Cell Structure and Function: A Tour of the Cell

1. Chapter 6 A Tour of the Cell

2. CELL THEORY • All organisms are made of one or more cells. • Cells are the basic unit of structure and function in living things • Cells arise by division of pre- existing cells.

3. How do we study cells? Cytology • Microscopes • Light microscopes • Electron microscopes • Transmission (TEM) • Scanning electron microscope (SEM)

4. Comparisons of Scopes Light Electron • Visible light passes through specimen • Refracts light so specimen is magnified • Magnify up to 1000X • Specimen can be alive/moving • Color • Can’t see organelles other than nucleus • Focuses a beam of electrons through/onto specimen • Magnify up to 1,000,000 times • Specimen non-living and in vacuum • Can see organelles

5. Electron Microscopy Transmission (TEM) Scanning (SEM) • 2-D, study internal structures of cells • Creates a flat image with extreme detail • Can enhance contrast by staining atoms with heavy metal dyes • Images called a micrograph • 3-D • Used for detailed study of surface of specimen • Gives great field of depth • Sample covered with thin film of gold, beam excited electrons on surface

6. Studying cell structure & function • Cell fractionation- take apart cells, separate major organelles • Ultracentrifuge- applies force 1 million times the force of gravity to separate further the cell organelles with the most dense at the bottom

7. Cell Size and Scale https://www.youtube.com/watch?v=wuXSEOKNxN8&feature=related- why small 6 min anderson

8. As cell size increases, the SA/V ration decreases, rates of chemical exchange may then be inadequate for cell size • Cells must remain small to maintain a large surface area to volume ratio • Large S.A. allows increased rates of chemical exchange between cell and environment

9. 2 Types of Cells: • Prokaryotes: Domain Bacteria & Archaea • Eukaryotes (Domain Eukarya): Protists, Fungi, Plants, Animals

10. Prokaryote Vs. Eukaryote • No nucleus (Nucleoid-DNA concentration) • DNA in a nucleoid • Cytoplasm/Cytosol • No organelles other than ribosomes • Small size • Primitive • i.e. bacteria • Has nucleus and nuclear envelope • Cytoplasm/Cytosol • Membrane-bound organelles with specialized structure/function • Much larger in size • More complex • i.e. plant/animal cell

11. Nucleus • Function: control center of cell • Contains genetic material • Surrounded by double membrane with pores(nuclear envelope) • Continuous with the rough ER • Nuclear side of envelope lined with a network of protein filaments (Nuclear Lamina)- maintain shape • Nuclear pores: control what enters/leaves nucleus • Chromatin: complex of DNA + proteins; makes up chromosomes • Nucleolus: region where ribosomal subunits are formed

12. Ribosomes • Function: protein synthesis • Composed of rRNA + protein • Large subunit + small subunit • Types: • Free ribosomes: float in cytosol, produce proteins used within cell • Bound ribosomes: attached to ER, make proteins for export from cell

13. Endomembrane System: -Regulates protein traffic & performs metabolic functions - Includes: nuclear envelope, ER, Golgi, Lysosomes, Vacuoles, and Plasma Membrane

14. TO: TO: TO: endoplasmicreticulum nucleus proteinon its way! DNA RNA vesicle vesicle ribosomes TO: protein finishedprotein Golgi apparatus Making Proteins

15. Endoplasmic Reticulum (ER) • Network of membranes and sacs that are continuous with nuclear envelope • Types: • Rough ER: ribosomes on surface • Function: package proteins for secretion, send transport vesicles to Golgi, make replacement membrane • Smooth ER: no ribosomes on surface • Function: synthesize lipids, metabolize carbs, detox drugs & poisons (in liver), store Ca2+(muscles)- helps regulate muscle contraction

16. Golgi Apparatus • Function: modify, store, & ship proteins • Flattened sacs of membranes arranged in stacks • Cisternae: flattened membranous sacs that receives vesicles • Cis Face : receiving Trans face: shipping

