Cell Bio Lecture 3.8.25

Key Concepts in Cell Movement and Cytoskeleton Dynamics

  • Attachment Points in Cell Movement

    • The attachment point serves as a foundation for the actin network to exert forces.
    • Without an attachment, actin filaments can slide over each other without generating significant movement.
    • Mechanical work facilitated by the attachment point is essential for cell movement, allowing the leading edge to protrude while the rear contracts.

  • Roles of Actin Networks

    • Actin filaments can associate and cross-link via proteins, with motor proteins like myosins playing a critical role.
    • The actin-myosin network is essential for pushing the leading edge forward and pulling the rear of the cell, emphasizing the importance of attachment.

  • Protrusion vs. Contraction

    • Protrusion: Forward movement of the cell's leading edge facilitated by actin assembly.
    • Contraction: Rear of the cell contracts to move forward, relying on the contractile network at the rear powered by myosins.

  • Movement Dynamics Without Attachment

    • If actin is added without a connection, actin could slide back rather than push the membrane forward, highlighting the need for stable adhesion to the substrate.
    • The attachment of the cell to its substrate creates a leverage point, permitting effective movement rather than mere sliding.

  • Focal Adhesions and GTPases

    • Focal Adhesions: Dynamic structures that enable the cell to attach to the substrate, regulated by monomeric GTPases.
    • They can reposition as the cell moves, allowing for continued movement through the cytoskeletal network.
    • Monomeric GTPases like RAC and Rho play vital roles in regulating the actin network and are crucial for cell motility.

  • Functionality of Monomeric GTPases

    • RAC: Stimulates protrusions at the leading edge by promoting branched actin networks without substantial myosin engagement, leading to a web-like protrusion.
    • Rho: Activates linear actin polymerization coordinated with myosin to create contractile networks at the back of the cell, assisting with retraction and forward motion.
    • Inhibition between RAC and Rho ensures proper spatial distribution and function of these GTPases, corresponding to their respective roles in movement.

  • Cytoskeletal Components Summary

    • Actin: Key player in cell movement, with diverse regulatory proteins.
    • Microtubules: Involved in vesicle transport and cell division, regulated by GTP binding and hydrolysis.
    • Intermediate Filaments: Less dynamic, structural roles without nucleotide triphosphates.

  • Research Opportunities in Laboratory Classes

    • CURE (Course-based Undergraduate Research Experiences) provide students with research exposure while fulfilling lab course requirements.
    • Benefits include genuine research experience and lower stress environments conducive to learning.

  • Signaling and Protein Trafficking

    • Discussed processes of protein translocation into the ER and Golgi for modification & sorting, emphasizing the significance of glycosylation as markers for cellular progression.
    • Reviewed recycling and degradation pathways for receptors, focusing on mechanisms such as endocytosis and autophagy.

  • Summary Takeaways for Exam Preparation

    • Focus on the mechanisms of actin dynamics and the role of GTPases in cellular movement and stability.
    • Understand the significance of focal adhesions in motility and their regulatory structures.
    • Review how different cellular processes (like protein trafficking) integrate with the cytoskeletal framework during vesicle movement and signal reception.