Proteins on the inner surface of the lysosomal membrane are spared by digestion

Proteins on the inner surface of the lysosomal

This preview shows page 5 - 7 out of 10 pages.

Proteins on the inner surface of the lysosomal membrane are spared by digestion by their three-dimensional conformations, which protect vulnerable bonds from hydrolysis. Lysosomes carry out intracellular digestion in a variety of circumstances. Amoebas eat by engulfing smaller organisms by phagocytosis. The food vacuole formed by phagocytosis fuses with a lysosome, whose enzymes digest the food. As the polymers are digested, monomers pass to the cytosol to become nutrients for the cell. Lysosomes can play a role in recycling of the cell’s organelles and macromolecules. This recycling, or autophagy, renews the cell. During autophagy, a damaged organelle or region of cytosol becomes surrounded by membrane. A lysosome fuses with the resulting vesicle, digesting the macromolecules and returning the organic monomers to the cytosol for reuse. The lysosomes play a critical role in the programmed destruction of cells in multicellular organisms. This process plays an important role in development. The hands of human embryos are webbed until lysosomes digest the cells in the tissue between the fingers. This important process is called programmed cell death , or apoptosis.
Image of page 5

Subscribe to view the full document.

Vacuoles have diverse functions in cell maintenance. Vesicles and vacuoles (larger versions) are membrane-bound sacs with varied functions. Food vacuoles are formed by phagocytosis and fuse with lysosomes. Contractile vacuoles, found in freshwater protists, pump excess water out of the cell to maintain the appropriate concentration of salts. A large central vacuole is found in many mature plant cells. The membrane surrounding the central vacuole, the tonoplast, is selective in its transport of solutes into the central vacuole. The functions of the central vacuole include stockpiling proteins or inorganic ions, disposing of metabolic byproducts, holding pigments, and storing defensive compounds that defend the plant against herbivores. Because of the large vacuole, the cytosol occupies only a thin layer between the plasma membrane and the tonoplast. The presence of a large vacuole increases surface area to volume ratio for the cell. Concept 6.5 Mitochondria and chloroplasts change energy from one form to another Mitochondria and chloroplasts are the organelles that convert energy to forms that cells can use for work. Mitochondria are the sites of cellular respiration, generating ATP from the catabolism of sugars, fats, and other fuels in the presence of oxygen. Chloroplasts, found in plants and algae, are the sites of photosynthesis. They convert solar energy to chemical energy and synthesize new organic compounds such as sugars from CO 2 and H 2 O.
Image of page 6
Image of page 7
  • Fall '16
  • idk

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Ask Expert Tutors You can ask 0 bonus questions You can ask 0 questions (0 expire soon) You can ask 0 questions (will expire )
Answers in as fast as 15 minutes