Two important observations were made in the experimental analysis of the inserti

Question

Two important observations were made in the experimental analysis of the insertion of secretory proteins into microsomes. A microsomal protein synthesized in vitro on soluble polyribosomes was subsequently combined with with preparation of [____] whose ribosomes had been removed. The in vitro synthesized protein [____] incorporated into the microsomes, and it was [____] to proteolysis by an experimentally applied protease. If the microsome preparation was present [____] of the microsomal protein, however, this protein [____] into the microsomes and was resistant to the protease, thus demonstrating a co-translational import of protein into the microsomes. Secondly, the imported protein was [____] than the protein encoded in the mRNA, leading to the conclusion that an N-terminal signal sequence was required for targeting to the endoplasmic reticulum and had been removed upon import.

(1) rough microsomes; was not; susceptible; during translation; was incorporated; slightly smaller

(2) microsomes; was rapidly; resistant; following translation; failed to be incorporated; shorter

(3) smooth microsomes; failed to be; susceptible; before translation; was not incorporated; much shorter

(4) ER membrane; was not; not susceptible; following translation; was inserted; slightly longer

(5) cell extract; was always; subject; during isolation; was extruded; shorter

Explanation / Answer

The option is 4.ER membrane; was not; not susceptible; following translation; was inserted; slightly longer

Two important observations were made in the experimental analysis of the insertion of secretory proteins into microsomes. A microsomal protein synthesized in vitro on soluble polyribosomes was subsequently combined with with preparation of [_ER membrane___] whose ribosomes had been removed. The in vitro synthesized protein [__was not__] incorporated into the microsomes, and it was [___not susceptible_] to proteolysis by an experimentally applied protease. If the microsome preparation was present [__following translation__] of the microsomal protein, however, this protein [__was inserted__] into the microsomes and was resistant to the protease, thus demonstrating a co-translational import of protein into the microsomes. Secondly, the imported protein was [_slightly longer___] than the protein encoded in the mRNA, leading to the conclusion that an N-terminal signal sequence was required for targeting to the endoplasmic reticulum and had been removed upon import.

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