Question

Specific proteins responsible for the flow of materials and information into the cell are called
A. Membrane receptors
B. Carrier proteins
C. Integral proteins
D. None of these

Answer 1

Hint: Membrane transport is of two types: Active transport and Passive transport. Active transport is the uphill movement that is the substances are transported across the membrane against the electron-chemical gradient or the concentration gradient means the molecules will move from lower concentration to the higher concentration.

Complete answer:
For active transport, special organic molecules called the carrier proteins are required. For each solute particle, a special carrier protein is needed. These carrier proteins bind with the solute particles thus making carrier solute complex. The binding sites for this carrier molecule are present on both the sides of the membrane. The formation of carrier solute complexes is often associated with the conformational changes in the solute particles which help in the transport of solute particles from one side of membrane to the other side. As this transport is against the concentration gradient, it requires energy in the form of ATP. This energy aids in bringing the conformational changes in the carrier molecule.

Hence, the correct answer is option (B).

Note: The specific binding sites present on the carrier proteins for binding the substrate or solute particles can be one or more. This helps in transport of the solute particles across the lipid bilayer through conformational changes that are reversible. The transport across the membrane is maximal when all the sites present on carrier molecules for solute binding are occupied, that is the carrier is fully saturated.