Molecular Biology of the Cell: Chapters 12, 16 and 19

The synthesis of proteins destined for the endomembrane system or export

The synthesis of cholesterol and steroid hormones, as well as the detoxification of foreign substances

The ER membrane

<p>The signal sequence and protein translocators</p> Signup and view all the answers

<p>Mediating the transport of proteins into the nucleus</p> Signup and view all the answers

<p>The endomembrane system or export</p> Signup and view all the answers

<p>The primary function of the ER is the synthesis of proteins and lipids.</p> Signup and view all the answers

<p>The N-terminal ER signal sequence on a polypeptide means it will be bound for the RER (co-translational translocation).</p> Signup and view all the answers

<p>Most polypeptides are modified in the ER lumen.</p> Signup and view all the answers

<p>Further processing of proteins occurs as they move along the vesicle transport pathway through the Golgi.</p> Signup and view all the answers

<p>Proteins can be packaged into secretory vesicles or lysosomes.</p> Signup and view all the answers

<p>Proteins in the ER lumen can be secreted from the cell through secretory vesicles or travel to lysosomes through the vesicle transport pathway.</p> Signup and view all the answers

<p>Polysomes or polyribosomes occur when multiple ribosomes, spaced 80-100 nucleotides apart, translate protein simultaneously on a single mRNA molecule.</p> Signup and view all the answers

<p>The two mechanisms are post-translational import and co-translational import. Post-translational import occurs after protein synthesis, while co-translational import occurs during protein synthesis.</p> Signup and view all the answers

<p>The Sec62 and Sec63 complex positions Bip molecules to bind the polypeptide in the ER lumen, assisting in the translocation of the polypeptide across the membrane.</p> Signup and view all the answers

<p>The growing polypeptide chain is threaded across the membrane as it is made, and no additional energy is required, as the only path available to the growing chain is to cross the membrane.</p> Signup and view all the answers

<p>Hsp70 chaperones bind to the polypeptide and detach as it is passed through the membrane, while Bip molecules bind to the polypeptide in the ER lumen and assist in pulling it into the ER using a ratchet-like mechanism.</p> Signup and view all the answers

<p>Ribosomes can be found free in the cytosol or attached to the ER. During protein synthesis, they are anchored to the ER membrane through the interaction with the Sec61 translocator.</p> Signup and view all the answers