Question

Which is not an example of transmembrane transport between different subcellular compartments?

• A. Transport from the stroma into thylakoid space
• B. Transport from the cytoplasm into the lumen of the endoplasmic reticulum
• C. Transport from the endoplasmic reticulum into the Golgi complex
• D. Transport from mitochondrial intermembrane space into the mitochondrial matrix

Hint:

ER $\rightarrow$ Golgi transport occurs by \textbf{vesicles}, not by direct transmembrane movement.

Answer 1

The Correct Option is C

Step 1: Transmembrane transport involves movement of molecules across a biological membrane through protein channels or transporters.
Step 2:

(A) Stroma $\rightarrow$ thylakoid space involves transport across the thylakoid membrane.
(B) Cytoplasm $\rightarrow$ ER lumen involves transport across the ER membrane via translocons.
(D) Intermembrane space $\rightarrow$ mitochondrial matrix involves transport across the inner mitochondrial membrane.

Step 3: Transport from ER to Golgi does not occur by crossing a membrane directly. Instead, proteins are moved via vesicular transport, where membrane-bound vesicles bud off from the ER and fuse with the Golgi.
Step 4: Since vesicular transport does not involve passage through a membrane, it is not transmembrane transport.