Anonymous
Apr 22
Describe protein uptake to ER in detail?
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Apr 22
Protein uptake to the endoplasmic reticulum (ER) is a complex process that involves multiple steps and molecular interactions. Here is a detailed description of how proteins are transported to the ER:
1. Synthesis of proteins: Proteins that are destined for the ER are synthesized on ribosomes bound to the rough endoplasmic reticulum (RER). These proteins contain a signal sequence, also known as a signal peptide, at their N-terminus. The signal sequence is recognized by a signal recognition particle (SRP), which binds to the ribosome and halts protein synthesis.
2. Targeting to the ER: The SRP-ribosome complex is then targeted to the ER membrane, where it interacts with the SRP receptor. This interaction leads to the transfer of the ribosome to the translocon, a protein channel in the ER membrane.
3. Translocation into the ER lumen: The signal sequence of the protein is inserted into the translocon, and the protein is translocated across the ER membrane into the ER lumen. This process is facilitated by the translocon complex, which acts as a protein-conducting channel.
4. Protein folding and modification: Once inside the ER lumen, the protein undergoes folding and post-translational modifications, such as glycosylation and disulfide bond formation. Chaperone proteins help in the folding process and ensure that the protein attains its correct conformation.
5. Quality control: The ER has a quality control system that monitors the folding and assembly of proteins. Misfolded or unassembled proteins are targeted for degradation by the ER-associated degradation (ERAD) pathway.
6. Transport to other organelles: Proteins that are correctly folded and assembled in the ER may be further transported to other organelles, such as the Golgi apparatus, lysosomes, or plasma membrane, for their specific functions.
In summary, protein uptake to the ER involves the recognition of a signal sequence, targeting to the ER membrane, translocation across the membrane, folding and modification, quality control, and further transport to other organelles. This process ensures that proteins are properly synthesized and processed before they are sent to their final destination within the cell.
1. Synthesis of proteins: Proteins that are destined for the ER are synthesized on ribosomes bound to the rough endoplasmic reticulum (RER). These proteins contain a signal sequence, also known as a signal peptide, at their N-terminus. The signal sequence is recognized by a signal recognition particle (SRP), which binds to the ribosome and halts protein synthesis.
2. Targeting to the ER: The SRP-ribosome complex is then targeted to the ER membrane, where it interacts with the SRP receptor. This interaction leads to the transfer of the ribosome to the translocon, a protein channel in the ER membrane.
3. Translocation into the ER lumen: The signal sequence of the protein is inserted into the translocon, and the protein is translocated across the ER membrane into the ER lumen. This process is facilitated by the translocon complex, which acts as a protein-conducting channel.
4. Protein folding and modification: Once inside the ER lumen, the protein undergoes folding and post-translational modifications, such as glycosylation and disulfide bond formation. Chaperone proteins help in the folding process and ensure that the protein attains its correct conformation.
5. Quality control: The ER has a quality control system that monitors the folding and assembly of proteins. Misfolded or unassembled proteins are targeted for degradation by the ER-associated degradation (ERAD) pathway.
6. Transport to other organelles: Proteins that are correctly folded and assembled in the ER may be further transported to other organelles, such as the Golgi apparatus, lysosomes, or plasma membrane, for their specific functions.
In summary, protein uptake to the ER involves the recognition of a signal sequence, targeting to the ER membrane, translocation across the membrane, folding and modification, quality control, and further transport to other organelles. This process ensures that proteins are properly synthesized and processed before they are sent to their final destination within the cell.
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Google Gemini AI
Apr 22
Protein Uptake to the Endoplasmic Reticulum (ER)
1. Translation and Co-translational Import:
- Ribosomes translate mRNA into nascent polypeptide chains, which emerge from the ribosome on the cytosolic side.
- Ribosome-bound proteins (RBPs), such as the signal recognition particle (SRP), bind to exposed hydrophobic signal sequences within the nascent chain.
2. SRP Recognition and Binding:
- The SRP recognizes the signal sequence and binds to it, forming the SRP-ribosome-nascent chain complex.
- The SRP chaperone prevents the hydrophobic signal sequence from interacting with the cytosolic environment.
3. Transport to ER:
- The SRP-complex binds to the SRP receptor (SR) on the ER membrane.
- The binding triggers the translocation of the nascent chain across the ER membrane through the translocation通道。
4. Translocation and Integration:
- The translocon complex, consisting of the Sec61 channel and other proteins, facilitates the translocation of the nascent chain into the ER lumen.
- Hydrophobic portions of the protein are integrated into the lipid bilayer, while hydrophilic portions remain in the lumen.
- The ER chaperones bind to the nascent chain to prevent misfolding and aggregation.
5. Release of SRP and Ribosome:
- Once translocation is complete, the SRP is released and leaves the ER membrane.
- The ribosome detaches from the translocon and re-enters the cytosol to continue translation.
Additional Mechanisms:
- Co-translational translocation: The nascent chain is translocated into the ER while translation is still ongoing.
- Post-translational translocation: Completed proteins that lack an N-terminal signal sequence can be translocated into the ER via other mechanisms, such as the ER-associated degradation (ERAD) pathway.
- Unfolded protein response (UPR): When ER protein folding is impaired, the ER undergoes a stress response that triggers increased protein folding capacity and degradation of misfolded proteins.
1. Translation and Co-translational Import:
- Ribosomes translate mRNA into nascent polypeptide chains, which emerge from the ribosome on the cytosolic side.
- Ribosome-bound proteins (RBPs), such as the signal recognition particle (SRP), bind to exposed hydrophobic signal sequences within the nascent chain.
2. SRP Recognition and Binding:
- The SRP recognizes the signal sequence and binds to it, forming the SRP-ribosome-nascent chain complex.
- The SRP chaperone prevents the hydrophobic signal sequence from interacting with the cytosolic environment.
3. Transport to ER:
- The SRP-complex binds to the SRP receptor (SR) on the ER membrane.
- The binding triggers the translocation of the nascent chain across the ER membrane through the translocation通道。
4. Translocation and Integration:
- The translocon complex, consisting of the Sec61 channel and other proteins, facilitates the translocation of the nascent chain into the ER lumen.
- Hydrophobic portions of the protein are integrated into the lipid bilayer, while hydrophilic portions remain in the lumen.
- The ER chaperones bind to the nascent chain to prevent misfolding and aggregation.
5. Release of SRP and Ribosome:
- Once translocation is complete, the SRP is released and leaves the ER membrane.
- The ribosome detaches from the translocon and re-enters the cytosol to continue translation.
Additional Mechanisms:
- Co-translational translocation: The nascent chain is translocated into the ER while translation is still ongoing.
- Post-translational translocation: Completed proteins that lack an N-terminal signal sequence can be translocated into the ER via other mechanisms, such as the ER-associated degradation (ERAD) pathway.
- Unfolded protein response (UPR): When ER protein folding is impaired, the ER undergoes a stress response that triggers increased protein folding capacity and degradation of misfolded proteins.
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