Edit the following statements, if required, to make it true: Because nuclear localization sequences are not cleaved off by proteases following protein import into the nucleus, they can be reused to import nuclear proteins after mitosis, when cytosolic and nuclear proteins have become intermixed due to nuclear envelope breakdown. This is in contrast to ER signal sequences, which are cleaved off by a signal peptidase once they reach the lumen of the ER. ER signal sequences cannot therefore be reused to import ER proteins after mitosis, when cytosolic and ER proteins have become intermixed; these ER proteins must therefore be degraded and resynthesized.

Question

Biology

Josephine Mcdonald

5 April, 01:56

Edit the following statements, if required, to make it true: Because nuclear localization sequences are not cleaved off by proteases following protein import into the nucleus, they can be reused to import nuclear proteins after mitosis, when cytosolic and nuclear proteins have become intermixed due to nuclear envelope breakdown. This is in contrast to ER signal sequences, which are cleaved off by a signal peptidase once they reach the lumen of the ER. ER signal sequences cannot therefore be reused to import ER proteins after mitosis, when cytosolic and ER proteins have become intermixed; these ER proteins must therefore be degraded and resynthesized.

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Asa Walter · Answer 1

The third sentence is not correct. The correct statement would be as follows:

because the contents of the lumen of ER (or any other compartment) in the secretory or endocytic pathways never mix with the cytosol, Proteins that enter these pathways is never imported again.

Explanation:

During mitosis, specifically during prophase, when the nuclear envelope breaks down, or in other words, retracts from the chromatin, its content that is the membrane protein intermix with the ER membrane protein. However its content will always remain separated from that of the cytosol because of the presence of an intact membrane.