BIOL 2021 Lecture Notes - Lecture 10: Vacuole, Extracellular Fluid, Endosome
12 May 2018
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• Question: How does the low PH of lysosomes protect the rest of the cell form
lysosomal enzymes in case the lysosome breaks?
o Answer: Lysosomal enzymes are acid hydrolases with optimal pH of 5.0.
The cytosol is pH 7.2, and the lysosomal enzymes would be inactive.
• Question: How else could the cell use the PH gradient across the lysosomal
membrane? As an energy source for transport of metabolites across the
membrane.
• Fig 13-40 plant cell vacuole
o Vacuoles in plants and fungi are related to animal cell lysosomes and
contain a variety of hydrolytic enzymes, but their functions are remarkably
diverse.
o Plant and fungal vacuoles = lysosomes.
o Used for storage, degradation, osmotic pressure and size regulation.
• Formation of lysosomes
• Fig 13-42 pathways to lysosomes
o Digestive enzymes delivered from ER > Golgi > endosomes > lysosomes.
o Endosome becomes lysosome = maturation.
o The best studied of these degradation paths is the one followed by
macromolecules taken up from extracellular fluid by endocytosis. A similar
pathway found in phagocytic cells, such as macrophages and neutrophils
in vertebrates, is dedicated to the engulfment, or phagocytosis, of large
particles and microorganisms to form phagosomes. A third pathway called
macropinocytosis specializes in the nonspecific uptake of fluids,
membrane, and particles attached to the plasma membrane. We will
return to discuss these pathways later in the chapter. A fourth pathway
called autophagy originates in the cytoplasm of the cell itself and is used
to digest cytosol and worn-out organelles, as we discuss next.
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