Question

DNA cannot pass through a cell membrane as
A. It is too big to cross the membrane
B. It is a hydrophilic molecule
C. Membrane does not have specific proteins to facilitate the transport
D. None of these

Answer 1

Cell membrane or plasma membrane is a selectively semi-permeable membrane that allows some selective passage of molecules across it. DNA is a negatively charged molecule that cannot pass through the cell membrane because of its structural components.

Complete answer:
The cell membrane is the semi-permeable membrane that encloses the cytoplasm and membrane-bound organelles. It consists of a thin layer of amphipathic phospholipids that are arranged so that the hydrophobic tail regions are isolated from the surrounding environment whereas the hydrophilic head regions interact with the cytosolic and external environment. The plasma membrane allows a variety of molecules to pass through, such as small non-polar molecules (oxygen and carbon dioxide), small uncharged polar molecules (water), but some large uncharged molecules (glucose) cannot pass through it. Some hydrophilic charged molecules such as DNA also cannot pass through the cell membrane because the cell membrane is made up of lipid bilayer which is hydrophobic in nature.
Hence, the correct option is (B)-It is a hydrophilic molecule.

Note: Some charged molecules such as deoxyribonucleic acids (DNA) cannot pass through the cell membrane regardless of their size. DNA is a water-loving or hydrophilic molecule like the exterior of the cell membrane and therefore, it cannot pass through the phospholipid bilayer.