Question

Which of the following statements about the role of the COPI or COPII proteins in vesicular transport is CORRECT? They pinch and fuse the membrane to allow separation of the vesicle from the rest of the membrane of the donor compartment. They increase the curvature of the membrane and form the vesicle from the donor compartment. They bind to the membrane of the target organelle/compartment to ensure delivery specificity. They regulate the fusion of the vesicle membrane with its target membrane. Correct protein folding in the endoplasmic reticulum (ER) is essential for the function of proteins that are exported from the ER. The role of Calnexin in this process is to: (Choose the single CORRECT response). Add a complex sugar group (glucose, mannose, N-acetylglucosamine) to an Asn residue in the nascent peptide as it emerges into the lumen from the ER translocator. Removes the terminal glucose from the precursor oligosaccharide on unfolded peptide chains. Target misofolded proteins to the proteasome via an export translocation in the ER membrane. Bind to a single terminal glucose on the precursor oligosaccharide on unfolded peptide after glucose trimming and assist folding of the peptide.

Answer 1

Q4: Option 1 is correct.

Vesicular transport model postulates a stable stack of cisternae containing a fixed and ordered array of processing enzymes.The cargo is delivered to each cisterna in turn by vesicles that bud from one cisterna and fuse with the next in the stack.In this case COPI coated vesicles carry cargo and move in an anterograde or forward direction from one golgi cisterna to the next.The transport vesicles once laoded with the material (derived from donor compartment)   pinch off from its membrane and then they allow their cargo into a next compartment. This delivery is acheived by by fusing with that compartment .Proteins from Endoplasmic reticulum to golgi get transferred in this manner. Here. the transported proteins do not cross a membrane, so this transport moves proteins only between topologically equivalent compartments.

Q5: CORRECT OPTION IS 4

Calnexin is a calcium binding lectin and binds selectively to certain N-linked oligosaccharides on growing nascent chains.it recognizes N-linked oligosaccharides that contain a single terminal glucose, and therefore bind only after two of the three glucoses that are initially attached have been removed by ER glucosidases.When the third glucose, is removed, the protein dissociates from the chaperone and can leave ER. Thus,binding of calnexin to oligosaccaride on incompletely folded proteins helps it in retaining in ER.