Unit 2: Cell Biology

1. Unit 2: Cell Biology Outcomes A and G Chapters 3, 4, and parts of 7 Prepared by: Wendy VermillionColumbus State Community College Reformatted for use at G.P. Vanier by Ilene Yeomans

2. A. Cellular Level of Organization 1. Cells are the smallest unit of life • Exhibit all characteristics of life • Are highly organized • Many become specialized for complex functions 2. Cell theory • All living things are composed of cells • Cells are the functional and structural units of organisms • All cells are derived from previously existing cells 3. Discovery of cells a) Antonie van Leeuwenhoek- invented the light microscope b) Robert Hooke- first observed cells in cork (actually saw the cell walls of dead cells) c) Schleiden and Schwann-proposed cell theory

3. Cellular level of organization, cont’d. 4. Cell size • Most cells are smaller than 1 mm in diameter • Surface area/volume ratio determines cell size:

4. Cell Size, cont’d.determining surface area to volume ratios Let L be the length of one side = L x L x 6 = L x L x L 6 1 6 6:1 24 8 3 3:1 216 216 1 1:1

5. Cell Size continued • As the cell size increases, the volume increases faster than the surface area does • Therefore small cells have a greater surface area to volume ratio than larger cells • Nutrients from the environment must cross the surface of the cell to enter • Cells must be small in order for the surface area to be adequate to supply nutrients • This is one reason why we are made up of lots of cells instead of just one big one

6. Cellular level of organization, cont’d.

7. B. Eukaryotic cells • Eukaryotic cells have a membrane-bound nucleus • Cell Membrane (or Plasma Membrane)

8. Eukaryotic cells, cont’d. • Organelles • Subcellular structures which perform specific life functions for the cell • Many organelles are found in both animal and plant cells • Some are found exclusively in plants or animals • Plants • chloroplasts, large central vacuole, cell wall • Animals • centrioles

9. Animal cell anatomy • Fig. 3.2

10. Eukaryotic Cells cont’d • Nucleus • Contains the genetic material (DNA) • Nucleoplasm -semifluid within nucleus • Chromatin -threadlike DNA which has a grainy appearance • Nucleoli (Nucleolus) -dark regions of chromatin • These produce rRNA which makes up the two subunits of ribosomes when combined with protein • Nuclear membrane - double layered, surrounds nucleus and has large pores

11. The Nucleus and Nuclear Envelope • Fig 3.4

12. C. Animal Cell Organelles 1. Ribosomes- • Site of protein assembly (“Protein Synthesis”) • Composed of rRNA and protein subunits • Exist either as free ribosomes (in groups called polysomes) or bound to endoplasmic reticulum (ER) • Polysomes produce multiple copies of the same protein for use inside the cell • Proteins produced at the ER’s ribosomes are destined for export from the cell

13. Organelles, cont’d. 2. Rough endoplasmic reticulum (RER) • Complex system of sacs and channels • Has attached ribosomes • Serves as site of assembly of proteins for export • Assembled proteins enter channels for processing • e.g. addition of sugar chains to form glycoproteins • Released in vesicles 3. Smooth endoplasmic reticulum (SER) • No ribosomes • Synthesizes lipid products such as phospholipids and steroids AND is used to detoxify • Product released in vesicles

14. The Endoplasmic Reticulum • Fig 3.5

15. Organelles, cont’d. 4. Golgi Apparatus (or Golgi Body) • Packaging and processing center for cell products • Receives the vesicles from ER • Vesicles fuse with Golgi and products are released inside • Further modification of proteins occurs • Products are packaged into secretory vesicles and released to travel to the cell membrane • Golgi also produces lysosomes • Easier to remember the functions with MRS Golgi = • M (modify), R (repackage), S (sort)

16. The Endomembrane System Smooth ER Rough ER • Fig 3.6

17. Organelles, cont’d. 5. Lysosomes • Contain hydrolytic enzymes (very powerful enzymes) • Three functions of lysosomes: • Intracellular Digestion • lysosome fuses with a vesicle and digests its contents • Autodigestion • lysosomes fuse with worn out organelles or cell components and digest them (e.g. mitochondria) • Autolysis • lysosomes sometimes called “suicide sacs” because they release their enzymes into the cell causing cell death

18. The Endomembrane System • Fig 3.6

19. Organelles, cont’d. 6. Mitochondria • Site of aerobic cellular respiration = production of ATP (energy) • Uses oxygen we breathe and food that we eat to produce energy for every action in and of our body Up to38 ATP are made per glucose molecule • 6 O2 + C6H12O6 6 CO2 + 6 H2O

20. Mitochondrion Structure • Fig. 3.9

21. Organelles, cont’d…. 7. Peroxisomes • Specialized vesicles • Smaller than lysosomes • Contain powerful oxidative enzymes • Use oxygen to strip H’s from certain molecules • Produce peroxide (H2O2), hence the name • Role is detoxification • Found in large numbers in liver cells

22. Organelles, continued 8. Vaults • Serve as cellular transport vehicles (we think) • Discovered in the early 1990s (do not show up with normal staining techniques) • Shaped like octagonal barrels, hollow, 3X size of ribosomes • Intriguingly, vaults are the same size and shape as nuclear pores • Research supports vaults’ role in transport from the nucleus to the cytoplasm • Unknown cargo, BUT are the right size to accommodate the two ribosomal subunits!

