Protein Cotranslational Targeting to the ER
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Questions and Answers

What is the final product of the conversion of diacylglycerol to phosphatidylcholine?

  • Phosphatidic acid
  • Phosphocholine (correct)
  • Phospholipid flippase
  • Phosphatase

Where are phospholipids synthesized in relation to the ER membrane?

  • On the luminal side of the ER membrane
  • In the Golgi apparatus
  • On both sides of the ER membrane simultaneously
  • On the cytosolic side of the ER membrane (correct)

What facilitates the transfer of phospholipids to the lumenal half of the ER bilayer?

  • Flippases (correct)
  • Mitochondria
  • Ribosomes
  • Golgi apparatus

Where are large amounts of smooth ER typically found?

<p>Steroid-producing cells (D)</p> Signup and view all the answers

What is the primary function of smooth ER in the liver?

<p>Detoxification of compounds (D)</p> Signup and view all the answers

Which process occurs at the smooth ER?

<p>Synthesis of steroid hormones (B)</p> Signup and view all the answers

What is the role of the signal recognition particle (SRP) in cotranslational targeting of secretory proteins to the ER?

<p>Binds to the signal sequence emerging from the ribosome (D)</p> Signup and view all the answers

What happens after the signal recognition particle (SRP) escorts the complex to the ER membrane?

<p>The SRP binds to the translocon (B)</p> Signup and view all the answers

Which step involves the insertion of the signal sequence into the translocon during cotranslational targeting of secretory proteins to the ER?

<p>Step 3: Release of SRP and ribosome binding to translocon (D)</p> Signup and view all the answers

What drives the translocation of the growing polypeptide chain across the membrane during cotranslational targeting to the ER?

<p>Continued translation process (C)</p> Signup and view all the answers

Which enzyme is responsible for cleaving the signal sequence during cotranslational targeting of secretory proteins to the ER?

<p>Signal peptidase (C)</p> Signup and view all the answers

Where are glycolipids and sphingomyelin synthesized?

<p>Golgi apparatus (D)</p> Signup and view all the answers

How are proteins transported from the Golgi apparatus to their final destinations?

<p>In vesicles (A)</p> Signup and view all the answers

What is one function of the Golgi apparatus besides processing glycoproteins?

<p>Synthesizing glycolipids (A)</p> Signup and view all the answers

Where are ceramide, cholesterol, and glycerol phospholipids synthesized?

<p>Endoplasmic Reticulum (D)</p> Signup and view all the answers

What is the process known as when proteins are targeted to late endosomes that develop into lysosomes?

<p>Autophagy (B)</p> Signup and view all the answers

In polarized epithelial cells, how are plasma membranes divided?

<p>Apical and basolateral domains (D)</p> Signup and view all the answers

What is the role of Arf/GTP in vesicle formation?

<p>Recruits an adaptor protein for cargo selection and coat assembly (C)</p> Signup and view all the answers

Where are lysosomes formed?

<p>From late endosomes and transport vesicles (C)</p> Signup and view all the answers

What happens when Dynamin constricts the neck of a vesicle?

<p>Membrane fission occurs (B)</p> Signup and view all the answers

What is one major function of lysosomes?

<p>Digesting material taken up by endocytosis (C)</p> Signup and view all the answers

Where are active drugs processed in the cell?

<p>Lysosomes (A)</p> Signup and view all the answers

What leads to the formation of lysosomes?

<p>Fusion of transport vesicles with trans-Golgi network (B)</p> Signup and view all the answers

What is the final destination for transmembrane proteins after they are inserted into the ER membrane?

<p>Golgi apparatus (A)</p> Signup and view all the answers

Where are the portions of polypeptide chains that are translocated into the ER exposed following transport to the plasma membrane?

<p>Cytosolic side (B)</p> Signup and view all the answers

How are membrane proteins with internal transmembrane sequences inserted in the ER membrane?

<p>Its amino (N) terminus is exposed on the cytosolic side (A)</p> Signup and view all the answers

Which region of a protein directs the insertion of a polypeptide chain into the ER membrane?

<p>20-25 hydrophobic amino acids (D)</p> Signup and view all the answers

What happens to a polypeptide chain after its transmembrane sequence exits the translocon during insertion into the ER membrane?

<p>It anchors in the lipid bilayer (A)</p> Signup and view all the answers

What is the topological equivalence between the lumens of the ER and Golgi apparatus?

<p>They are equivalent to the exterior of the cell (A)</p> Signup and view all the answers

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