When translating secretory or membrane proteins, ribosomes are directed to the ermembrane bya) a specific characteristic of the ribosome itself, which distinguishes free ribosomes from boundribosomes. b) a signal-recognition particle that brings ribosomes to a receptor protein in the er membrane. c) moving through a specialized channel of the nucleus. d) a chemical signal given off by the er. e) a signal sequence of rna that precedes the start codon of the message. b

B) a signal-recognition particle that brings ribosomes to a receptor protein in the ER membrane.

Explanation:

Each synthesized protein has to be targeted to the specific location and transported to that location. There are two possible ways for that transport: post-translational transport or co-translational transport.

•Co-translational transport occurs during the process of translation, and proteins transported this way are proteins bound for organelles in the endomembrane system (such as the ER, Golgi apparatus, and lysosome), plasma membrane proteins or proteins for the exterior of the cell. They have an amino sequence called a signal peptide which sends them to ER first.

•Proteins that do not have a signal peptide stay in the cytosol so, their transport is after the translation (post-translational).

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