Types of Active Transport
There are two main types of active transport:
Primary Active Transport
Primary active transport, also called direct active transport, directly uses metabolic energy to move molecules across a membrane against their gradient. The most common example of this is the sodium-potassium pump (Na+/K+ pump), present in the cell membrane of most animal cells. The pump actively transports potassium ions into the cell and sodium ions out of the cell against their respective concentration gradients. This pump is crucial for maintaining the resting membrane potential and regulating the volume of individual cells. Different types of active transport are as follows:
- P-type ATPase: These are also referred to as E1-E2 ATPases because they have the ability to switch between two forms (E1 and E2). For example, they include the sodium-potassium pump (Na+/K+-ATPase), calcium pump (Ca2+-ATPase), proton-potassium pump (H+/K+ ATPase), and proton pump (H+ ATPase) found in plants and fungi.
- F-type ATPase: Alternatively known as ATP synthase or ATP phosphohydrolase (H+-transporter). Examples of this transport system include mitochondrial ATP synthase and chloroplast ATP synthase.
- V-type ATPase: These vacuolar proton-transporting ATPases are ATP-driven pumps located in the tonoplast of the cell. They harness the energy from ATP hydrolysis to transport protons across intracellular and plasma membranes of eukaryotic cells, resulting in many cell organelles having a more acidic environment than the surrounding cytoplasm. Mutational changes in this enzyme can lead to various consequences, such as cancer, neurodegenerative diseases, and aging. V-ATPases are complex multimeric proteins with two nearly separate domains, each with tissue-specific isoforms found in different organisms.
- ABC (ATP binding cassette) transporter: ABC transporters are a highly diverse class of carrier proteins that utilize energy derived from ATP hydrolysis to facilitate the movement of solutes across biological membranes
Secondary Active Transport
Secondary active transport, also known as cotransport, uses the energy created by primary active transport to transport other molecules against their concentration gradients. There are two subtypes of secondary active transport:
- Symport (cotransport): In symport, molecules move in the same direction as the ion that was pumped using primary active transport. For example, the sodium-glucose transporter (SGLT) is a symporter that uses the energy of the sodium gradient to move glucose into cells.
- Antiport (cotransport): In antiport, molecules move in the opposite direction of the ion pumped using primary active transport. An example is the sodium-calcium exchanger, which transports calcium out of the cell in exchange for sodium ions.
Active Transport
Active transport is a cellular process that uses energy mainly in the form of ATP, to move molecules or ions against their concentration gradients. It includes primary active transport, which directly uses energy for transport, and secondary active transport, which utilizes an electrochemical gradient to move other substances. It is essential for many physiological processes, including nutrient absorption in the digestive system, the transmission of nerve impulses, and the regulation of ion concentrations in cells.
Table of Content
- Active Transport Definition
- Types of Active Transport
- Examples of Active Transport
- Differences between Active Transport and Passive Transport