Question

Which is true of water-soluble proteins transferred from the cytosol to the ER?

Choose one:
A. In most cases, their signal sequence remains attached to the C-terminus.
B. They are often destined for secretion.
C. They do not require an ER signal sequence.
D. In most cases, their signal sequence remains attached to the N-terminus.
E. They must fold properly to be able to enter the ER.

Answer 1

The true statement is that water-soluble proteins transferred from the cytosol to the ER are often destined for secretion. These proteins have an ER signal sequence typically at the N-terminus that is cleaved off after the protein enters the ER.

Step-by-step explanation:

The correct answer to the question is 'B. They are often destined for secretion.' When water-soluble proteins are transferred from the cytosol to the endoplasmic reticulum (ER), they are usually destined to be secreted from the cell or inserted into a membrane. The synthesis of these proteins begins with the recognition of an ER signal sequence, often located at the N-terminus of the polypeptide chain. This sequence is recognized by a signal recognition particle that directs the ribosome to the ER membrane where the synthesis of the protein continues.

Once the polypeptide enters the ER, the signal sequence is typically cleaved off. The protein can then undergo further modifications, such as folding and the addition of carbohydrates, as it moves through the ER and Golgi apparatus, eventually leading to its secretion or incorporation into the plasma membrane.