Lecture 9 (Sept 17)

Lecture 9 (Sept 17) - Biological Sciences 110A:...

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 Overview of the endomembrane organelles  Membrane and protein trafficking (secretion)  Signal Hypothesis: cytosol to ER  Molecular chaperones and protein folding  Formation of glycoproteins (glycosylation) Biological Sciences 110A: Introduction to Biology Kendal Broadie Reading Chapter 8: 274-298 Karp
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Eukaryotic cells have many membrane-bound organelles Cytosol  (many, many processes) Nucleus  (DNA genome, transcription and RNA  processing) ER  (synthesis of secretory and membrane proteins;  lipid metabolism)   Golgi  (processing and sorting of secretory and  membrane proteins) Endosomes  (processing and sorting incoming  materials) Lysosomes  (degradation/recycling) Peroxisomes  (detoxification) Mitochondria  (ATP synthesis) Chloroplasts  (photosynthesis)   See Fig. 8.1 Karp
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Relative numbers/volumes of some membrane-bounded organelles in  “typical” mammalian cell How are these membrane compartments maintained?
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Membrane flows throughout the endomembrane structures  continuously and rapidly Membrane is internalized from the plasma membrane through a  “vesicle budding”  pro c e s s  c a lle d  endocytosis . ~2-3%  o f the  m e m b ra ne  inte rna lize d pe r m inute ! Me m bra no us   vesicles fuse  with o rg ane lle s  to  de live r m e m b ra ne  and ve s ic le  c o nte nts .  Fus io n with the  plas m a m e m b rane  c a lle d  exocytosis .   The entire membrane is recycled in less than 1 hr… See Fig. 8.2 Karp
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Membrane flow during exocytosis and endocytosis  is a delicate balance… Endocytosis internalizes membrane ~2-3% per  minute Exocytosis recycles entire membrane in less than 1  hr Block endocytosis, exocytosis continues: membrane area grows
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Membrane flow during exocytosis and endocytosis  is a delicate balance Block exocytosis, endocytosis continues: membrane area shrinks Endo c yto s is  inte rnalize s  m e m b rane  ~2- 3%  pe r m inute Exo c yto s is  re c yc le s  e ntire  m e m bra ne  in  le s s  than 1 hr
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Briefly (minutes) label newly  made proteins in secretory cell  with radioactive amino acids ( 3 H- leucine,  14 C-leucine,  35 S- methionine) Fix and process cell     for  sectioning and microscopy Overlay section with  photographic emulsion Expose photographic emulsion  (weeks to months!); silver grains  reveal radioactivity
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Lecture 9 (Sept 17) - Biological Sciences 110A:...

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