Chapter 4: Cellular Form and Function

1. Development of the cell theory: Hooke in 1663, observed cork (plant): named the cell Schwann in 1800’s states: all animals are made of cells Pasteur’s work with bacteria ~ 1860 disproved idea of spontaneous generation (living things from nonliving) Modern cell theory emerged by 1900 Chapter 4: Cellular Form and Function

2. Modern Cell Theory All organisms composed of cells and cell products. A cell is the simplest structural and functional unit of life. There are no smaller subdivisions of a cell or organism that, in themselves, are alive. An organism’s structure and all of its functions are ultimately due to the activities of its cells. Cells come only from preexisting cells, not from nonliving matter. All life, therefore, traces its ancestry to the same original cells. Because of this common ancestry, the cells of all species have many fundamental similarities in their chemical composition and metabolic mechanisms.

3. Cell Shapes thin, flat, angular contours

4. Cell Shapes 2 squarish

5. Epithelial Cell Surfaces Epithelial cells line organ surfaces Basal surface cell rests on this lower surface Lateral surface the sides of the cell Apical surface exposed upper surface

6. Cell Size Human cell size most range from 10 - 15 µm egg cells (very large)100 µm diameter, visible to naked eye nerve cell over 1 meter, muscle cell up to 30 cm, (too slender to be seen) Limitations on cell size as cell enlarges, volume increases faster than surface area so the need for increased nutrients and waste removal exceeds ability of membrane surface to exchange

7. Cell Surface Area and Volume

8. Evolving Perspective on Cells Early study with light microscope revealed surface membrane, nucleus and cytoplasm Electron microscopes have much higher resolution and revealed much greater details, such as the cell ultrastructure of the cytoplasm fibers, passageways and compartments, and organelles surrounded by cytosol (a clear gelatinous component also called intracellular fluid)

9. Cell Structure

10. Cell Structure 2

11. Defines cell boundaries Controls interactions with other cells Controls passage of materials in and out of cell Appears as pair of dark parallel lines around cell (viewed with the electron microscope) intracellular face - side faces cytoplasm extracellular face - side faces outwards Structure described by fluid-mosaic theory arrangement of mobile globular proteins embedded in an oily film of phospholipids Plasma Membrane

12. Plasma Membrane Preview

13. Membrane Lipids Lipids constitute 90 to 99% of the plasma membrane Glycolipids 5% of the lipids, found only on extracellular face, contribute to glycocalyx

14. Cholesterol 20% of the lipids, affects membrane fluidity (low conc.. more rigid, high conc.. more fluid) Phospholipid bilayer 75% of the lipids, with hydrophilic heads (phosphate) on each side and hydrophobic tails in the center motion of these molecules creates membrane fluidity, an important quality that allows self repair Membrane Lipids 2

15. Membrane Proteins Proteins constitute only 1 to 10% of the plasma membrane, but they are larger and account for half its weight Integral (transmembrane) proteins pass through membrane, have hydrophobic regions embedded in phospholipid bilayer and hydrophilic regions extending into intra- and extracellular fluids most are glycoproteins, conjugated with oligosaccharides on the extracellular side of membrane

16. Integral proteins (cont.) may cross the plasma membrane once or multiple times Peripheral proteins adhere to intracellular surface of membrane anchors integral proteins to cytoskeleton Membrane Proteins 2

17. Membrane Protein Functions Receptors Second messenger systems Enzymes Channel proteins Carriers and pumps Motor molecules Cell-identity markers Cell-adhesion molecules

18. Protein Functions - Receptors Cells communicate with chemical signals that cannot enter target cells Receptors bind these messengers (hormones, neurotransmitters) Each receptor is usually specific for one messenger

19. Second Messenger System A messenger (epinephrine) binds to a receptor 1 Receptor releases a G protein 2 G protein binds to an enzyme, adenylate cyclase, which converts ATP to cAMP, the 2nd messenger 3 cAMP activates a kinase 4 Kinases add Pi, activates or inactivates other enzymes

20. Enzymes in Plasma Membrane Break down chemical messengers to stop their effects Final stages of starch and protein digestion in small intestine Involved in producing second messengers (cAMP)

21. Protein Functions - Channel Proteins Formed by integral proteins Channels are constantly open, allow water and hydrophilic solutes in and out

22. Gates open to three type of stimulants ligand-regulated gates: bind to chemical messenger voltage-regulated gates: potential changes across plasma membrane mechanically regulated gates:physical stress such as stretch and pressure Gates control passage of electrolytes so are important in nerve signals and muscle contraction Protein Functions - Channel Proteins 2

23. Protein Functions - Motor Molecules A filamentous protein that arises deep in the cytoplasm and pulls on membrane proteins causing movement: within a cell (organelles) of a cell (WBC’s) shape of cell (cell division, phagocytosis)

24. Protein Functions - Carriers Integral proteins that bind to solutes and transfer them across membrane Carriers that consume ATP are called pumps

