You isolate the rough ER from the cytoplasm and purify the mRNAs attached to it.

Question

You isolate the rough ER from the cytoplasm and purify the mRNAs attached to it. Circle any of the proteins you would expect such mRNA to encode; explain why the others are not expected on the ER. a. soluble secreted proteins b. ER trans-membrane proteins c. integral plasma membrane proteins d. endosomal/lysosomal proteins e. nuclear proteins f. SRP-receptor proteins g. 7SLRNA-associated-proteins Explain what would happen in each case below; assume that each of these proteins is NOT a membrane protein. Write answers on the back of this paper. A. You add a signal sequence (for the ER) to the N-terminus of a normally nuclear protein. B. You change the hydrophobic amino acids in an ER signal sequence into polar amino acids. C. You change the hydrophobic amino acids in an ER signal sequence into other hydrophobic amino acids. D. You add a N-terminal ER signal sequence to the C-terminal end of a normally cytoplasmic protein.

Explanation / Answer

The following proteins could be expected from the mRNA discussed in the question.

a. Soluble secreted proteins

b. ER trans-membrane proteins

c. Integral plasma membrane proteins

d. Endosomal/lysosomal proteins

e. SRP-receptor proteins

f. 7SL RNA proteins

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