Cellular Organelles, Membrane Transport, and Cytoskeleton

  • Administrative Points & Upcoming Schedule:

    • Clicker questions during the first part of the lecture are normal, but later quiz questions will be graded.
    • Quiz questions are based on content from the past two classes, focusing on the endomembrane system.
    • Students must watch videos in the post-work folder for Chapter 44, Class 1010, as quiz questions on Wednesday will cover the endomembrane system.
    • Pre-work for Chapter 55 is also assigned.
    • Wednesday's lecture will cover cell membranes, osmosis, membrane transport, and hypertonic/hypotonic solutions.

  • Endomembrane System Overview:

    • The endomembrane system is a pathway for proteins to travel to various organelles (e.g., lysosomes, Golgi, ER) or to be secreted from the cell.
    • Some proteins, such as those going to mitochondria, chloroplasts, or back to the nucleus, do not follow this system.

  • Peroxisomes:

    • Function: Carry out reactions that break down toxic substances.
    • Waste Products: Produce highly damaging waste products, such as hydrogen peroxide (H<em>2O</em>2)(H<em>2O</em>2), which is used as a disinfectant but also kills living tissue.
    • Significance: Demonstrates the importance of separating chemical reactions from the rest of the cytoplasm to prevent cellular damage.
    • Origin (Still Studied): The exact origin is unknown, though some membrane material is replaced by vesicles from the smooth ER and rough ER.

  • Lysosomes - The Cell's Recycling Center:

    • Part of Endomembrane System: Lysosomes are a crucial component of the endomembrane system.
    • Contents: Contain over 4040 different digestive enzymes, which arrive via the endomembrane system pathways.
    • Job: Break down various cellular components.
    • Cargo:
      • Old, Broken-Down Organelles: Proteins tag damaged organelles (e.g., fragmented mitochondria) for destruction; other proteins then ensure these degraded parts (organelles, proteins, fragments) are delivered to the lysosome.
      • External Cargo: Receive cargo that has entered the cell from the outside.
    • Recycling Process: Lysosomes break down macromolecules into their smallest units: amino acids, monosaccharides, and individual lipids.
    • Reuse: These broken-down building blocks are then sent into the cytoplasm for the cell to reuse as raw materials for new structures.
    • **Autophagy -