Cell Structure and Function

1. Cell Structure and Function

2. Cells • Smallest living unit • Most are microscopic

3. Discovery of Cells • Robert Hooke (mid-1600s) • Observed sliver of cork • Saw “row of empty boxes” • Coined the term cell

4. Cell theory • (1839)Theodor Schwann & Matthias Schleiden “ all living things are made of cells” • (50 yrs. later) Rudolf Virchow “all cells come from cells”

5. Principles of Cell Theory • All living things are made of cells • Smallest living unit of structure and function of all organisms is the cell • All cells arise from preexisting cells (this principle discarded the idea of spontaneous generation)

6. Cell Size

7. Cells Have Large Surface Area-to-Volume Ratio

8. Characteristics of All Cells • A surrounding membrane • Protoplasm – cell contents in thick fluid • Organelles – structures for cell function • Control center with DNA

9. Cell Types • Prokaryotic • Eukaryotic

10. Prokaryotic Cells • First cell type on earth • Cell type of Bacteria and Archaea

11. Prokaryotic Cells • No membrane bound nucleus • Nucleoid = region of DNA concentration • Organelles not bound by membranes

12. Eukaryotic Cells • Nucleus bound by membrane • Include fungi, protists, plant, and animal cells • Possess many organelles Protozoan

13. Representative Animal Cell

14. Representative Plant Cell

15. Organelles • Cellular machinery • Two general kinds • Derived from membranes • Bacteria-like organelles

16. Bacteria-Like Organelles • Derived from symbiotic bacteria • Ancient association • Endosymbiotic theory • Evolution of modern cells from cells & symbiotic bacteria

17. Plasma Membrane • Contains cell contents • Double layer of phospholipids & proteins

18. Phospholipids • Polar • Hydrophylic head • Hydrophobic tail • Interacts with water

19. Movement Across the Plasma Membrane • A few molecules move freely • Water, Carbon dioxide, Ammonia, Oxygen • Carrier proteins transport some molecules • Proteins embedded in lipid bilayer • Fluid mosaic model – describes fluid nature of a lipid bilayer with proteins

21. Membrane Proteins 1. Channels or transporters • Move molecules in one direction 2. Receptors • Recognize certain chemicals

22. Membrane Proteins 3. Glycoproteins • Identify cell type 4. Enzymes • Catalyze production of substances

23. Cell Walls • Found in plants, fungi, & many protists • Surrounds plasma membrane

24. Cell Wall Differences • Plants – mostly cellulose • Fungi – contain chitin

25. Cytoplasm • Viscous fluid containing organelles • components of cytoplasm • Interconnected filaments & fibers • Fluid = cytosol • Organelles (not nucleus) • storage substances

26. Cytoskeleton • Filaments & fibers • Made of 3 fiber types • Microfilaments • Microtubules • Intermediate filaments • 3 functions: • mechanical support • anchor organelles • help move substances

27. A = actin, IF = intermediate filament, MT = microtubule

28. Cilia & Flagella • Provide motility • Cilia • Short • Used to move substances outside human cells • Flagella • Whip-like extensions • Found on sperm cells • Basal bodies like centrioles

29. Cilia & Flagella Structure • Bundles of microtubules • With plasma membrane

31. microtubules are the thickest filaments of the cytoskeleton • hollow, rod -shaped cylinders about 25 nm in diameter • made of a-tubulin and b-tubulin dimers • dimers can be added or removed from either end (dynamic nature) • one end (plus end) adds dimers more rapidly than the minus end • can be anchored, where an end is attached to something and can no longer add or lose dimers

32. microtubule-organizing centers (MTOCs) serve as anchors • centrosome in animal cells • centrosome has two centrioles in a perpendicular arrangement • centrioles have a 9x3 structure: 9 sets of 3 attached microtubules forming a hollow cylinder • used for assembly of microtubules for use throughout the cell

33. microtubule-organizing centers (MTOCs) serve as anchors • centrioles are duplicated before cell division • play an organizing role for microtubule spindles in cell division • other eukaryotes must use some alternative MTOC during cell division; still incompletely described

34. microtubules are involved in moving organelles • motor proteins (such as kinesin or dynein) attach to organelle and to microtubule • using ATP as an energy source, the motor proteins change shape and thus produce movement • microtubule essentially acts as a track for the motor protein • motor proteins are directional; kinesin moves toward the plus end, dynein away from it

35. cilia and flagella are made of microtubules • thin, flexible projections from cells • used in cell movement, or to move things along the cell surface • share the same basic structure; called cilia if short (2-10 mm typically) and flagella if long (typically 200 mm) • central stalk covered by cell membrane extension, and anchored to a basal body • 9x3 structure • stalk has two inner microtubules surrounded by nine attached pairs of microtubules • 9+2 arrangement

36. cilia and flagella are made of microtubules • stalk has two inner microtubules surrounded by nine attached pairs of microtubules • 9+2 arrangement • dynein attached to the outer pairs actually fastens the pair to its neighboring pair • dynein motor function causes relative sliding of filaments; this produces bending movement of the cilium or flagellum

37. microfilaments are solid filaments about 7 nm in diameter • composed of two entwined chains of actin monomers • linker proteins cross-link the actin chains with each other and other actin associated proteins • actin monomers can be added to lengthen the microfilament or removed to shorten it; this can be used to generate movement

38. microfilaments are solid filaments about 7 nm in diameter • important in muscle cells; in conjunction with myosin, they are responsible for muscle contraction • used for many cell movements such as: • contractile structures • forming cell extensions • “pinching in” during cell division

39. intermediate filaments • typically just a bit wider than microfilaments, this is the catch-all group for cytoskeletal filaments composed of a variety of other proteins • the types of proteins involved differ depending on cell types and on the organism; apparently limited to animal cells and protozoans

40. intermediate filaments • not easily disassembled, thus more permanent • a web of intermediate filaments reinforces cell shape and positions of organelles (they give structural stability) • prominent in cells that withstand mechanical stress • form the most insoluble part of the cell

41. What are the functions of the cytoskeleton? • What are the three main types of cytoskeleton? Describe the structure and function(s) of each type.

42. Describe the structure and function(s) of: • motor proteins • MTOCs • centrosomes • centrioles • cilia and flagella

43. Centrioles • Pairs of microtubular structures • Play a role in cell division

44. Membranous Organelles • Functional components within cytoplasm • Bound by membranes

45. Nucleus • Control center of cell • Double membrane • Contains • Chromosomes • Nucleolus

46. Nuclear Envelope • Separates nucleus from rest of cell • Double membrane • Has pores

47. DNA • Hereditary material • Chromosomes • DNA • Protiens • Form for cell division • Chromatin

48. Nucleolus • Most cells have 2 or more • Directs synthesis of RNA • Forms ribosomes

49. Endoplasmic Reticulum • Helps move substances within cells • Network of interconnected membranes • Two types • Rough endoplasmic reticulum • Smooth endoplasmic reticulum

50. Rough Endoplasmic Reticulum • Ribosomes attached to surface • Manufacture protiens • Not all ribosomes attached to rough ER • May modify proteins from ribosomes