Which of the following is not a type of intracellular vesicle transport?
A. Outward flow of a plasma membrane transmembrane protein
B. Transport of nuclear encoded mitochondrial proteins into the mitochondria
C. Transport of lysosomal proteins from the Golgi, mediated by the M6P receptor
D. Receptor-mediated endocytosis
E. None of the above (all are types of intravesicular trafficking) Notes:
The correct answer and explanation is:
The correct answer is E. None of the above (all are types of intravesicular trafficking).
Explanation:
Intracellular vesicle transport refers to the processes by which molecules and proteins are transported within the cell using membrane-bound vesicles. These processes are crucial for maintaining cellular function and organization. Here is a breakdown of each option:
- Outward flow of a plasma membrane transmembrane protein (A):
This refers to the process of exocytosis, where proteins or lipids, such as transmembrane proteins, are transported from the endoplasmic reticulum (ER) or Golgi apparatus to the plasma membrane. The transport happens via vesicles that bud off from the ER or Golgi, and these vesicles fuse with the plasma membrane, inserting the protein into the membrane. This is a form of intracellular vesicle trafficking. - Transport of nuclear-encoded mitochondrial proteins into the mitochondria (B):
The mitochondria import many of their proteins from the cytosol. The nuclear-encoded mitochondrial proteins are synthesized in the cytoplasm and then imported into the mitochondria through a process that involves specific transport proteins and receptors on the mitochondrial membrane. This process is distinct from traditional vesicular trafficking, but it still involves movement of proteins and is an essential type of intracellular transport. - Transport of lysosomal proteins from the Golgi, mediated by the M6P receptor (C):
This is a classic example of intravesicular trafficking. The mannose-6-phosphate (M6P) receptor in the Golgi recognizes lysosomal enzymes that have been tagged with M6P, which directs them into vesicles for transport to the lysosomes. This process ensures that enzymes are delivered to their correct destination within the cell. - Receptor-mediated endocytosis (D):
This is another example of vesicle-mediated transport. In receptor-mediated endocytosis, cells take up specific molecules from the extracellular fluid by forming vesicles at the plasma membrane. These vesicles engulf the target molecules, such as hormones or nutrients, which are then transported into the cell.
All of these processes are types of intracellular vesicular transport. Therefore, E. None of the above is the correct answer because all listed options are valid types of intracellular vesicle trafficking.