Definition of active transport

Photonics Dictionary

active transport: Active transport is a biological process by which cells move molecules or ions across their cell membrane against their concentration gradient, meaning from a region of lower concentration to a region of higher concentration. This process requires energy because it is working against the natural tendency of molecules to move from high to low concentration (passive transport). Here are key points about active transport:

Energy requirement: Active transport requires energy, typically in the form of adenosine triphosphate (ATP), to move substances against their concentration gradient.

Carrier proteins: Specialized proteins in the cell membrane, known as carrier proteins or pumps, facilitate active transport. These proteins bind to the molecules or ions to be transported and undergo a conformational change to move the substance across the membrane.

Types of active transport:

Primary active transport: Direct use of metabolic energy (e.g., ATP) to transport molecules. An example is the sodium-potassium pump (Na+/K+ pump) that maintains the electrochemical gradient in cells.

Secondary active transport (co-transport): Uses the energy stored in the form of an electrochemical gradient created by primary active transport. This can be further divided into symport (both substances move in the same direction) and antiport (substances move in opposite directions).

Examples:

Sodium-potassium pump (Na+/K+ pump): Moves three sodium ions out of the cell and two potassium ions into the cell against their respective concentration gradients, crucial for maintaining cell potential and volume.

Proton pump: Moves hydrogen ions (protons) across membranes, such as in the stomach lining cells to secrete gastric acid or in plant cells to maintain pH balance.

Function: Active transport is essential for maintaining cellular homeostasis, nutrient uptake, waste removal, and ion balance. It allows cells to absorb essential nutrients like glucose and amino acids, even when their concentrations are higher inside the cell than outside.

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