What causes the cargo (or ligand) to be released from the receptor in the endosomes during receptor mediated endocytosis?
A. The primary structure has the necessary information for the release from receptor.
B. Lower pH in the endosomes cause disruption of interactions between the cargo (ligand) and the receptors.
C. The low pH in causes degradation of the receptors in the endosomes.
D. The low pH helps receptors to leave the membranes of the endosomes so they can be recycled back to the PM.
E. The cargo (ligand) forms aggregates with other cargo coming into the cell by endocytosis.
The correct answer and explanation is:
Correct Answer: B. Lower pH in the endosomes cause disruption of interactions between the cargo (ligand) and the receptors.
Receptor-mediated endocytosis is a cellular process that allows cells to internalize specific molecules such as nutrients, hormones, or proteins by recognizing them with surface receptors. After binding to their specific ligands on the cell surface, receptors cluster together and are engulfed into the cell in a vesicle. This vesicle eventually fuses with early endosomes.
Inside the endosome, the internal environment becomes more acidic as protons are pumped into the lumen by proton pumps. This acidification plays a critical role in the release of the cargo from the receptor. The key factor here is the lower pH, which changes the protonation state of both the receptor and the ligand. As the pH drops, the hydrogen bonding and ionic interactions between the receptor and the ligand are disrupted. This change weakens their binding affinity, causing the ligand to be released from the receptor.
The receptors, after releasing the ligand, are typically recycled back to the plasma membrane for reuse, while the cargo may be sent to lysosomes for degradation or further processing, depending on its function. This acid-driven dissociation ensures the specificity and efficiency of the endocytic recycling system.
Other choices are incorrect for the following reasons:
- A: The primary structure does not drive the ligand release mechanism.
- C: Receptors are not degraded in early endosomes simply due to low pH.
- D: Low pH does not cause receptors to leave the membrane; recycling involves vesicular transport, not membrane detachment due to pH.
- E: Ligands do not form aggregates as a mechanism for release.
Thus, the acidification of endosomes is the key mechanism for ligand release during receptor-mediated endocytosis.