Question

Predict the membrane orientation of a protein that is synthesized with an uncleaved, internal signal sequence, but does not contain a stop-transfer sequence. diagram the final orientation below, and show the n- and c- terminus of the protein relative to the cytosolic and luminal space of the er membrane. also show any transmembrane segments with correct orientation of either cytoplasmic or luminal loops.

Answer 1

If a protein is synthesized with an uncleaved, internal signal sequence but does not contain a stop-transfer sequence, it will end up with its N-terminus exposed to the cytosolic side of the ER membrane and its C-terminus exposed to the luminal space of the ER.

Step-by-step explanation:

In this case, since the protein does not contain a stop-transfer sequence, it will not be trapped in the fatty acid interior of the membrane. Therefore, the protein will continue to move through the RER membrane until it reaches the luminal space of the ER.

Its N-terminus, which is the end of the protein where the signal sequence is located, will be exposed to the cytosolic side of the ER membrane, while the C-terminus will be exposed to the luminal space of the ER. Since there is no stop-transfer sequence, the protein will not span the membrane and will not have any transmembrane segments. Instead, it will have cytoplasmic and luminal loops depending on the orientation of different regions of the protein relative to the ER membrane.