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					    Chapter 6F cont.
    The Cell:
    Endomembrane System–
        Lysosomes, Peroxisomes,
        Vacuoles, Vesicles


AP Biology
   Lysosomes
    § Structure
         u   membrane-bounded sac of hydrolytic
             enzymes that digests macromolecules
             § enzymes & membrane of lysosomes are
               synthesized by rough ER & transferred to
               the Golgi




        only in
        animal cells
AP Biology
                                                    1960 | 1974
   Lysosomes
    § Function
         u   a little “stomach” for the cell
              § lyso– = breaking things apart
              § –some = body
         u   also the “clean up crew” of the cell



Why was this discovery
so important?

                   1974 Nobel prize: Christian de Duve
AP Biology         Lysosomes discovery in 1960s
   Cellular digestion
   § Lysosomes fuse with food vacuoles
   § Polymers are
      digested into
      monomers
       u     pass to cytosol
             to become nutrients
             of cell




AP Biology
                                    Where old proteins go to die!
   The Recycler
     Fuse with organelles or macromolecules in cytosol to
     recycle materials




AP Biology
   Lysosomal enzymes
     § Lysosomal enzymes work best at pH 5
         u   organelle creates custom pH
         u   how?
              § proteins in lysosomal membrane pump H+ ions from
               the cytosol into lysosome
         u   why?
              § enzymes are very sensitive to pH
         u   why?
              § enzymes are proteins — pH affects structure
         u   why evolve digestive enzymes which function at
             pH different from cytosol?
              § digestive enzymes won’t function well if leak into
               cytosol = don’t want to digest yourself!
AP Biology
   When things go wrong…                          Tay-Sachs
     § What if a lysomome digestive
        enzyme doesn’t function?
         u   don’t digest a biomolecule
              § instead biomolecule collects in
                lysosomes
              § lysosomes fill up with
                undigested material
         u   lysosomes grow larger & larger
              § eventually disrupt cell & organ
                function
     § “Lysosomal storage diseases”
        are usually fatal
         u   Tay-Sachs disease
              § lipids build up in brain cells
              § child dies before age 5


AP Biology
   Sometimes its supposed to work
   that way…
    § Apoptosis = cell death
         u   critical role in programmed destruction
             of cells in multicellular organisms
              § auto-destruct mechanism
                  w “cell suicide”
              § some cells have to die in an organized
                fashion, especially during development
                  w ex: development of space between your fingers
                   during embryonic development
                 w ex: if cell grows improperly this self-destruct
                   mechanism is triggered to remove damaged cell
                     n cancer over-rides this to enable tumor growth

AP Biology
                        syndactyly
    Fetal development



                               15 weeks




6 weeks


 AP Biology
AP Biology
   Peroxisomes
    § Other digestive enzyme sacs
         u in both animals & plants
         u breakdown fatty acids to sugars

              § easier to transport & use as energy source
         u   detoxify cell
              § detoxifies alcohol &
                other poisons
         u   produce peroxide (H2O2)
              § must breakdown
               H 2O 2 ® H 2O

AP Biology
   Vacuoles & vesicles
    § Function
         u   little “transfer ships”
              § Food vacuoles
                 w phagocytosis, fuse with lysosomes
              § Contractile vacuoles
                 w in freshwater protists, pump excess H2O
                   out of cell
              § Central vacuoles
                 w in many mature plant cells



                           “Let’s go to the video tape!”
AP Biology                        (play movie here)
   Vacuoles in plants
    § Functions
         u   storage
             § stockpiling proteins or inorganic ions
             § depositing metabolic byproducts
             § storing pigments
             § storing defensive
               compounds against
               herbivores
             § selective membrane
                w control what comes
                  in or goes out￿

AP Biology
             §Vacuole




AP Biology
§Vesicles




AP Biology
             Vesicles
   Putting it all together…




AP Biology

				
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posted:7/17/2013
language:Latin
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