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Vesicular Budding, Transport, and Coat Proteins quiz #1

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  • What are the main types of vesicle coat proteins, and what roles do they play in vesicular transport within the cell?
    The main types of vesicle coat proteins are clathrin, COPI, and COPII. Clathrin is important for vesicle formation at the plasma membrane and between the Golgi and plasma membrane. COPI mediates transport from the Golgi to the ER (retrograde), while COPII is involved in budding vesicles from the ER to the Golgi (anterograde). These coat proteins help vesicles form, protect their contents, and direct them to the correct cellular location.
  • How do SNARE proteins ensure specificity and facilitate membrane fusion during vesicle transport?
    SNARE proteins ensure specificity by having v-SNAREs on vesicles and t-SNAREs on target membranes; only matching pairs interact. When they bind, they form a tight four-helix bundle that brings the vesicle and target membranes close together, catalyzing membrane fusion. After fusion, NSF uses ATP hydrolysis to disassemble the SNARE complex.
  • What is the role of GTPases, particularly RAB proteins, in vesicle formation and targeting?
    GTPases like RAB proteins regulate the recruitment of coat proteins to vesicles, ensuring that the correct coat is assembled for each transport step. They control the specificity of vesicle targeting by recruiting specific coat proteins and helping direct vesicles to their proper destinations.
  • Describe the process by which clathrin-coated vesicles are formed and released from the membrane.
    Clathrin-coated vesicle formation begins when cargo binds to cargo receptors, which then bind adapter proteins. Clathrin binds to these adapters, forming a protein coat that shapes the vesicle. Dynamin, a GTPase, forms a ring around the neck of the budding vesicle and uses GTP hydrolysis to pinch it off from the membrane, releasing the vesicle.
  • What are the two main pathways of vesicle transport in the cell and what is their general direction?
    The secretory pathway moves molecules from the ER through the Golgi to the cell surface (outward), while the endocytic pathway brings molecules into the cell from the plasma membrane to organelles (inward).
  • Name the three main types of vesicle coat proteins and describe the direction of transport each mediates.
    Clathrin mediates transport between the Golgi and plasma membrane, COPI mediates retrograde transport from the Golgi to the ER, and COPII mediates anterograde transport from the ER to the Golgi.
  • How do adapter proteins contribute to clathrin-coated vesicle formation?
    Adapter proteins bind both the clathrin coat and cargo receptors, linking clathrin to the specific molecules that need to be transported in the vesicle.
  • What is the role of dynamin in clathrin-coated vesicle formation?
    Dynamin forms a ring around the neck of the budding vesicle and uses GTP hydrolysis to pinch the vesicle off from the membrane, releasing it.
  • How do RAB GTPases regulate vesicle coat recruitment and specificity?
    RAB GTPases control which coat proteins are recruited to the vesicle, ensuring that the correct type of coat is assembled for each transport step and directing vesicles to their proper destinations.
  • How do SNARE proteins ensure specificity and facilitate membrane fusion during vesicle transport?
    v-SNAREs on vesicles bind specifically to matching t-SNAREs on target membranes, forming a tight four-helix bundle that brings membranes together for fusion; NSF and ATP hydrolysis then disassemble the SNARE complex after fusion.
  • Which organelle is primarily responsible for transporting proteins around the cell?
    Transport vesicles, which are small membrane-enclosed organelles, are primarily responsible for moving proteins and other molecules between organelles and the plasma membrane within the cell.
  • What structure is responsible for transporting proteins within a cell, and how does it function?
    Transport vesicles are responsible for moving proteins within a cell. They bud from organelles like the ER or Golgi, are coated with specific proteins (such as clathrin, COP1, or COP2) that help direct them to their target location, and use SNARE proteins to ensure fusion with the correct target membrane.