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The Cell

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The Cell

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  1. The Cell Chapter 6

  2. History of Cytology • Initial microscopes • Robert Hooke • Origin of term cell • Antoni Van Leeuwenhoek • First to visualize living cells • Cell Theory developed by Schleiden, Schwann, and Virchow • Every organism is composed of 1+ cells • A cell is the simplest unit to demonstrate the properties of life • Cells arise only from previously existing cells

  3. Visible light is refracted (bent) through glass lenses Magnification is ratio of image size to real size Resolution is minimum distance 2 points can be separate and still distinguishable Light Microscopy

  4. Electron Microscope (EM) Scanning (SEM) Transmission (TEM) Details of cell surfaces, 3D image Details of internal cell structures • Uses a beam of electrons = higher resolution • Can’t use on living cells

  5. Similarities in All Living Cells • Plasma membrane: allows selective passage of molecules • Double layer of phospholipids • Variety of proteins spread throughout • Varies with cell location and function • Cytosol or cytoplasm: semisolid substance enclosed by the plasma membrane • Chromosome(s): carry genes as DNA • Ribosomes: tiny complexes that make proteins (genes direct)

  6. Cellular Classification • Prokaryotes- before nucleus • NO nucleus (nucleoid region) • NO organelles • Single, circular DNA • Smaller, less complex • E.g bacteria, archaea • Eukaryotes- true nucleus • Nucleus • Membrane bound organelles • DNA arranged on multiple chromosomes • Larger • E.gprotists, fungi, plants, animals

  7. The Simplicity of Cells • Many small cells advantaged over few large cells • As cells grow, volume increases faster than surface area • Ratio constrains size b/c limits amount of nutrients in and wastes out • Effects shapes and body plans too

  8. Eukaryotic Cell Types Plant Animal

  9. Genetic Control of the Cell • Nucleus is the control center that directs the cell • Enclosed by a double membrane called a nuclear envelope • Nuclear pores allow substances to enter and leave • Nuclear lamina protein filaments that maintain shape • Chromosomes are the structures that carry genetic info • Consists of chromatin, a protein and DNA structure that coils before cell division • Nucleolus is where rRNA is synthesized from DNA instructions • Form small and large subunits that exit the nuclear pores to form ribosomes in the cyoplasm

  10. Ribosomes • Use DNA to make proteins • Made of rRNA and protein complexes • Build proteins in 2 locations • Free ribosomes formed in cytosol • Proteins will remain/function in cytosol • Bound ribosomes are attached to endoplasmic reticulum or nuclear envelope • Make proteins that are shipped out of initial cell • Can change building location/type • Structurally identical

  11. Trafficking and Metabolism • Endomembrane system • Multiple responsibilities • Related through connections or vesicle transport • Endoplasmic reticulum • Separates internal compartment of ER from cytosol • Smooth ER lacks ribosomes • Synthesis lipids and carbs; detoxes alcohol and poisons • Detox induces proliferation = increase tolerance to drugs • Rough ER • Site of protein synthesis • Secrete proteins in vesicles that bud from membrane • Expands itself (makes own phospholipids)

  12. Golgi Apparatus • Modifies, stores, and sends products elsewhere • Cis = closest to Er • Receive vesicles from ER • Trans = opposite side • Ships products in vessels • Modified as move between two sides • Manufactures and refines products in stages

  13. Lysosomes • Made by rough ER and sent to golgi • Use hydrolytic enzymes to phagocytize food or damaged organelles • Best in acidic conditions • Decreased reaction if they break open • Can lead to cell destruction • Fuse with phagocytotic cells to break down polymers • E.g WBC’s attack and destroy bacteria • Autophagy recycles cell’s own materials • Continuous renewal of cell

  14. Vacuoles • Used for storage or transport of substances made by the ER • Contractile vacuoles removeexcess water from cell • Hydrolysis in plants and fungi b/c no lysosomes • Central vacuole transports solutes in plant cells; disposes of by-products • Pigmented to attract pollinators and signal poisonous

  15. Exchanging Energy • Mitochondria • Convert E to usable forms • Site of cellular respiration = synthesis of ATP • Number in a cell is related to membrane activity • 2 membranous layers • Innermost layered is folded to form cristae • Matrix is enclosed by inner and outer membranes • Chloroplasts • Contain chlorophyll or green pigment • Found in leaves and green plants • 2 membrane layers • Innermost is a group of interconnected sacs called thylakoids • Stacks are grana • Fluid outside thylakoids is the stroma

  16. Peroxisomes • Transfer H to O2 = H2O2 (hydrogen peroxide) • Break down fatty acids • Detoxify alcohol in liver • Don’t bud from ER, grow by incorporating proteins from cytosol and lipids

  17. Microtubules • Thickest fibers, made of dimers of tublin (α- and β) • A ring of 9 triplets comprise a centriole produced in a centrosome • Produce spindle fibers during cell division • Provides the mobility of cilia • Beat like an oar • A ring of 9 doubles and 2 singles produce a flagella

  18. Microfilaments • Solid rods of double twisted actin subunits • Sometimes mixed with myosin • Form structural networks • Allow dynein, a large motor protein to ‘walk’ • Interactions allow amoebas to move pseudopodia

  19. Intermediate Filaments • Made of different protein subunits including keratin • Maintain and bear tension • Remain after death • E.g keratinized skin