17. Lysosomes • Function • little “stomach” of the cell • digests macromolecules • “clean up crew” of the cell • cleans up broken down organelles • Structure • vesicles of digestive enzymes only in animal cells synthesized by rER, transferred to Golgi

18. But sometimes cells need to die… • Lysosomes can be used to kill cells when they are supposed to be destroyed • programmed development • control of cell growth • some cells have to die for proper development in an organism • apoptosis • “auto-destruct” process • lysosomes break open & kill cell • ex: tadpole tail gets re-absorbed when it turns into a frog • ex: loss of webbing between your fingers during fetal development

19. Peroxisomes- digestive enzyme sac • Functions: break down fatty acids to sugars; detox cell of alcohol and other poisons • Found in plants and animals • Involves production of hydrogen peroxide (H2O2) , which is broken down by catalase (imports H) resulting in water and oxygen • Glyoxysomes: convert oils to sugars in seeds for energy source

20. Vacuoles & vesicles • Vesicles: transporting • Vacuoles: storing • Food vacuoles • phagocytosis, fuse with lysosomes • Contractile vacuoles • in freshwater protists, pump excess H2O out of cell • Central vacuoles • in many mature plant cells, • Stockpile proteins, hold pigments, Store defense compounds

21. + Energy Organelles • Cells must convert incoming energy to forms that they can use for work • mitochondria: from glucose to ATP • ATP = active energy • chloroplasts: from sunlight to ATP & carbohydrates • carbohydrates = stored energy • https://www.youtube.com/watch?v=ZrNt1FaUxe0 8 min ATP ATP

22. Chloroplasts- PLANTS ONLY • Function: site of photosynthesis (converts light energy into chemical energy ie. carbohydrates) • Contains chlorophyll (green pigment) for capturing sunlight energy Why internal sac membranes? increase surface area for membrane-bound enzymes that synthesize ATP

23. + water + energy  glucose + oxygen carbon dioxide light energy  + 6CO2 + 6H2O + 6O2 C6H12O6 Membrane-bound Enzymes

24. Mitochondria- Powerhouse • Function: site of cellular respiration (use oxygen to make ATP, breaks down carbohydrates) • Generate ATP in presence of Oxygen • Break down larger molecule into smaller to generate energy= catabolism • Generate energy in presence of Oxygen (aerobic respiration) • number of mitochondria is correlated with aerobic metabolic activity • more activity = more energy needed = more mitochondria Why 2 membranes? increase surface area for membrane-bound enzymes that synthesize ATP

25. glucose + oxygen  carbon + water + energy  C6H12O6 + 6O2 6CO2 + 6H2O + ATP dioxide Membrane-bound Enzymes

26. The Great ENERGY Circle of Life sun Photosynthesis ATP plants glucosesugar O2 + CO2 + H2O Respiration animals & plants ATP

27. Endosymbiont theory • Mitochondria & chloroplasts share similar origin • Prokaryotic cells engulfed by ancestors of eukaryotic cells • Evidence: • Double-membrane structure • Transform energy • Have own ribosomes & circular DNA, enzymes • Reproduce independently within cell • Semi-autonomous (move, divide, change shape)

28. Harvard cell video http://multimedia.mcb.harvard.edu/anim_innerlife.html

29. Cytoskeleton: network of protein fibers that extends from nucleus to plasma membrane in eukaryotic cells • Functions: • Structural Support • Maintain shape of cell • Provide anchorage for organelles [protein fibers: microfilaments, intermediate filaments, microtubules] • b) Motility • - Cell motion [cilia and flagella] • c) Regulation • - Organize structures and activities of cell

30. Main function: Structural support and cell movement ~ Move chromosomes during cell division Centrioles & spindle fibers ~ tracks guide motor proteins Motor proteins: dynein & myosin ~ cell motility ex. Cilia & flagella • Main function: Structural support and cell movement • ~ Move chromosomes during cell division • Centrioles & spindle fibers • ~ tracks guide motor proteins • Motor proteins: dynein & myosin • ~ cell motility ex. Cilia & flagella

