Question

Generally describe the mechanisms via which cells deal with misfolded proteins discussing the potential fates these proteins

Explain how transmembrane proteins are inserted into the membrane.

How is the transmembrane segment inserted into the membrane

Compare the 2 mechanisms via which you can get a single-pass protein inserted into the membrane

Explain how multi-pass transmembrane proteins would differ from single-pass transmembrane proteins in terms of the location and number of star- and stop-transfer sequences

Discuss the path taken by secreted proteins as well as by soluble proteins that are not destined for secretion, and explain the general characteristics that allow proteins to be targeted to a specific organelle.

Answer 1

Misfolded protein can induce cellular stress which overloads the proteolytic machinery. Cell produces chaperones which promote refolding of the misfolded protein, help in their degradation through the ubiquitin-proteasome pathway.

Tansmembrane proteins moves out of the translocon into the phospholipid bilayer. It is here that it anchors the protein.  The first α-helical segment initiates insertion of the growing chain into the ER membrane.

In single-pass transmembrane proteins, the crossing of polypeptide occurs only once crosses only once as opposed to multipass transmembrane proteins, where the polypeptide chain crosses multiple times. The insertion can be done through internal uncleaved signal-anchor sequence located near the N-terminus.