Question

Why do KDEL receptors transport ER-resident proteins from Golgi back to the ER?

1) Because the concentration of ER-resident proteins is higher in the Golgi than in the ER.
2) Because the concentration of ER-resident proteins is higher in the ER than in the Golgi.
3) Because KDEL receptors have a higher affinity for ER-resident proteins in the Golgi.
4) Because KDEL receptors have a higher affinity for ER-resident proteins in the ER.

Answer 1

KDEL receptors transport ER-resident proteins back to the ER because they have a higher affinity for these proteins in the acidic environment of the Golgi, not in the ER. The correct answer is option 3.

Step-by-step explanation:

KDEL receptors are responsible for ensuring that ER-resident proteins which have mistakenly been transported to the Golgi apparatus are returned to the Endoplasmic Reticulum (ER). The retrograde transport of these proteins from the Golgi back to the ER occurs because KDEL receptors have a higher affinity for these proteins in the acidic environment of the Golgi apparatus.

The lowering of the pH in the Golgi enables the KDEL receptors to bind these proteins more tightly and transport them back to the ER where they are released upon reaching the more neutral pH environment. This mechanism ensures that ER resident proteins, which often play crucial roles within the ER, such as protein folding and quality control, are retained within the ER to carry out their functions.

The correct option for why KDEL receptors transport ER-resident proteins back to the ER is therefore option 3: 'Because KDEL receptors have a higher affinity for ER-resident proteins in the Golgi.'