Cell Structure and Function

1. Cell Structure and Function Biology 155 Russo-Neustdt

2. I. Definition of a cell: • basic structural and functional units of life • the smallest units that display the characteristics of life, i.e. reproduction, metabolism, response to stimuli

3. II. Cell Structure Detail Fig 4.4A

4. III. General Subdivisions of a Cell A. Nucleus (regulatory center of the cell) B. Plasma Membrane (selectively permeable boundary between the cell and the environ-ment) C. Cytoplasm (everything between the plasma membrane and the nuclear compartment) Fig. 4.4A Organelles are individual compartments in the cytoplasm

5. (A. Phospholipid bilayer with nuclear pores = membrane barrier to control what enters/leaves nucleus) IV. The Nucleus Fig 4.6 (D. Ribosome synthesis) A D B. (B. Proteins embedded in the nuclear envelope; most substances must pass through the pores to enter or leave the nucleus) C (C. chromosomes with DNA that regulate all cell activities)

6. V. Plasma Membrane Fig. 4.5B +5.1A • Structure = phospholipd bilayer with proteins embedded in and attached to the inner (intracellular) and outer (extracellular) surfaces

7. V. Plasma Membrane Fig. 4.5b + 5.1A Most substances must use proteins to gain access to cell; proteins are selective Lipids move freely through bilayer B. Function – “selectively permeable”barrier; main responsibility is to ensure that the composition of extracellular fluid is not the same as the composition of the intracellular fluid

8. V. Plasma Membrane Fig. 4.5B + 5.1A Serves as attachment site for the cytoskeleton B. Function(continued) – phospholipids are liquid at body temperature so membrane functions as a “fluid mosaic”

9. Plasma Membrane (continued) C. Glycocalyx = protein and carbohydrate coat covering the extracellular surface of the plasma membrane (part of the extracellular matrix) • Allows attachment to other cells • Allows the cell to interact with the environment

10. Plasma Membrane Most substances must use proteins to gain access to cell; proteins are selective Lipids move freely through bilayer “selectively permeable”

11. How do things move across the plasma membrane? • Passive Transport • Active Transport

12. Passive Transport • Does not require Adenosine Triphosphate or ATP (energy) • Involves diffusion across the membrane - net random movement of molecules from an area of high concentration to an area of low concentration (down the concentration gradient)

14. Facilitated

15. Glucose and water Where glucose cannot cross the membrane passively but water can

16. Active Transport • Does require ATP (energy) • net random movement of molecules from an area of low concentration to an area of high concentration (against the concentration gradient)

18. Which is passive transport? Which is active transport?

19. A. Cytoplasm = water with dissolved salts, nutrients, enzymes; site of many chemical reactions VI. Cytoplasm flagellum Cytoskeleton = network of protein fibers extending throughout the cytoplasm B. Organelles = “little organs”found throughout cytoplasm Fig. 4.4A

20. Functions of the Cytoskeleton • Provides support and structure for the cell • Very dynamic, always remodeled • Important in cellular reproduction

21. Functions of the Cytoskeleton - continued Fig. 4.18A+B • Important in cell movement • Cilia = short and numerous • Flagella = long, single • (Moveable portions of the cytoskeleton that project from the surface of the cell)

22. B. Organelles Separate compartments within the cytoplasm formed by membranes Each organelle has a specific function in the cell

23. 1. Mitochondrion (“thread granule”) Fig. 4.14 major source of ATP (adenosine triphosphate) which is the cellular energy storage molecule, requires oxygen (aerobic)

24. 2. Ribosomes = site of protein synthesis; function in the cytoplasm, but are assembled in the nucleolus a. Free = unbound in the cytoplasm; produce proteins for use inside the cell b. Bound = attached to the endoplasmic reticulum; produce proteins for export and for the plasma membrane Fig. 4.7

25. 3. The Cytomembrane System system of tubes and chambers formed by membranes, extensively distributed throughout the fluid cytoplasm, involved in synthesis, modification, processing and packaging of cellular lipids and proteins

26. a. Endoplasmic Reticulum (ER) -“within the cytoplasm network”, system of tubes and sacs formed by membranes Fig. 4.9A Smooth = without bound ribosomes, functions in lipid synthesis, carbohydrate metabolism, drug detoxification Rough = with bound ribosomes, modifies proteins produced on the ribosomes

27. b. Golgi Apparatus = seriesof flattened sacs formed by membranes, functions in final lipid and protein processing prior to use by the cell Fig. 4.10 Vesicles =small membrane bound structures that are used to transport proteins and lipids around the cell

28. Interaction of ER and Golgi Fig. 4.13

29. Next time: Tissues, Organ Systems and Homeostasis