Which choice is considered an integral membrane protein?
a. a protein capable of diffusing throughout the cytoplasm of a cell
b. a protein attached to a transmembrane protein via hydrogen bonding
c. a protein with its amino-terminus in the cytoplasm and its carboxy-terminus in the extracellular space
d. a protein attached to a phospholipid via ionic bonding with the head group of the lipid molecule

A protein with its amino-terminus in the cytoplasm and its carboxy-terminus in the extracellular space. (Ans. A)

Explanation:

Integral membrane protein (IMP) is defined as a membrane protein molecule which is directly attached to the biological membrane known as phospholipid bilayers. All transmembrane proteins are integral membrane protein but not all integral membrane protein are transmembrane proteins.

Integral membrane proteins function as a transporter, receptors, channels, proteins which is responsible for cell adhesion, proteins are also Involved in transduction and build up of energy.

Membrane proteins are class according to their transmembrane domain properties. The N-terminus of an integral membrane protein type I is in the endoplasmic reticulum lumen, where N-terminus of an integral membrane protein type II in the cytoplasm.