Class Schedule and Exam Information

  • Class Schedule:

    • Classes resume Monday, Wednesday, and Friday after the holiday.

    • Content learned after the holiday will be on the following exam scheduled for Thursday and Friday.

    • Final exam will be cumulative and will cover material from all classes.

    • The final includes:

    • Multiple choice and short answer questions based on new content.

    • Longer essay questions on cumulative material.

Overview of Topic Covered

  • Previous Topics:

    • Budding and vesicle formation.

  • Key Component of Vesicle Formation:

    • Donor Compartment:

    • Examples include:

      • Golgi apparatus.

      • Endoplasmic reticulum (ER).

      • Plasma membrane (especially relevant during endocytosis, where vesicles can be formed from the plasma membrane).

Vesicle Composition and Membrane Structure

  • Vesicle Cargo:

    • Cargo must be anchored within vesicles.

  • Membrane Structure:

    • Phospholipid bilayer structure is vital for proper function.

    • Phospholipids have hydrophilic (polar) heads and hydrophobic (nonpolar) tails, creating bilayers that allow adequate folding of proteins within an aqueous lumen.

  • Differences within compartments:

    • The internal environment of compartments (like the ER lumen) differs in concentration of ions (e.g., calcium) compared to the cytosol but remains aqueous.

Cytoskeletal Involvement

  • Movement Mechanism:

    • Vesicles travel along microtubules or actin filaments utilizing motor proteins.

    • Motor Proteins:

    • Proteins that enable vesicular transport to specific cellular sites.

Tethering and Fusion Process

  • Tethering Factors:

    • Interact with RAB GTPases to help clearly target vesicles to acceptor membranes (specific organelles).

    • Example in Synaptic Vesicle Cycle:

    • RAB proteins facilitate vesicle transport to the plasma membrane for neurotransmitter release upon calcium influx.

  • GTPases Overview:

    • Small GTPases play a role in the activation and deactivation of processes related to vesicle trafficking.

    • Common types of GTPases discussed:

      • RAN (nuclear transport).

      • RAB (vesicle trafficking).

      • RAD (not extensively discussed).

  • Function of GTP and GDP in GTPases:

    • GTP (guanosine triphosphate) is a nucleotide involved in energy transfer and signaling.

    • GTP hydrolysis produces GDP (guanosine diphosphate) and a phosphate group, deactivating the GTPase.

    • Importance of GTP is in providing a switch-like function for various processes, including vesicle fusion and trafficking.

Mechanism of Action of GTPases

  • GTP Hydrolysis Process:

    • GTPase hydrolyzes GTP to GDP and a phosphate:

    • GAP (GTPase Activating Proteins) aid in speeding up the hydrolysis process.

    • GEF (Guanine Exchange Factors) facilitate the exchange of GDP for GTP to reactivate the GTPase.

Regulation of RAB GTPases

  • Interaction with GDI (Guanine Nucleotide Dissociation Inhibitor):

    • Rab GDP bound to GDI keeps the GTPase inactive in cytoplasm until the appropriate signals for activation occur.

    • An additional regulatory mechanism that does not occur in the nucleus due to differing compartments.

Rab GTPases Specificity and Function

  • Different Types:

    • Various RAB proteins correspond to specific transport routes, influencing which vesicles interact with which membranes.

    • Tethering proteins and RAB GTPases ensure precision in vesicle trafficking, as they can attract vesicles to specific membranes crucial for proper signaling.

SNARE Proteins in Vesicle Fusion

  • Types of SNARE Proteins:

    • v-SNAREs are located on vesicles; t-SNAREs are on the target membrane.

    • Upon interaction, they coil together to pull the vesicle close to the target membrane.

  • Analogy Used:

    • The interaction of SNAREs is akin to how corded phones tangle when twisted; they physically pull vesicles into their target membranes.

Upcoming Topics

  • Next Lecture Content:

    • Explore lysosomal functions and the ubiquitin-proteasome system, focusing on degradation processes.

    • The discussion will begin next Monday, with the plan to continue progressing through the material systematically.