UNIT III – CELL STRUCTURE & FUNCTION

1. UNIT III – CELL STRUCTURE & FUNCTION • Hillis – Ch 4,5 • Baby Campbell – Ch 4,5 • Big Campbell – Ch 6,7,11

2. I. DISCOVERY OF CELLS • History of Microscopes • Anton van Leeuwenhoek • Robert Hooke • Cell Theory • All living things are made of cells. • Cells are the smallest working unit. • All cells come from pre-existing cells through cell division.

3. I. DISCOVERY OF CELLS, cont. • Types of Microscopes • Compound Light Microscope • Magnification • Resolution • Advances in light microscopy include • Confocal • Fluorescent • Phase Contrast • Super-resolution • Electron Microscope • Scanning Electron Microscope (SEM) • Transmission Electron Microscope (TEM)

4. I. DISCOVERY OF CELLS, cont. • Cell Size • Metabolic needs impose both upper & lower limits on cell size • How small? • Must have enough space for DNA, enzymes • Mycoplasma sp. - < 1 μm • How large? • Surface Area to Volume Ratio • Adaptations

5. II. CELL TYPES • Prokaryotic Cells • Typically smaller than euks • Bacteria • Kingdom • Kingdom • No true nucleus – DNA found as a single chromosome in region called nucleoid

6. II. CELL TYPES, cont • Prokaryotic Cells

7. II. CELL TYPES, cont • Eukaryotic Cells • Larger, more complex • Contain true nucleus, membrane-bound organelles suspended in cytosol • Composed of • Nucleus • Ribosomes • Endomembrane System • ER • Golgi Apparatus • Lysosomes • Vacuoles • Mitochondria/Chloroplasts • Peroxisomes • Cytoskeleton

8. III. EUKARYOTIC CELL STRUCTURES _______________ Cell _____________ Cell

9. III. EUKARYOTIC CELL STRUCTURES, cont • Control center of eukaryotic cell • Double membrane that protects nucleus; continuous with ER • Contains pores • Site of ribosome production • DNA wrapped in protein

10. III. EUKARYOTIC CELL STRUCTURES, cont • Suspended in cytosol or found on rough ER • Site of protein production in a cell

11. III. EUKARYOTIC CELL STRUCTURES, cont • Endomembrane System • Endoplasmic Reticulum • Interconnected network continuous with nuclear envelope • Rough ER • Smooth ER

12. III. EUKARYOTIC CELL STRUCTURES, contEndomembrane System, cont • “Cell postmaster” • Receives transport vesicles from ER; modifies, stores, and ships products • Receiving side is known as the cisface; shipping side is known as the trans face

13. III. EUKARYOTIC CELL STRUCTURES, contEndomembrane System, cont • Sacs containing hydrolytic enzymes • Used for recycling cellular materials, destroying pathogens

14. III. EUKARYOTIC CELL STRUCTURES, contEndomembrane System, cont • Storage sac • Plants typically have large, central vacuole surrounded by membrane called tonoplast. Absorbs water and helps plant cell to grow larger • Some protists have contractile vacuole to pump out excess water

15. III. EUKARYOTIC CELL STRUCTURES, cont • Site of oxidative respiration • Contain own DNA, ribosomes • Found in virtually all euk cells • Enclosed by 2 membranes; inner membrane has folds called cristae to increase surface area

16. III. EUKARYOTIC CELL STRUCTURES, cont • Type of plastid that carries out photosynthesis by converting solar energy to chemical energy (glucose) • Contain membranous system of flattened sacs called thylakoids – stack is called a granum • Fluid surrounding thylakoids is called stroma • Contains DNA, ribosomes

17. III. EUKARYOTIC CELL STRUCTURES, contEndosymbiont Theory

18. III. EUKARYOTIC CELL STRUCTURES, cont • Membrane-bound compartments that use O2 to carry out metabolism • H2O2 is produced; broken down by _________________

19. III. EUKARYOTIC CELL STRUCTURES, cont • Provides structural support to cell • Allows for movement • Attachment site for organelles, enzymes • More extensive in animal cells • Composed of three types of proteins • Actin • More fixed • Keratin

20. III. EUKARYOTIC CELL STRUCTURES, contCytoskeleton, cont

21. IV. CELL BOUNDARIES • Cell Wall • Found in • Rigid structure; protects, maintains shape of cells • Prevents excess water uptake • Plant cell wall • Cellulose • Pectin - Sticky polysaccharide found between cell walls of adjacent cells • Plasmodesmata - Perforations between adjacent cell walls that allow for movement of materials from one cell to another

22. IV. CELL BOUNDARIES, cont • Extracellular Matrix of Animal Cells • Holds cells together, protects & supports cells • Allows for communication between cells • Composed primarily of glycoproteins – proteins with covalently-bonded carbohydrate chains attached • Must abundant glycoprotein in most animals is collagen

