The main difference between active transport and group translocation is that the active transport releases the exact molecules that have been taken up from the medium. But, in contrast, the molecules that have been taken up from the medium undergo modifications during the transport process. Furthermore, active transport uses chemical energy from ATP or electrochemical gradient for transport, while group translocation uses energy from organic compounds for the transport of molecules.
Active transport and group translocation are two types of membrane transport mechanisms by which different molecules in the medium are taken up into the cytoplasm through the cell membrane. Generally, group translocation is a type of active transport.
Key Areas Covered
1. What is Active Transport
– Definition, Mechanism, Importance
2. What is Group Translocation
– Definition, Mechanism, Importance
3. What are the Similarities Between Active Transport and Group Translocation
– Outline of Common Features
4. What is the Difference Between Active Transport and Group Translocation
– Comparison of Key Differences
Key Terms
Active Transport, ATP, Group Translocation, Primary Active Transport, PTS System, Secondary Active Transport
What is Active Transport
Active transport is the mechanism of transporting molecules across the plasma membrane against the concentration gradient by using energy. Generally, transmembrane carrier proteins take part in active transport. Also, two types of active transport mechanisms can occur in a cell; they are the primary active transport and secondary active transport.
Primary Active Transport
Primary active transport uses metabolic energy in the form of ATP to transport molecules across the membrane. Therefore, carrier proteins, which transport molecules by primary active transport, are always coupled with ATPase. The most common example of primary active transport is the sodium-potassium pump, which moves three Na+ ions into the cell while moving two K+ ions out of the cell. Thus, the sodium-potassium pump helps in maintaining the cell potential.
Figure 1: Sodium-Potassium Pump
Secondary Active Transport
On the other hand, secondary active transport relies on the electrochemical gradient of the ions on either side of the plasma membrane to transport molecules. That means; it uses the energy released by transporting one type of molecules through its concentration gradient to transport another type of molecule against the concentration gradient. Hence, transmembrane proteins involved in secondary active transport are cotransporters. Basically, the two types of cotransporters are symporters and antiporters. Of these, symporters transport both molecules in the same direction. Also, sodium-glucose cotransporter is a type of symporter. In the meanwhile, antiporters transport the two types of molecules to opposite directions. Here, the sodium-calcium exchanger is an example of an antiporter.
Figure 2: Porters
Apart from that, ABC (ATP-binding cassette) system in Gram-negative bacteria uses substrate-specific binding proteins in the bacterial periplasm to transport molecules.
What is Group Translocation
Group translocation is a unique type of active transport, using energy from the energy-rich organic compounds other than ATP. However, it differs from other cotransporters and the ABC system as molecules transported by group translocation undergo chemical modifications. In general, one of the commonest examples of such group translocation is the phosphotransferase (PTS) system in bacteria. Here, it is responsible for the sugar uptake while using energy from phosphoenolpyruvate (PEP), which is an energy-rich molecule. Usually, it is a multi-component system, which uses enzymes of the plasma membrane.
Figure 3: PTS System in Bacteria
Furthermore, after the translocation through the cell membrane, the transported molecules undergo modifications in the group translocation. Normally in the PTS system, a phosphate group is transferred from PEP to the transporting sugar. Besides, some of the sugars, which undergo translocation include glucose, fructose, mannose, and cellobiose.
Similarities Between Active Transport and Group Translocation
- Active transport and group translocation are two processes of membrane transport mechanisms.
- They are responsible for the transport of molecules from the medium through the cell membrane into the cytoplasm.
- Also, they transport molecules against a concentration gradient by using cellular energy with the help of transporter proteins.
- Both mechanisms are important for uptaking nutrients and other ions into the cell.
Difference Between Active Transport and Group Translocation
Definition
Active transport refers to the movement of ions or molecules across a cell membrane into a region of a higher concentration, assisted by enzymes and requiring energy. On the other hand, group translocation refers to a mechanism widely used for the transportation of sugars across bacterial membranes and perhaps those of some higher cells.
Types of Transporter Proteins
The four types of transport proteins of active transport are antiporters, symporters, ATP-binding cassette system, and group translocation. Meanwhile, the enzymes of the plasma membrane such as phosphotransferase (PTS) system take part in the group translocation.
Type of Energy
Active transport uses energy from ATP or electrochemical gradient, while group translocation uses the breakdown of high energy compounds such as PEP.
Types of Molecules Transported
Active transport moves glucose, amino acids, and ions into the cytoplasm, while group translocation transports many sugars such as glucose, mannose, fructose, and cellobiose into bacteria.
Modifications
Active transport releases exactly the same molecules that have been taken up from the medium, while molecules, which are taken up from the medium, undergo modifications during the transport process.
Conclusion
Active transport is a type of membrane transport mechanism, moving ions, glucose, and amino acids into the cell through the cell membrane. It uses either ATP in the primary active transport or an electrochemical gradient in secondary active transport. On the other hand, group translocation is a type of active transport, which uses the energy from PEP to transport sugars mainly in bacteria. However, both active transport and group translocation move molecules into the cytoplasm against a concentration gradient. Therefore, the main difference between active transport and group translocation is the type of energy, mechanisms, and molecules transported.
References:
1. “Transport Across the Cell Membrane|Boundless Microbiology.” Lumen, Available Here.
Image Courtesy:
1. “Scheme sodium-potassium pump-en” By LadyofHats Mariana Ruiz Villarreal – Own work. (Public Domain) via Commons Wikimedia
2. “Porters” By Lupask – Own work (Public Domain) via Commons Wikimedia
3. “Phosphotransferase system” By Yikrazuul – Own work; ISBN 978-3-13-444608-1; S. 505 (CC BY-SA 3.0) via Commons Wikimedia
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