Paper 2 · Proteins and Amino Acids
Which feature is characteristic of the globular structure of haemoglobin?
AHydrophilic R-groups face outward, making the molecule soluble in the cytoplasm.
BHydrophobic R-groups face outward, making the molecule soluble in the cytoplasm.
CAll R-groups are hydrophilic, making the molecule insoluble in water.
DThe polypeptide chains remain fully extended in a straight line to maximise surface area.
Explanation: In a globular protein such as haemoglobin, the polypeptide chains fold so that hydrophilic R-groups face outward into the surrounding aqueous cytoplasm, keeping the molecule soluble, while hydrophobic R-groups are tucked into the interior; this compact folded shape is the opposite of the extended, insoluble arrangement seen in fibrous structural proteins.
Derived from ZIMSEC Biology Paper 2, November 2004, Q6
