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CHAPTER 4 A Tour of the Cell

CHAPTER 4 A Tour of the Cell. Modules 4.6 – 4.14. The nucleus is the cell’s genetic control center. The largest organelle is usually the nucleus (5um in diameter. Most cells have one nucleus but others may have multiple or lobed nuclei

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CHAPTER 4 A Tour of the Cell

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

  2. The nucleus is the cell’s genetic control center • The largest organelle is usually the nucleus (5um in diameter. • Most cells have one nucleus but others may have multiple or lobed nuclei • The nucleus is separated from the cytoplasm by the nuclear envelope. The envelope is a double lipid bilayer membrane with nuclear pores (100nm diameter). • The nucleus is the cellular control center • It contains the DNA that directs the cell’s activities • It contains a nucleolus region for the synthesis of ribosomal subunits

  3. The Nuclear Lamina

  4. Cells with multiple nuclei Some muscle cells and megakaryocytes

  5. The Phospholipid

  6. The membranes of the cell A selectively permeable, dynamic membrane 7.5-10nm thick. The Fluid Mosaic Model. Movement 2um/sec.

  7. 4.7 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 • The ER or endoplasmic reticulum (“network”) is part of the endomembrane system and accounts for greater than ½ of all membranes.

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

  9. 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 includes the ribosomes. • Ribosomes on it’s surface produce proteins. • Provides a large surface area for reactions. • Many of the proteins to be exported out of the cell are made here. Figure 4.8

  10. 4.9 Smooth endoplasmic reticulum has a variety of functions • Smooth ER synthesizes lipids. Enzymes for synthesis in the membrane. • In some cells, like liver cells, it regulates carbohydrate metabolism by removing a phosphate from glucose phosphate and allowing the glucose to enter the blood. • In liver it also helps to break down toxins and drugs by adding a hydroxyl group to help solubilize them in water so that they can be excreted. • In muscle the ER stores calcium against its concentration gradient until a signal allows its release and a muscle contraction ensues.

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

  12. 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 in vessicles • The cis side of the golgi faces the ER while the trans faces the outer membrane • Discovered by Emilio Golgi in 1898.

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

  14. 4.11 Lysosomes digest the cell’s food and wastes • Lysosomes are sacs of digestive enzymes budded off the Golgi • Because they are separate compartments, digestive enzymes can be stored that function at different pH’s. The compartment protects the rest of the cell from degredation by these enzymes. LYSOSOME Nucleus Figure 4.11A

  15. digest food • destroy bacteria • recycle damaged organelles • function in embryonic development in animals. Fingers in human embryos, tails from tadpoles. • digest contents in vacuoles when the lysosome fuses with the vacuole. • Lysosomal enzymes

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

  17. 4.12 Connection: Abnormal lysosomes can cause fatal diseases • Lysosomal storage diseases are hereditary • They interfere with other cellular functions • Examples: Pompe’s disease (cells lack alpha glucosidase) causes a build up of glycogen in tissues especially heart and other muscles, Tay-Sachs disease (ganglioside GM2 build up in tissues and nerve cells in the brain) cells lack Hexosaminidase A.

  18. 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 • It may take up nearly 90% of the cell’s space Centralvacuole Nucleus Figure 4.13A

  19. Nucleus Contractilevacuoles • These pump out excess water • Paramecium with contractile vacuole • Protists may have contractile vacuoles Figure 4.13B

  20. 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

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