When a Nutrient Moves With the Help of a Carrier

When a nutrient moves with the help a carrier, the process is called active transport. The substance moves across the cell membrane in a gradient of concentration. In the process, the carrier accumulates molecules in high concentrations that the cell requires for its metabolism. This type of transport uses free energy produced by inorganic ions to move the solute. A carrier protein can also transport molecules and ions passively through secondary active transport. In both cases, the carrier protein is necessary to move particles from low concentration to high concentration.

Transport proteins are found in the plasma membrane. They are nonuniformly distributed across the cell membrane and contribute to the transcellular transport of absorbed solutes. Among them are Na+-linked symporters, which actively transport nutrients into cells. On the other hand, Na+-independent transport proteins, which are found in the basal and lateral domains of the plasma membrane, allow nutrients to leave the cell passively down concentration gradients.

Passive diffusion of nutrients through cells occurs when a carrier protein binds to a nutrient and moves it from one side of the membrane to the other. Facilitated diffusion is similar to passive diffusion except that the carrier protein assists the nutrient in moving from one side to the other of the membrane without using energy. This type of membrane transport is the most popular and includes both passive and active modes of transport.

Carrier proteins act like enzymes in that they transport a specific solute across the cell membrane. They change their shape and the solute binds with its binding site. Once the solute binds to its binding site, the carrier proteins catches the substrate within the molecular structure. Once the substrate reaches its binding site, it’s released from the carrier protein onto the cell’s surface.

When a Nutrient Moves With the Help of a Carrier
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