23. D. Cytoskeleton • The Cytoskeleton • Maintains cell shape • Allows cells to move or allows organelles to move within cells • Made of protein • Components include microfilaments and microtubules: • Microfilamentsare slender fibers that often occur in bundles e.g. ACTIN which works to contract muscles • Microtubules protrude from the centrosome and form centrioles, cilia, and flagella

24. Eukaryotic cells, cont’d. • Centrioles see p60 • Short tubules with 9+0 pattern of microtubule triplets • In animal cells, centrosome is composed of 2 centrioles • Believed to be involved in microtubule formation including mitotic spindle • Basal Bodies • Found at the bases of both cilia and flagella • Organize the microtubules in the cilium or flagellum • Have a 9+0 arrangement of microtubules.

25. Centrioles • Fig. 3.14

26. E. Cellular Movement • Cilia and Flagella • Cilia are generally multiple and hair-like • Move mucus (phlegm) up the trachea • Move the egg (or zygote) along the oviduct • Flagella occur single or double and are whip-like • Propel the sperm • BOTH have a 9+2 pattern of microtubules

27. Structure of Cilia and Flagella • Fig. 3.15

28. The Cell Membrane

29. F. Cell (Plasma) Membrane 1. Membrane Structure • Fluid-Mosaic Membrane Model (FMMM) • Phospholipid bilayer • Hydrophilic heads face surfaces • Hydrophobic tails face inward • Proteins • Integral proteins- embedded • Peripheral proteins- surface • Glycoproteins and Glycolipids • Cell markers (antigens) • Cholesterol • Changes fluidity of the membrane

30. Fluid-Mosaic Model of Membrane Structure • Fig. 4.1

31. Cell Membrane cont’d • Functions of the Cell Membrane • Functions as a barrier between the cell and its environment • Regulates what enters or exits the cell (Regulates transport of substances into and out of the cell) • Contains receptors that determine how a cell will respond to stimuli in the environment • Contains proteins that are important in immune responses • It is a very dynamic, fluid structure

32. membrane protein diversity • Fig 4.2

33. G. Permeability of Cell Membrane • Cell membrane is selectively permeable • Some substances pass through the membrane freely while others do not • Crossing depends on factors like: • size and shape of molecule, • molecule’s chemical nature (e.g. lipid soluble?) • temperature • number of passages (channel proteins, carrier proteins, etc.) • Rate depends on: • concentration gradient of substance • permeability of membrane to substance • surface area of membrane • molecular weight of substance • distance travelled (thickness of membrane)

34. H. Passive Movement • Passive Mechanisms (of crossing the cell membrane) = no cellular energy required • Kinetic energy drives passive mechanisms • Movement is always from high concentration to low concentration ( = DOWN a concentration gradient)

35. Passive mechanisms…. • For instance: • Diffusion • The movement of substances from an area of high concentration to an area of low concentration • Drink crystals in water • Perfume in a room • The movement of lipid-soluble substances directly through the phospholipid bilayer from an area of high concentration to an area of low concentration • Gases (oxygen and carbon dioxide) • Alcohol

36. Process of Diffusion • Fig. 4.4

37. High Low Passive mechanisms…. 2. Facilitated Transport • The movement of small, lipid-insoluble substances such as simple sugars and amino acids across a cell membrane • Uses a carrier protein • Movement is down a concentration gradient

38. Facilitated Transport • Fig. 4.8

39. Movement of Molecules Across Cell Membranes • Table 4.1

40. Passive Mechanisms Cont’d 3. Osmosis- • A special case of diffusion = movement of WATER from an area of lowsolute concentration to an area of highsolute concentration. • The water moves to an area of high ‘saltiness’ in order to dilute the area • Water moves through protein-lined pores (“aquaporins”) in the cell membrane. • Osmotic pressure- force that causes water to move in a direction

41. Tonicity • Isotonic solutions-no change • Hypotonicsolutions-cause cells to swell and burst • Hypertonicsolutions-cause cells to shrink, or crenate

42. Osmosis demonstration • Fig. 4.6

43. Osmosis in animal and plant cells • Fig 4.7

44. High Low Permeability of plasma membrane, cont’d. I. Active Mechanisms = require ATP • Active Transport • Uses ATP • Requires a carrier protein • Transports molecules from an area of low concentration to an area of high concentration = (UP or AGAINST a concentration gradient) • Example: • sodium/potassium pump in nerve cells • Iodine accumulation in the thyroid gland

45. Active Transport • Fig. 4.9

46. The Sodium-Potassium Pump • Fig 4.10

47. Active Mechanisms, cont’d. 2. Exocytosis • Requires ATP • Vesicle used • Transports cell products and wastes (big stuff) out of the cell by vesicle formation • Vesicles fuse with plasma membrane • Products are released • Vesicle membrane becomes part of the plasma membrane

48. Exocytosis • Fig 4.11

49. Active Mechanisms, cont’d 3. Endocytosis • Requires ATP • Vesicle used • Transports substances (big stuff) into the cell by vesicle formation • membrane invaginates and surrounds a substance, then pinches off to form a vesicle

50. Endocytosis, cont’d • Pinocytosis-”cell drinking” material is liquid or small • Receptor-mediated endocytosis is a specific type of pinocytosis which occurs in response to receptor stimulation b) Phagocytosis-”cell eating” material taken in is large like bacteria or cell debris