23. IV. CELL BOUNDARIES, cont • Intracellular Junctions in Animal Cells • Tight Junctions – Press membranes together very tightly; prevents leakage of fluid • Desmosomes (Anchoring Junctions) – Fasten cells together in sheets • Gap Junctions – Allow for movement of cytoplasm from one cell to another; important in communication between cells

24. IV. CELL BOUNDARIES, cont • Cell (Plasma) Membrane • Selectively-permeable barrier found in all cells • Composed primarily of phospholipid bilayer • Fluid Mosaic Model • “Fluid” – Not a rigid structure. Organization due to high concentration of water inside & outside cell

25. IV. CELL BOUNDARIES, cont • Organization of Plasma Membrane

26. IV. CELL BOUNDARIES, cont • Fluidity of Plasma Membrane

27. IV. CELL BOUNDARIES, cont • Cell Membrane, cont • Proteins - “Mosaic” – Assortment of different proteins embedded in bilayer; determine most of membrane’s specific functions. Act as channels, pumps, enzymes in metabolism, binding sites, etc • Integral Proteins – Embedded in phospholipid layer • Peripheral Proteins – Bound to surface of membrane

28. IV. CELL BOUNDARIES, contMembrane Proteins

29. IV. CELL BOUNDARIES, cont • Cell Membrane, cont • Carbohydrates • “ID tags” that identify cell. • Enable cells to recognize each other and foreign cells. • May be bonded to lipids (glycolipids) or proteins (glycoproteins)

30. IV. CELL BOUNDARIES, cont

31. V. CELL TRANSPORT

32. V. CELL TRANSPORT, cont • Passive Transport – Movement of materials from high to low concentration. No energy output required. • Diffusion • Random movement of a substance across membrane down concentration gradient • No net movement once equilibrium is reached

33. V. CELL TRANSPORT, cont • Passive Transport, cont • Facilitated Diffusion • Passive transport of molecules across cell membrane with the help of transport proteins • Utilized by large molecules, charged particles, polar molecules • Water

34. V. CELL TRANSPORT, cont • Passive Transport, cont • Osmosis – Diffusion of water across a membrane. Tonicity refers to tendency of cell to gain or lose water. If the solution is • Isotonic relativeto the cell – Solute concentration is same on both sides of membrane. No net movement of water. • Hypertonic relative to the cell – Concentration of solute is greater outside cell → water moves out of cell until equilibrium is reached. Cell may shrivel. • Hypotonic relativeto the cell – Concentration of solute is lower outside cell → water moves into cell until equilibrium is reached. Cell may swell to bursting point.

35. V. CELL TRANSPORT, cont • Passive Transport / Osmosis, cont • Water Potential • Used to predict the passive movement of water • Designated as Ψ • Water always moves from an area of higher water potential → lower water potential • ΨS = • ΨP =

36. V. CELL TRANSPORT, cont • Passive Transport/Osmosis, cont • Osmoregulation • Cells must have mechanism to prevent excess loss, uptake of water • Cell wall, contractile vacuole • Plasmolysis – Seen in plants; excessive water loss causes cell membrane to pull away from cell wall

37. V. CELL TRANSPORT, cont

38. V. CELL TRANSPORT, cont • Active Transport • Movement of materials against concentration gradient. Requires energy output by cell • Carrier Proteins – Na+ / K+ Pump

39. V. CELL TRANSPORT, cont • Active Transport, cont • Proton Pump

40. V. CELL TRANSPORT, cont • Active Transport, cont • Exocytosis • Secretion of biomolecules by fusion of vesicles with cell membrane. Biomolecules “spit out”. • Hormones, neurotransmitters, etc

41. V. CELL TRANSPORT, cont • Active Transport, cont • Endocytosis – “Sucking In”. Cell membrane surrounds, engulfs particle or biomolecule, pinches in to form vesicle. • Phagocytosis – “Sucking in” food particles • Pinocytosis – “Sucking in” fluid droplets • Receptor-mediated Endocytosis – Very specific

42. VI. CELL SIGNALING • Autocrine Signaling

43. VI. CELL SIGNALING, cont • Coordinates cell activities, development • Typically involves 3 steps: • Reception – Target cell’s detection of signal molecule due to binding of signal molecule to receptor protein in cell membrane • Transduction – Binding of signaling molecule changes receptor protein; triggers a sequence of events within cell • Response – Results in specific cellular response; for example, activation of genes, enzyme catalysis, etc.

44. VI. CELL SIGNALING, cont • Reception • Typically involves G Proteins

45. VI. CELL SIGNALING, cont • Transduction • Typically multi-step pathway • Relay molecules are usually protein kinases

46. VI. CELL SIGNALING, cont • Transduction • Non-protein molecule known as cAMP is often second messenger

47. VI. CELL SIGNALING, cont • Response • Nuclear • May “turn on” or “turn off” genes • Cytoplasmic • May regulate enzyme activity • Apoptosis • Controlled cell suicide

48. VI. CELL SIGNALING, cont • Regulation