Question

The movement of a single molecule across a membrane by carrier protein is called

• A. symport
• B. uniport
• C. antiport
• D. all of these

Answer 1

The correct option is B uniport

Uniport, symport and antiport are types of facilitated diffusion. In facilitated diffusion, the molecules move from a region of their higher concentration to a region of their lower concentration facilitated by proteins. The proteins are of two types: the channel proteins and the carrier proteins. Channel proteins form pores in the membrane through which the substances get transported. The carrier proteins bind to molecules that need to be transported and undergo changes in their structure so as to move the molecules on to the other side of the membrane.

In uniport, carrier protein binds to one specific molecule and transports it across the membrane. Hence, the movement of one molecule is independent of the movement of other molecules.
In symport, the carrier proteins transport two molecules across the membrane in the same direction. In antiport, the carrier proteins transport two molecules across the membrane in opposite directions. Unlike uniport, in symport and antiport, the carrier proteins cause the movement of two molecules simultaneously.