25. Protein Functions - Cell-identity Markers Glycoproteins contribute to the glycocalyx, a surface coating that acts as a cell’s identity tag

26. Protein Functions - Cell-adhesion Molecules Membrane proteins that adhere cells together and to extracellular material

27. Glycocalyx Surface of animal cells CHO moieties of membrane glycoproteins and glycolipids that retains a film of water

28. Structure extensions of plasma membrane (1-2?m) that increase surface area for absorptive cells (by 15- 40x in intestine, kidney) Brush border on some cells, they are very dense and appear as a fringe on apical cell surface Milking action protein filaments (actin) attach from the tip of microvillus to its base, anchors to a protein mesh in the cytoplasm called the terminal web and can shorten pushing absorbed contents into cell Microvilli

29. Cross Section of a Microvillus

30. Cilia Hairlike processes 7-10?m long, 50-200 on cell surface move mucus, egg cells Covered by saline layer created by chloride pumps Cilia beat in waves, sequential power strokes followed by recovery strokes

31. Cross Section of a Cilium

32. Cilia 2 Axoneme has a 9+2 structure of microtubules 2 central microtubules stop at cell surface 9 pairs of peripheral microtubules continue into cell as a basal body that acts as an anchor dynein (motor protein) arms on one pair of peripheral microtubules crawls up adjacent pair bending cilia Sensory cells some cilia lose motility and are involved in vision, smell, hearing and balance

33. Cilium At Cell Surface

34. Flagella Long whiplike structure that has an axoneme identical to that of a cilium Only functional flagellum in humans is the tail of the sperm

35. Nucleus Largest organelle Nuclear envelope surrounds nucleus with two unit membranes Contains DNA, the genetic program for a cell’s structure and function

36. Cell Structure

37. Rough ER extensive sheets of parallel unit membranes with cisternae between them and covered with ribosomes, continuous with nuclear envelope function in protein synthesis and production of cell membranes Smooth ER lack ribosomes, cisternae more tubular and branch more extensively, continuous with rough ER function in lipid synthesis, detoxification, calcium storage Endoplasmic Reticulum

38. Endoplasmic Reticulum Diagram

39. Ribosomes Small dark granules of protein and RNA free in cytosol or on surface of rough ER Interpret the genetic code and synthesize polypeptides

40. Golgi Complex Synthesizes CHO’s, processes proteins from RER and packages them into golgi vesicles Golgi vesicles irregular sacs near golgi complex that bud off cisternae some become lysosomes, some fuse with plasma membrane and some become secretory vesicles Secretory vesicles store a cell product for later release

41. Lysosomes Package of enzymes in a single unit membrane, variable in shape Functions intracellular digestion - hydrolyze proteins, nucleic acids, complex carbohydrates, phospholipids and other substrates autophagy - the digestion of worn out organelles and mitochondrion autolysis - programmed cell death glucose mobilization - lysosomes in liver cells break down glycogen

42. Peroxisomes Appear similar to lysosomes, lighter in color Abundant in liver and kidney Function neutralize free radicals produce H2O2 in process of alcohol detoxification and killing bacteria break down excess H2O2 with the enzyme catalase break down fatty acids into acetyl groups

43. Mitochondrion Double unit membrane Inner membrane contains folds called cristae ATP synthesized by enzymes on cristae from energy extracted from organic compounds Space between cristae called the matrix contains ribosomes and small, circular DNA (mitochondrial DNA) Reproduce independently of cell and live for 10 days

44. Mitochondrion, Electron Micrograph

45. Centrioles Short cylindrical assembly of microtubules, arranged in nine groups of three microtubules each Two centrioles, perpendicular to each other, lie near the nucleus in an area called the centrosome these play a role in cell division Other single centrioles migrate to plasma membrane forming basal bodies of cilia or flagella two microtubules of each triplet elongate to form the nine pairs of peripheral microtubules of the axoneme

46. Perpendicular Centrioles Diagram

47. Cytoskeleton Microfilaments made of protein actin, form network on cytoplasmic side of plasma membrane called the membrane skeleton supports phospholipids of p.m., supports microvilli and produces cell movement, and with myosin causes muscle contraction Intermediate fibers in junctions that hold epithelial cells together and resist stresses on a cell Microtubules

48. Microtubules Cylinder of 13 parallel strands called protofilaments (a long chain of globular protein called tubulin) Hold organelles in place and maintain cell shape Form tracks to guide organelles and molecules to specific destinations in a cell Form axonemes of cilia and flagella, centrioles, basal bodies and mitotic spindle Not all are permanent structures and can be disassembled and reassembled where needed

49. Microtubule Diagram

50. Cytoskeleton Diagram

51. Inclusions Highly variable appearance, no unit membrane Stored cellular products glycogen granules, pigments and fat droplets Foreign bodies dust particles, viruses and intracellular bacteria

