CHAPTER 4 A Tour of the Cell

1. CHAPTER 4A Tour of the Cell Modules 4.6 – 4.14

2. ORGANELLES OF THE ENDOMEMBRANE SYSTEM 4.6 The nucleus is the cell’s genetic control center • The largest organelle is usually the nucleus • The nucleus is separated from the cytoplasm by the nuclear envelope • The nucleus is the cellular control center • It contains the DNA that directs the cell’s activities

3. NUCLEUS Chromatin Two membranesof nuclearenvelope Nucleolus Pore ROUGHENDOPLASMICRETICULUM Ribosomes Figure 4.6

4. 4.7 Overview: Many cell organelles are related through the endomembrane system • The endomembrane system is a collection of membranous organelles • These organelles manufacture and distribute cell products • The endomembrane system divides the cell into compartments • Endoplasmic reticulum (ER) is part of the endomembrane system

5. Transport vesiclebuds off 4 Ribosome Secretory(glyco-) proteininside transportvesicle Sugarchain 3 Glycoprotein 1 2 ROUGH ER Polypeptide 4.8 Rough endoplasmic reticulum makes membrane and proteins • The rough ER manufactures membranes • Ribosomes on its surface produce proteins Figure 4.8

6. 4.9 Smooth endoplasmic reticulum has a variety of functions • Smooth ER synthesizes lipids • In some cells, it regulates carbohydrate metabolism and breaks down toxins and drugs

7. SMOOTH ER ROUGHER Nuclearenvelope Ribosomes SMOOTH ER ROUGH ER Figure 4.9

8. 4.10 The Golgi apparatus finishes, sorts, and ships cell products • The Golgi apparatus consists of stacks of membranous sacs • These receive and modify ER products, then send them on to other organelles or to the cell membrane

9. The Golgi apparatus Golgi apparatus Golgiapparatus “Receiving” side ofGolgi apparatus Transportvesiclefrom ER Newvesicleforming “Shipping”side of Golgiapparatus Transport vesiclefrom the Golgi Figure 4.10

10. 4.11 Lysosomes digest the cell’s food and wastes • Lysosomes are sacs of digestive enzymes budded off the Golgi LYSOSOME Nucleus Figure 4.11A

11. digest food • destroy bacteria • recycle damaged organelles • function in embryonic development in animals • Lysosomal enzymes

12. Rough ER Transport vesicle(containing inactivehydrolytic enzymes) Plasmamembrane Golgiapparatus Engulfmentof particle Lysosomeengulfingdamagedorganelle “Food” LYSOSOMES Digestion Foodvacuole Figure 4.11B

13. 4.12 Connection: Abnormal lysosomes can cause fatal diseases • Lysosomal storage diseases are hereditary • They interfere with other cellular functions • Examples: Pompe’s disease, Tay-Sachs disease

14. 4.13 Vacuoles function in the general maintenance of the cell • Plant cells contain a large central vacuole • The vacuole has lysosomal and storage functions Centralvacuole Nucleus Figure 4.13A

15. Nucleus Contractilevacuoles • These pump out excess water • Protists may have contractile vacuoles Figure 4.13B

16. 4.14 A review of the endomembrane system • The various organelles of the endomembrane system are interconnected structurally and functionally Transport vesiclefrom Golgi Transport vesiclefrom ER Rough ER Plasmamembrane Vacuole Nucleus Lysosome Golgiapparatus Smooth ER Nuclearenvelope Figure 4.14

17. ENERGY-CONVERTING ORGANELLES 4.15 Chloroplasts convert solar energy to chemical energy • Chloroplasts are found in plants and some protists • Chloroplasts convert solar energy to chemical energy in sugars Chloroplast Stroma Inner and outer membranes Granum Intermembranespace Figure 4.15

18. 4.16 Mitochondria harvest chemical energy from food • Mitochondria carry out cellular respiration • This process uses the chemical energy in food to make ATP for cellular work

19. MITOCHONDRION Outermembrane Intermembranespace Innermembrane Cristae Matrix Figure 4.16

20. THE CYTOSKELETON AND RELATED STRUCTURES 4.17 The cell’s internal skeleton helps organize its structure and activities • A network of protein fibers makes up the cytoskeleton Figure 4.17A

21. Intermediate filaments reinforce the cell and anchor certain organelles • Microtubules • give the cell rigidity • provide anchors for organelles • act as tracks for organelle movement • Microfilaments of actin enable cells to change shape and move

22. Tubulinsubunit Actin subunit Fibrous subunits 25 nm 7 nm 10 nm MICROFILAMENT INTERMEDIATEFILAMENT MICROTUBULE Figure 4.17B

23. 4.18 Cilia and flagella move when microtubules bend • Eukaryotic cilia and flagella are locomotor appendages that protrude from certain cells • A cilia or flagellum is composed of a core of microtubules wrapped in an extension of the plasma membrane

24. FLAGELLUM Electron micrograph of sections: Outer microtubule doublet Plasmamembrane Flagellum Centralmicrotubules Outer microtubule doublet Plasmamembrane Basal body Basal body(structurally identical to centriole) Figure 4.18A

25. Microtubule doublet • Clusters of microtubules drive the whipping action of these organelles Slidingforce Dynein arm Figure 4.18B

26. EUKARYOTIC CELL SURFACES AND JUNCTIONS 4.19 Cell surfaces protect, support, and join cells • Cells interact with their environments and each other via their surfaces • Plant cells are supported by rigid cell walls made largely of cellulose • They connect by plasmodesmata, channels that allow them to share water, food, and chemical messages

27. Walls of two adjacent plant cells Vacuole PLASMODESMATA Layers of one plant cell wall Cytoplasm Plasma membrane Figure 4.19A

28. Animal cells are embedded in an extracellular matrix • It is a sticky layer of glycoproteins • It binds cells together in tissues • It can also have protective and supportive functions

29. Anchoring junctions link animal cells • Communicating junctions allow substances to flow from cell to cell • Tight junctions can bind cells together into leakproof sheets TIGHTJUNCTION ANCHORING JUNCTION COMMUNICATING JUNCTION Plasma membranes ofadjacent cells Extracellularmatrix Figure 4.19B

30. 4.20 Eukaryotic organelles comprise four functional categories • Eukaryotic organelles fall into four functional groups Table 4.20

31. Table 4.20 (continued)

32. 4.21 Connection: Extraterrestrial life-forms may share features with life on Earth • It is almost certain that Earth is the only life-bearing planet in our solar system • But it is conceivable that conditions on some of the moons of the outer planets or on planets in other solar systems have allowed the evolution of life Figure 4.21