Question

Differentiate between symport, antiport, and uniport.

Answer 1

In any organism, movement of solute is very controlled and is done by the help of proteins; these are differentiated on the basis of movement of direction of the proteins.

Complete answer:
Movement of certain solutes through the cell membrane cannot occur by the method of simple diffusion. For these molecules specialized protein channels are present on the cell membrane which facilitate their diffusion. This is known as facilitated diffusion. Some of these protein channels allow transport of two molecules or substances at a time and this is known as cotransport.

Three types of facilitated diffusion are seen:
Uniport: Movement of one molecule independent of the other molecules is known as a uniport.
Symport: Movement of two molecules in the same direction through a protein channel is known as symport.
Antiport: Movement of two molecules in the opposite direction through a protein channel is known as antiport.

Uniport	Symport	Antiport
A single molecule is transported	Two molecules are transported	Two molecules are transported
The direction of transport is either inside or outside	Two molecules transported in the same direction	Two molecules transported in the opposite direction
GLUT1 is a glucose transporter present in the membrane of erythrocytes. Helps in taking up glucose.	Sodium-glucose symport is present in the lining of the small intestine. Two sodium ions and one glucose molecule are transported into the enterocyte cells.	Sodium-calcium antiport is present in the cardiac muscle cells. Three sodium ions and one calcium ion are transported in the opposite direction.

Note: -All three types of transport, symport, antiport, and uniport are facilitated type diffusion.
-Facilitated diffusion has certain properties. Transmembrane protein channels are required, it is highly specific and selective, saturates with the rise in the number of solutes. But the diffusion is a downhill type, which means it occurs along the concentration gradient and not against the gradient. It is a passive type of transport and hence no energy is required.
-Diffusion is also a passive process and only downhill transport can take place by diffusion.
-Active transport requires ATP and specialized transmembrane proteins.

Facilitated diffusion and diffusion are both passive processes and show downhill transport of solutes, but in facilitated diffusion transmembrane protein channels are required, which is not so in the case of diffusion.