52. Membrane Transport: Selective Permeability Plasma membrane allows passage of some things between cytoplasm and ECF but not others Passive transport requires no ATP, movement of particles across selectively permeable membrane, down concentration gradient filtration and simple diffusion Active transport requires ATP, transports particles up concentration gradient carrier mediated (facilitated diffusion and active transport) and bulk transport

53. Membrane Transport: Filtration Movement of particles through a selectively permeable membrane by hydrostatic pressure Hydrostatic pressure - the force exerted on the membrane by water In capillaries, blood pressure forces water, salts, nutrients and solutes into tissue fluid, while larger particles like blood cells and protein are held back

54. Simple Diffusion Simple diffusion is the movement of particles as a result of their constant, random motion Net diffusion is the movement of particles from an area of high concentration to an area of low concentration (down or with the concentration gradient)

55. Diffusion Rates Factors that affect rate of diffusion through a membrane Temperature - ? temp., ? motion of particles Molecular weight - larger molecules move slower Steepness of conc.gradient - ?difference, ? rate Membrane surface area - ? area, ? rate Membrane permeability - ? permeability, ? rate

56. Osmosis Net diffusion of water through a selectively permeable membrane from an area of more water, side B (less dissolved solute) to an area of less water, side A (more dissolved solute)

57. Osmotic Pressure Osmosis opposed by filtration of water back across membrane due to ? hydrostatic pressure Amount of hydrostatic pressure required to stop osmosis is called osmotic pressure

58. Osmolarity One osmole is 1 mole of dissolved particles 1M NaCl contains 1 mole Na+ ions and 1 mole Cl- ions/L, both affect osmosis, thus 1M NaCl = 2 osm/L Osmolarity = # osmoles/liter solution

59. Tonicity Tonicity - ability of a solution to affect fluid volume and pressure within a cell depends on concentration and permeability of solute Hypotonic solution has low concentration of nonpermeating solutes (high water concentration) cells in this solution would absorb water, swell and may burst (lyse) Hypertonic solution has high concentration of nonpermeating solutes (low water concentration) cells in this solution would lose water +shrivel (crenate)

60. Membrane Transport: Carrier Mediated Transport Proteins in cell membrane carry solutes through it Specificity solute binds to a receptor site on carrier protein that is specific for that solute Two types of carrier mediated transport are facilitated diffusion and active transport Exhibits saturation (see next slide)

61. Carrier Saturation As concentration of solute ?, rate of transport ? up to the point when all carriers are occupied and rate of transport levels off at the transport maximum

62. Membrane Transport: Facilitated Diffusion Passive transport of solute down its concentration gradient, across membrane, with aid of a carrier Solute binds to carrier, carrier changes shape and releases solute on other side of membrane

63. Active Transport Active transport of solute up its concentration gradient, across membrane, carrier requires ATP Carrier binds to ligand ATP phosphorylates carrier Carrier changes conformation Carrier releases ligand on other side Prominent example is the sodium-potassium pump

64. Sodium-Potassium Pump 3Na+ bind to receptor, carrier phosphorylated, changes conformation, releases Na+ in ECF, binds 2K+, releases Pi, resumes conformation, releases K+

65. Functions of Sodium-Potassium Pump Regulation of cell volume cell swelling stimulates the Na+- K+ pump: ? ion concentration, ? osmolarity and cell swelling Heat production Maintenance of a membrane potential Na+- K+ pump keeps inside of membrane negative, outside of membrane positive Secondary active transport transport of solute particles by carrier that does not need ATP, but depends on the concentration gradient provided by active transport pumps ...

66. Secondary Active Transport Transport of glucose by facilitated diffusion, along with Na+ by SGLT carrier (no ATP), depends on Na+- K+ pump (uses ATP)

67. Cotransport When carrier transports 2 different solutes simultaneously, or within one transport cycle Symport - a carrier that transports both solutes in the same direction Antiport - a carrier that transports solutes in opposite directions

68. Bulk Transport Transport of large particles and fluid droplets through membrane, using vacuoles or vesicles of plasma membrane, uses ATP Endocytosis - bulk transport into cell Exocytosis - bulk transport out of cell Endocytosis has three forms phagocytosis- engulfing large particles by pseudopods fluid phase pinocytosis receptor mediated endocytosis

69. Phagocytosis

70. Fluid-phase Pinocytosis Cell takes in droplets of ECF Plasma membrane dimples, then pinches off as pinocytotic vesicle Occurs in all human cells

71. Receptor Mediated Endocytosis Receptors on membrane bind to specific molecules in ECF, cluster together, then sink in, become coated with a peripheral protein, clathrin, and pinch off into cell as clathrin-coated vesicle This occurs in the uptake of LDL’s by endothelium of blood vessels Transcytosis uses this process to move a substance across a cell insulin absorbed into endothelial cell from blood by RME, then transported out into tissues

72. Receptor Mediated Endocytosis

73. Receptor Mediated Endocytosis EM

74. Exocytosis Eliminating or secreting material from cell and replacement of plasma membrane

75. Exocytosis EM