Messenger molecule Receptor Activated molecule

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In passive transport, substances diffuse through membranes without work by the cell –They spread from areas of high concentration to areas of lower concentration 5.14 Passive transport is diffusion across a membrane EQUILIBRIUM Molecule of dye Figure 5.14A & B Membrane EQUILIBRIUM

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In osmosis, water travels from an area of lower solute concentration to an area of higher solute concentration 5.15 Osmosis is the passive transport of water Hypotonic solution Figure 5.15 Solute molecule HYPOTONIC SOLUTION Hypertonic solution Selectively permeable membrane HYPERTONIC SOLUTION Selectively permeable membrane NET FLOW OF WATER Solute molecule with cluster of water molecules Water molecule

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution –The control of water balance (osmoregulation) is essential for organisms 5.16 Water balance between cells and their surroundings is crucial to organisms ISOTONIC SOLUTION Figure 5.16 HYPOTONIC SOLUTION HYPERTONIC SOLUTION (1) Normal (4) Flaccid (2) Lysing (5) Turgid (3) Shriveled (6) Shriveled ANIMAL CELL PLANT CELL Plasma membrane

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Small nonpolar molecules diffuse freely through the phospholipid bilayer Many other kinds of molecules pass through selective protein pores by facilitated diffusion 5.17 Transport proteins facilitate diffusion across membranes Figure 5.17 Solute molecule Transport protein

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Transport proteins can move solutes across a membrane against a concentration gradient –This is called active transport –Active transport requires ATP 5.18 Cells expend energy for active transport

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Active transport in two solutes across a membrane Figure 5.18 Transport protein 1 FLUID OUTSIDE CELL First solute First solute, inside cell, binds to protein Phosphorylated transport protein 2 ATP transfers phosphate to protein 3 Protein releases solute outside cell 4 Second solute binds to protein Second solute 5 Phosphate detaches from protein 6 Protein releases second solute into cell

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings To move large molecules or particles through a membrane –a vesicle may fuse with the membrane and expel its contents (exocytosis) 5.19 Exocytosis and endocytosis transport large molecules Figure 5.19A FLUID OUTSIDE CELL CYTOPLASM

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –or the membrane may fold inward, trapping material from the outside (endocytosis) Figure 5.19B

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Three kinds of endocytosis Figure 5.19C Pseudopod of amoeba Food being ingested Plasma membrane Material bound to receptor proteins PIT Cytoplasm

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors 5.20 Connection: Faulty membranes can overload the blood with cholesterol Figure 5.20 LDL PARTICLE Phospholipid outer layer Protein Cholesterol Plasma membrane CYTOPLASM Receptor protein Vesicle

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Enzymes and membranes are central to the processes that make energy available to the cell Chloroplasts carry out photosynthesis, using solar energy to produce glucose and oxygen from carbon dioxide and water Mitochondria consume oxygen in cellular respiration, using the energy stored in glucose to make ATP 5.21 Chloroplasts and mitochondria make energy available for cellular work

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Nearly all the chemical energy that organisms use comes ultimately from sunlight Chemicals recycle among living organisms and their environment Figure 5.21 Sunlight energy Chloroplasts, site of photosynthesis CO 2 + H 2 O Glucose + O 2 Mitochondria sites of cellular respiration (for cellular work) Heat energy