Question 2
Where are the carbohydrate portions of glycolipids and glycoproteins located in cell surface membranes?
Options:
A) The inside and outside surfaces of the membrane
B) The inside surface of the membrane
C) The interior of the membrane
D) The outside surface of the membrane
Answer:
Correct Answer: D) The outside surface of the membrane
Explanation:
Carbohydrate portions extend outward from the membrane surface, not within the membrane interior.
Location and Role of Carbohydrates on Glycolipids and Glycoproteins
Glycolipids and glycoproteins are molecules in the cell membrane with carbohydrate chains attached.
The carbohydrate portions are always located on the extracellular side (outside) of the membrane.
This orientation is essential for cell-cell communication, recognition, and signaling.
Why the Carbohydrate Chains Are on the Outside
The outer location of these carbohydrates allows them to interact with other cells and molecules in the extracellular environment.
Functions include:
Recognition by immune cells.
Attachment for other cells or signaling molecules.
Protection of the cell surface by forming a “glycocalyx,” a protective carbohydrate-rich layer.
Why Other Options Are Incorrect
A) Inside and Outside Surfaces
Carbohydrate chains are found only on the outside of the cell membrane, not on both sides.
B) Inside Surface of the Membrane
Carbohydrate chains do not face the cytoplasmic (inner) side of the cell membrane.
C) Interior of the Membrane
The hydrophobic interior of the membrane bilayer is unsuitable for carbohydrate chains, which are hydrophilic.