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1. 3 Cells: The Living Units: Part A

2. Generalized Cell • All cells have some common structures and functions • Human cells have three basic parts: • Plasma membrane—flexible outer boundary • Cytoplasm—intracellular fluid containing organelles • Nucleus—control center

3. Nuclear envelope Chromatin Nucleolus Nucleus Smooth endoplasmic reticulum Plasma membrane Mitochondrion Cytosol Lysosome Centrioles Centrosome matrix Rough endoplasmic reticulum Ribosomes Golgi apparatus Secretion being released from cell by exocytosis Cytoskeletal elements • Microtubule • Intermediate filaments Peroxisome Figure 3.2

4. Plasma Membrane • The plasma membrane separates the intracellular fluid (ICF) from extracellular fluid (ECF) • The plasma membrane is semi-permeable which means that some things can cross the membrane and some things cannot

5. Extracellular fluid Intracellular fluid Figure 3.3

6. Types of Membrane Transport • Passive Transport • No cellular energy (ATP) required • Substance moves down its concentration gradient • Active Transport • Energy (ATP) required • Substances are moved or“pumped” against their gradient

7. Passive Transport • What determines whether or not a substance can passively permeate (cross) a membrane? • Lipid solubility of substance • Size of the molecule that is passing PLAY http://www.youtube.com/watch?v=JShwXBWGMyY

8. Passive Transport • Simple diffusion • Facilitated diffusion • Osmosis

9. Passive Transport: Simple Diffusion • Small, nonpolar, hydrophobic substances diffuse directly through phospholipid bilayer

10. Extracellular fluid Lipid- soluble solutes Cytoplasm Figure 3.7a

11. Passive Transport: Facilitated Diffusion • Larger, hydrophilic molecules (glucose, amino acids, ions) use carrier proteins or channel proteins to pass through the plasma membrane

12. Hydrophilic molecules Figure 3.7b

13. Passive Transport: Osmosis • Movement of solvent (water) across a selectively permeable membrane from where it is most concentrated to where it is less concentrated • Water diffuses through plasma membranes: • Through lipid bilayer • Through channels (aquaporins)

14. Water molecules Lipid billayer Aquaporin Figure 3.7d

15. Passive Transport: Osmosis • Osmolarity: The measure of total concentration of solute particles • When solutions of different osmolarity are separated by a membrane, osmosis occurs until equilibrium is reached

16. (a) Membrane permeable to both solutes and water Solute and water molecules move down their concentration gradients in opposite directions. Both solutions have the same osmolarity: volume unchanged H2O Solute Solute (sugar) Membrane Figure 3.8a

17. (b) Membrane permeable to water, impermeable to solutes Solute molecules are prevented from moving but water moves by osmosis. Volume increases in the compartment with the higher osmolarity. Both solutions have identical osmolarity, increases on the right because only water is free to move Left compartment Right compartment H2O Solute (sugar) Membrane Figure 3.8b

18. Importance of Osmosis • When osmosis occurs, water enters or leaves a cell • A change in cell volume disrupts cell function

19. Tonicity • Defined as: The ability of a solution to cause a cell to shrink or swell • Isotonic: A solution that does not cause a change in cell volume • Hypertonic: A solution that causes a cell to shrink • Hypotonic: A solution that causes a cell to swell.

20. (a) Isotonic solutions (b) Hypertonic solutions (c) Hypotonic solutions Figure 3.9

21. Active Transport • The Sodium-potassium pump (Na+-K+ ATPase) is a specific example of active transport • Located in all plasma membranes • Maintains electrochemical gradients essential for functions of muscle and nerve tissues

22. Vesicular Transport • Transports large particles, macromolecules, & fluids across plasma membranes • Is active transport = requires energy ATP • Examples: • Exocytosis—moves substances out of cell • Endocytosis—moves substances into cell

23. ECF Cytoplasm Transportvesicle Endosome Lysosome (a)

24. Other Organelles • Membranous structures • Nucleus with chromatin- • Mitochondria – • Endoplasmic Reticulum (ER) (rough and smooth) – • Golgi Apparatus- • Lysosomes-

