ACTIVE TRANSPORT

 ACTIVE TRANSPORT

• In Active processes, the cell must use energy (ATP) to move substances from areas of low concentration to areas of high concentration across the Plasma membrane.
• The substances Actively transported are Ions (Na⁺, K⁺, H⁺, Ca₂⁺ and CI^-), Amino acids and Simple sugars. Although these substances can also be moved into cells by passive processes, their movement by active processes can go against the concentration gradient, allowing a cell to accumulate needed materials.

(i) ATP - BINDING CASSETTE TRANSPORTERS (ABC transporters)

• ATP - binding cassette transporters (ABC transporters) are important examples of active transport systems. They are observed in Bacteria (most common in Gram negative bacteria), Archaea and Eukaryotes.

1)   The solute binding protein (Periplasmic binding protein) binds the substrate to be transported and approaches the ABC transporter complex.

2)  The solute binding protein attaches to the transporter and releases the substrate, which is moved across the membrane with the aid of ATP hydrolysis.

(ii) GROUP TRANSLOCATION

• In Active transport, the substance that crosses the membrane is not altered by transport across the membrane.
• In Group translocation, a special form of Active transport that occurs exclusively in Prokaryotes, the substance is chemically altered during transport across the membrane.
• Once the substance is altered and inside the cell, the plasma membrane is impermeable to it, so it remains inside the cell. This important mechanism enables a cell to accumulate various substances even though they may be in low concentrations outside the cell.
• Group translocation requires energy supplied by high -energy phosphate compounds, such as Phosphoenolpyruvic acid (PEP).
• One example of Group translocation is the transport of the sugars Glucose and Mannitol, which is often used in growth media for bacteria.