For a protein to enter the endoplasmic reticulum as part of the endoplasmic reticulum's lumen or part of the endoplasmic reticulum's membrane:
a. The messenger RNA goes directly to the ER.
b. A ribosome binds to the mRNA and a short stretch of protein is synthesized that contains a signal sequence.
c. Ribosomes at the endoplasmic reticulum bind to the protein
d. Is a random event and one day the protein could go to the ER and on another day the same protein could associate with a free polyribosome.
e. None of the above.
Answer: b. A ribosome binds to the mRNA and a short stretch of protein is synthesized that contains a signal sequence.
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