The Discovery and Structure of Cells: Insights into Cell Theory and Function

1. Ch 4 Cell structure and function

2. Discovery of cells • Early scientists had to make their own microscopes • Better microscopes = better knowledge of microscopic life • Robert Hooke • Observed cork slides • Observed ‘cells’ (like where monks live) • Anton van Leeuwenhoek (10x Hooke’s magnification) • Observed algae and ‘animalcules’ (protists)

3. Other scientists • Mathias Schleiden • Plants are made of cells • Theodor Schwann • Animals are made of cells • Rudolf Virchow • Cells come from other cells • What is the importance of all of these observations?

5. Cell theory • All organisms are made of one or more cells • Cells are the basic units of structure and function in an organism • Cells come from pre-existing cells

6. Cell size • Cells come in many shapes and sizes • Size of a cell is limited by its surface area-to-volume ratio • As a cell grows, volume increases much faster than surface area • If a cell gets too big, materials entering and leaving a cell would not be transported fast enough = cell would starve

7. Cell size Working in pairs, consider two cubes, one with a side that is 1 cm long and the other with a side that is 6 cm long. For each cube calculate: 1. Surface area (= height × width × number of sides) 2. Volume (= height × width × length) 3. Surface area-to-volume ratio (= surface area:volume) What pattern do you observe as the size of the cube increases? What inferences can you make regarding cell size? Take a few minutes to discuss, and then present your conclusions to the class.

8. Answers • Surface area = 6 cm2for the first cube and 216 cm2 for the second cube • Volume = 1 cm3for the first cube and 216 cm3 for the second cube • Surface area:volume= 6:1 for the first cube and 1:1 for the second cube • As the cube size increases, the surface area to volume ratio decreases. • These calculations show why most cells are small (cells must maintain a large surface area to volume ratio in order to function).

9. Parts of a cell • Plasma membrane • aka: Cell membrane • Cell’s outer surface • Barrier • Regulate movement of materials in/out of cell • Cytoplasm: fluid portion of cell • Contains all organelles • NUCLEUS • Control center • Where DNA is located • Or floating in cytoplasm All cells have these 3 parts.

10. Two types of cells • Prokaryotes: lack a nucleus and membrane-bound organelles • Pro- before • Kary- nucleus • Contain a nucleoid: region where DNA is concentrated • *not an organelle • Bacteria and Archea

11. Two types of cells • Eukaryotes: have a nucleus and membrane-bound organelles • Eu- true • Organelles: well defined; intracellular bodies that perform specific functions • All are enclosed in a membrane • Generally larger than prokaryotes

12. Cellular organization • Multicellularity found in more advanced species • Tissue: groups of cells that do a specific job • Organs: tissues that perform a particular job • Organ systems: group of organs that accomplish a related task

13. Plasma membrane (aka: Cell Membrane) The “GATE-KEEPER” • Location: • Surrounds the cell • Functions: • Allows only certain molecules to enter/exit a cell • Separates internal metabolism from external environment • Present in ANIMAL & PLANT cells

14. Plasma Membrane • Composed of a phospholipid bilayer: double layered membrane of phospholipids • Phospholipids • Polar (hydrophillic) heads – oriented to H2O • Nonpolar (hydrophobic) tails – orient away from H2O POLAR NONPOLAR

17. Membrane components • Many proteins are embedded in plasma membrane • Receptor proteins: recognize and bind to substances outside of cell • Enzymes: assist chemrxns • Transport proteins: help substances move across membrane • Fluid mosaic model: phospholipid bilayer behaves like a fluid more than a solid • Lipids and proteins can move around w/in membrane

19. Nucleus Control Center • Houses and protects genetic information • When cell is not dividing, DNA is in chromatin form • Threadlike material • When cell is dividing, DNA is condensed into chromosomes • DNA surrounded by proteins CHROMOSOME

20. Nuclear envelope • Double membrane surrounding nucleus • Nucelar pores regulate movement of materials in/out of nucleus

21. Nucleolus • Nucleolus: structure inside nucleus • Location of ribosomal RNA (rRNA) synthesis • Ribosomes: cell structure responsible for protein sysnthesis • Composed of rRNA

22. Mitochondria Powerhouse • Double-membraned organelle responsible for energy conversion • Organic molecules (glucose + O2) ATP • Inner membrane has many folds  cristae • More surface are = more ATP production • Have their own DNA • Believed to have originated from prokaryotic cells that were incorporated into ancient eukaryotic cells • Symbiotic relationship (both benefit)

23. Endoplasmic reticulum (ER) Freeway • System of membranous tubes and sacs • 2 types • Rough (RER): • Attached ribosomes  protein synthesis • Smooth (SER): • No ribosomes • Tubular appearance • Lipid and steroids synthesis

26. Golgi Apparatus Packaging Center • Location: in cytoplasm • Function: • package and modify proteins or lipids as they pass them from sac to sac • “address labels” • A & P • Double membrane

27. Lysosomes Suicide Sacs • Location: in cytoplasm • Function: • Contain digestive enzymes to break down macromolecules • WBC’s >> break down bacteria • Autophagy: = digestion of old organelles • Autolysis = Cells broken down by their own lysosomes • A & P • Double membrane

28. Peroxisomes • Location: in cytoplasm (especially in liver and kidney cells) • Function: • Similar to lysosomes; contain different enzymes • Neutralize free radicals (damaging Oxygen ions) • Detoxify alcohol and other drugs • Produce H2O2 (hydrogen peroxide) • A & P • Double membrane

29. *PROTEIN SYNTHESIS • Ribosomes (on Rough ER) make proteins. • Vesicles transport proteins to Golgi apparatus. • Golgi modifies and packages proteins in new vesicles. • Vesicles release proteins that are needed OUTSIDE the cell. • Vesicles with ENZYMES stay inside the cell as • Lysosomes • Peroxisomes • Endosomes

30. CYTOSKELETONMicrotubules • Small hollow tubes anchored near nucleus • Location: cytoplasm • Function: • Hold organelles in place • Maintain cell shape • “tracks” to guide movement of organelles and molecules within cell • A & P

31. CYTOSKELETONMicrofilaments • Small threads wrapped around each other • Location: cytoplasm • Function: • Cell movement • Muscle contraction • WBC crawl • A & P

32. CYTOSKELETONIntermediate Filaments • Location: nucleus & cytoplasm • Function: • Anchor nucleus & some organelles • Maintain shape of nucleus • A & P

33. Cilia & Flagella • Location: surface of cell • Function: • Assist in movement • CILIA = tiny hairs • FLAGELLA = tails • Made of microtubules • A & P

34. Centrioles • Location: cytoplasm • Function: • Assist in MITOSIS (cell division) • Made of microtubules • A

35. PLANT CELLSCell Wall • Location: OUTSIDE plasma membrane • Made of CELLULOSE (carbohydrate) • Function: • Form rigid wall • Helps cells maintain same shape • P • Double membrane sometimes if secondary cell wall forms (i.e. wood)

36. PLANT CELLSCentral Vacuole • Location: Cytoplasm • Function: • Acts as a reservoir for large amounts of water • Also: enzymes, wastes, etc. • When empty, plant wilts. • P • Single membrane

37. PLANT CELLSChloroplasts • Similar to mitochondria • Contain own DNA • Location: Cytoplasm • Function: • PHOTOSYNTHESIS • Light energy converted into chemical energy (glucose) • *Contain green pigment • P • Double membrane

38. PLANT CELLSChromoplasts & other plastids • Location: Cytoplasm • Function: • Give color to plants • Carrots = orange pigment • Daisies = yellow pigment • A & P • Double membrane