18 Questions
What is the primary function of the rough endoplasmic reticulum (RER) in protein synthesis?
The synthesis of proteins destined for the endomembrane system or export
What is the role of the smooth endoplasmic reticulum (SER) in lipid metabolism?
The synthesis of cholesterol and steroid hormones, as well as the detoxification of foreign substances
What is the site of production of most lipid classes in the cell?
The ER membrane
What is the mechanism by which proteins are translocated into the endoplasmic reticulum during co-translational import?
The signal sequence and protein translocators
What is the role of Ran-GTP in protein transport in the cell?
Mediating the transport of proteins into the nucleus
What is the destination of proteins synthesized on ribosomes attached to the endoplasmic reticulum?
The endomembrane system or export
What is the primary function of the endoplasmic reticulum (ER) in protein synthesis?
The primary function of the ER is the synthesis of proteins and lipids.
What is the role of the N-terminal ER signal sequence on a polypeptide?
The N-terminal ER signal sequence on a polypeptide means it will be bound for the RER (co-translational translocation).
What happens to most polypeptides in the ER lumen?
Most polypeptides are modified in the ER lumen.
What is the role of the Golgi apparatus in protein synthesis?
Further processing of proteins occurs as they move along the vesicle transport pathway through the Golgi.
What is the final destination of proteins that are not retained in the ER lumen or become integral membrane proteins?
Proteins can be packaged into secretory vesicles or lysosomes.
How do proteins in the ER lumen get secreted from the cell or travel to lysosomes?
Proteins in the ER lumen can be secreted from the cell through secretory vesicles or travel to lysosomes through the vesicle transport pathway.
What is the process by which multiple ribosomes translate a single mRNA molecule simultaneously, and how far apart are they spaced?
Polysomes or polyribosomes occur when multiple ribosomes, spaced 80-100 nucleotides apart, translate protein simultaneously on a single mRNA molecule.
What are the two distinct mechanisms of protein importation into organelles, and when do they occur?
The two mechanisms are post-translational import and co-translational import. Post-translational import occurs after protein synthesis, while co-translational import occurs during protein synthesis.
What is the role of the Sec62 and Sec63 complex in protein importation into the ER, and how does it facilitate the process?
The Sec62 and Sec63 complex positions Bip molecules to bind the polypeptide in the ER lumen, assisting in the translocation of the polypeptide across the membrane.
What is the mechanism by which the growing polypeptide chain is threaded across the ER membrane during co-translational import, and what is required for this process?
The growing polypeptide chain is threaded across the membrane as it is made, and no additional energy is required, as the only path available to the growing chain is to cross the membrane.
What is the role of Hsp70 chaperones and Bip molecules in protein translocation into the ER, and how do they interact with the polypeptide?
Hsp70 chaperones bind to the polypeptide and detach as it is passed through the membrane, while Bip molecules bind to the polypeptide in the ER lumen and assist in pulling it into the ER using a ratchet-like mechanism.
In which cellular compartment can ribosomes be found, and how are they anchored to the ER membrane during protein synthesis?
Ribosomes can be found free in the cytosol or attached to the ER. During protein synthesis, they are anchored to the ER membrane through the interaction with the Sec61 translocator.
Test your knowledge on the endoplasmic reticulum, protein synthesis, and vesicular transport with this quiz covering chapters 12, 16, and 19 of Molecular Biology of the Cell, 7th edition. Learn about the differences between SER and RER, co-translational import of proteins, and more cellular processes.
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