Question

Which protein modification does NOT take place in the ER lumen?

              A.           Polyubiquitylation

              B.           N-linked glycosylation

              C.           Cysteine bridge formation

              D.          chaperone-mediated folding

              E.           GPI anchoring

2.  Which of these Eukaryotic proteins is least likely to exhibit an ER import sequence during translation?

              A.           Glutathione

              B.           CFTR

              C.           Protein disulfide isomerase

              D.          Acetylcholine receptor

              E.           Na+-K+-ATPase

3.  Which function is NOT attributed correctly to either smooth ER (SER) or rough ER (RER)?

Cytosolic protein synthesis - SER

Incorporation of new lipids into membrane bilayer - SER

Transmembrane protein incorporation - RER

Soluble protein synthesis for secretion - RER

Hormone synthesis - SER

Answer 1

1. (A).

Reason: Polyubiquitylation prevents proteins from sliding back into the ER lumen.

2. (E).

3. Cytosolic protein synthesis - SER (Reason: Protein synthesis needs ribosomes on RER).