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Multiple Choice
Cells are able to distinguish proteins destined for secretion or for segregation to specific intracellular compartments from those that will remain in the cytoplasm because __________.
A
there are two types of ribosomes: one group that synthesizes cytoplasmic proteins only and another type that synthesizes secreted or compartment-specific proteins only
B
proteins destined for secretion or for a specific compartment are all synthesized in the nucleus, whereas cytoplasmic proteins are all synthesized in the cytoplasm
C
each compartment in the cell (the nucleus, lysosome, and so forth) has its own set of ribosomes that synthesize proteins unique to that compartment
D
some proteins, as they begin to be synthesized, contain a signal region that causes the ribosome with its growing polypeptide to attach to the ER and translocate the polypeptide into the lumen (space) of the ER
Verified step by step guidance
1
Understand that proteins destined for secretion or specific compartments have a signal sequence that directs their synthesis.
Recognize that this signal sequence is a short peptide that emerges from the ribosome during translation.
Learn that the signal sequence is recognized by a signal recognition particle (SRP), which halts translation temporarily.
Know that the SRP-ribosome complex then binds to a receptor on the endoplasmic reticulum (ER) membrane.
Realize that once bound to the ER, translation resumes, and the growing polypeptide is translocated into the ER lumen.