31. 1) Move chromosomes during cell division ex. Centrioles & spindle fibers Centrosomes: region from which microtubules grow • Also called microtubule organizing center • Animal cells contain centrioles • In animal cells, the centrosome has a pair of centrioles, ,each with 9 triplets of microtubules in a ring. During cell division, centrioles replicate

32. http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb2/part1/movies/kinesin.dcrhttp://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb2/part1/movies/kinesin.dcr Vesicle Receptor for motor protein Motor protein (ATP powered) Microtubule of cytoskeleton MICROTUBULES 2)Tracks guide motor proteins to destination (Motor proteins: dynein and kinesin protein)

33. 3) cell motility ex. Cilia & flagella • Are locomotor appendages • 9 pairs of microtubules around 2 single microtubules in center (9 + 2 pattern) • Extensions of cytoskeleton Examples: -Many unicellular protists move with flagella -Some plant reproductive cells have flagella -Cilia in oviducts move egg toward uterus -Cilia lining windpipe sweep mucous out of lungs -Flagellum in sperm cells

34. The bending of cilia and flagella is driven by the arms of a motor protein, dynein. • Addition to dynein of a phosphate group from ATP and its removal causes conformation changes in the protein. • Dynein arms alternately grab, move, and release the outer microtubules. • Protein cross-links limit sliding and the force is expressed as bending.

35. Nonmoving cytoplasm (gel) Chloroplast Streaming cytoplasm (sol) Muscle cell Parallel actin filaments Cell wall Actin filament Myosin filament Myosin arm (a) Myosin motors in muscle cell contraction. MICROFILAMENTS • STRUCTURE • Thinnest class of fibers • Made of Actin monomers • Twisted double chain of actin subunits ~ 7 nm in diameter • FUNCTION • Crosslinks with microtubules (cell shape) • Muscle cells: Actin filaments interact with myosin motor proteins to create muscle contraction • Amoeboid movement • Cytoplasmic streaming

36. https://www.youtube.com/watch?v=FoDniO676Dw&feature=related NUCLEAR LAMINA

37. 3 Types of Cytoskeleton Fibers: • Protein = tubulin • Largest fibers • Shape/support cell • Track for organelle movement • Forms spindle for mitosis/meiosis • Component of cilia/flagella • MP: Kinesin, Dynein • Protein = actin • Smallest fibers • Support cell on smaller scale • Cell movement • Eg. amoeboid movement, cytoplasmic streaming, muscle cell contraction • MP: Myosin • Protein-keratin • Intermediate size • Permanent fixtures • Maintain shape of cell • Fix position of organelles

38. Plant Cells • Cell wall: protect plant, maintain shape, prevents excessive uptake of water • Composed of polysaccharide cellulose

39. Unify plant into one living continum

40. Extracellular Matrix (ECM) • Animal cells lack a cell wall so they have ECM • Outside plasma membrane • Function: Strengthens tissues and transmits external signals to cell; functions for support, adhesion, movement, regulation • Glycoproteins: ex. Collagen- forms strong fibers outside the cells, accounts for 50% of total protein in the body; embedded in a network woven from proteoglycans (small protein with many carb. chains covalently attached). These attach to polysaccharide molecules. • Integrins: membrane protein with 2 subunits, bind to the ECM on one side and proteins on the other. Linkage allows the cell to transmit signals between interior and exterior • Fibronectin: attaches to ECM to integrins embedded in plasma membrane

41. Intercellular Junctions (Animal cells) • Tight junctions: 2 cells are fused to form watertight seal, continuous seal, prevent leakage; skin and bladder • Desmosomes: “rivets” that fasten cells into strong sheets (anchoring junctions); muscles, uterus • Gap junctions: channels through which ions, sugar, small molecules can pass (communicating junctions); heart cells