25. Nuclear envelope Nucleus Smooth ER Rough ER Vesicle Golgi apparatus Plasma membrane Transport vesicle Lysosome Figure 3.22

26. Smooth ER Nuclear envelope Rough ER Ribosomes Figure 3.18a

27. Rough ER Phagosome ER membrane Plasma mem- brane Vesicle becomes lysosome Secretory vesicle Golgi apparatus Secretion by exocytosis Extracellular fluid Figure 3.20

28. Mitochondria • Organelle with shelflike folds called cristae • Provide most of cell’s ATP (enzymes for this process are located on cristae)

29. Other Organelles • Non-Membranous structures • Centrioles- involved in cell division • Cytoskeleton- includes microfilaments, intermediate filaments and microtubules

30. Centrosome matrix Centrioles (a) Microtubules Figure 3.25a

31. Microfilaments (a) Microfilaments • Function in cell motility and aid in cell shape

32. Intermediate Filaments (b) Intermediate filaments • Resist pulling forces on the cell and attach to desmosomes

33. Microtubules (c) Microtubules • Most radiate from centrosome • Determine overall shape of cell and distribution of organelles

34. Extensions of the plasma membrane • Cilia are: short, hairlike structures that move substances across cell surfaces • Flagella are: Whiplike, tails that move entire cell • Microvilli are: fingerlike extensions found on absorptive cells

35. Power, or propulsive, stroke Recovery stroke, when cilium is returning to its initial position 1 2 3 4 5 6 7 (a) Phases of ciliary motion. Layer of mucus Cell surface (b) Traveling wave created by the activity ofmany cilia acting together propels mucusacross cell surfaces. Figure 3.27

36. Microvillus Actin filaments Terminal web Figure 3.28

37. The Cell Cycle • Includes: • Interphase • Period from cell formation to cell division • Three sub phases of Interphase: • G1 (gap 1)—growth and metabolism • S (synthetic)—DNA replication • G2 (gap 2)—preparation for division • Cell division (mitotic phase)

38. S Growth and DNA synthesis G2 Growth and final preparations for division G1 Growth M Figure 3.31

39. DNA Replication • Helicase untwists the double helix and exposes complementary chains • Each nucleotide strand serves as a template for building a new complementary strand • DNA polymerase forms new DNA strand

40. DNA Replication • End result: two DNA molecules formed from the original • This process is called semiconservative replication

41. Template for synthesis of new strand DNA polymerase Free nucleotides Chromosome Leading strand Lleading and lagging strands are synthesized in opposite directions Lagging strand Old DNA Helicase unwinds the double helix and Exposes bases Replication fork Adenine Thymine Cytosine DNA polymerase Old (template) strand Guanine Figure 3.32

42. Cell Division • Mitotic (M) phase of the cell cycle • Essential for body growth and tissue repair • Does not occur in most mature cells of nervous tissue, skeletal and cardiac muscle

43. Cell Division • Includes two distinct events: • Mitosis—four stages of nuclear division: • Prophase • Metaphase • Anaphase • Telophase • Cytokinesis—division of cytoplasm by cleavage furrow

44. S Growth and DNA synthesis G2 Growth G1 Growth M Figure 3.31

45. Prophase • Chromosomes condense and become visible • Mitotic spindle form • Nuclear envelope fragments

46. Early mitotic spindle Early Prophase Aster Chromosome consisting of two sister chromatids Centromere Early Prophase Figure 3.33

47. Microtubule Fragments of nuclear envelope Late Prophase Microtubule Late Prophase Figure 3.33

48. Metaphase • Chromosomes are aligned at the equator • Metaphase plate = The plane midway between the poles of the cell

49. Metaphase Spindle Metaphase plate Metaphase Figure 3.33

50. Anaphase • Shortest phase • Chromosomes are pulled to opposite poles by microtubules