CHAPTER 5 The Working Cell

1. CHAPTER 5The Working Cell Modules 5.10 – 5.21

2. MEMBRANE STRUCTURE AND FUNCTION 5.10 Membranes organize the chemical activities of cells • Membranes organize the chemical reactions making up metabolism   Cytoplasm Figure 5.10

3. They control the flow of substances into and out of a cell • Membranes can hold teams of enzymes that function in metabolism • Membranes are selectively permeable

4. 5.11 Membrane phospholipids form a bilayer Head • Phospholipids are the main structural components of membranes • They each have a hydrophilic head and two hydrophobic tails Symbol Tails Figure 5.11A

5. The heads face outward and the tails face inward • In water, phospholipids form a stable bilayer Water Hydrophilicheads Hydrophobictails Water Figure 5.11B

6. 5.12 The membrane is a fluid mosaic of phospholipids and proteins • Phospholipid molecules form a flexible bilayer • Cholesterol and protein molecules are embedded in it • Carbohydrates act as cell identification tags

7. The plasma membrane of an animal cell Glycoprotein Carbohydrate (of glycoprotein) Fibers of the extracellular matrix Glycolipid Phospholipid Cholesterol Microfilaments of the cytoskeleton Proteins CYTOPLASM Figure 5.12

8. 5.13 Proteins make the membrane a mosaic of function • Some membrane proteins form cell junctions • Others transport substances across the membrane Transport Figure 5.13

9. Some proteins function as receptors for chemical messages from other cells • The binding of a messenger to a receptor may trigger signal transduction • Many membrane proteins are enzymes Messenger molecule Receptor Activated molecule Enzyme activity Signal transduction Figure 5.13

10. 5.14 Passive transport is diffusion across a membrane Molecule of dye Membrane EQUILIBRIUM • In passive transport, substances diffuse through membranes without work by the cell • They spread from areas of high concentration to areas of lower concentration EQUILIBRIUM Figure 5.14A & B

11. 5.15 Osmosis is the passive transport of water Hypotonicsolution Hypertonic solution • In osmosis, water travels from an area of lower solute concentration to an area of higher solute concentration Selectivelypermeablemembrane Solutemolecule HYPOTONIC SOLUTION HYPERTONIC SOLUTION Water molecule Selectivelypermeablemembrane Solute molecule with cluster of water molecules Figure 5.15 NET FLOW OF WATER

12. 5.16 Water balance between cells and their surroundings is crucial to organisms • 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 ISOTONIC SOLUTION HYPOTONIC SOLUTION HYPERTONIC SOLUTION ANIMALCELL (1) Normal (2) Lysing (3) Shriveled Plasmamembrane PLANTCELL (4) Flaccid (5) Turgid (6) Shriveled Figure 5.16

13. 5.17 Transport proteins facilitate diffusion across membranes • Small nonpolar molecules diffuse freely through the phospholipid bilayer • Many other kinds of molecules pass through selective protein pores by facilitated diffusion Solutemolecule Transportprotein Figure 5.17

14. 5.18 Cells expend energy for active transport • Transport proteins can move solutes across a membrane against a concentration gradient • This is called active transport • Active transport requires ATP

15. FLUIDOUTSIDECELL Phosphorylated transport protein Transportprotein • Active transport in two solutes across a membrane Firstsolute 1 First solute, inside cell, binds to protein 2 ATP transfers phosphate to protein 3 Protein releases solute outside cell Second solute 4 Second solute binds to protein 5 Phosphate detaches from protein 6 Protein releases second solute into cell Figure 5.18

16. 5.19 Exocytosis and endocytosis transport large molecules • To move large molecules or particles through a membrane • a vesicle may fuse with the membrane and expel its contents (exocytosis) FLUID OUTSIDE CELL CYTOPLASM Figure 5.19A

17. or the membrane may fold inward, trapping material from the outside (endocytosis) Figure 5.19B

18. Three kinds of endocytosis Pseudopod of amoeba Food being ingested Plasma membrane Material bound to receptor proteins PIT Cytoplasm Figure 5.19C

19. 5.20 Connection: Faulty membranes can overload the blood with cholesterol • Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors Phospholipid outer layer LDL PARTICLE Receptor protein Protein Cholesterol Plasma membrane Vesicle CYTOPLASM Figure 5.20

20. 5.21 Chloroplasts and mitochondria make energy available for cellular work • 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

21. Sunlight energy Chloroplasts,site of photosynthesis • Nearly all the chemical energy that organisms use comes ultimately from sunlight CO2+H2O Glucose+O2 Mitochondriasites of cellularrespiration • Chemicals recycle among living organisms and their environment (for cellular work) Heat energy Figure 5.21