The key difference between cotransport and countertransport is that cotransport is a form of secondary active transport which transports two types of molecules simultaneously across the plasma membrane in the same direction or opposite direction. On the other hand, countertransport is one of the two forms of cotransport that transports two types of molecules simultaneously in opposite direction to each other across the cell membrane.
Molecules go in and out via the selective plasma membrane of the cell. There are several types of membrane transporting proteins. Cotransport and countertransport are two types of secondary active transport. Cotransport transports two different types of molecules at the same time in a coupled movement while countertransport or exchange is a type of cotransport that transports two types of molecules in the opposite direction across the membrane.
CONTENTS
1. Overview and Key Difference
2. What is Cotransport
3. What is Countertransport
4. Similarities Between Cotransport and Countertransport
5. Side by Side Comparison – Cotransport vs Countertransport in Tabular Form
6. Summary
What is Cotransport?
Cotransport or coupled transport is a type of secondary active transport that occurs in the cell membrane. It is energy-dependent, but it uses an electrochemical gradient instead of ATP to transport molecules. Cotransport transports two molecules simultaneously across the membrane. One molecule moves down an electrochemical gradient. The generating energy is then used to power the second molecule against its gradient. Likewise, two molecules travel together in the same direction or opposite direction at the same time. Depending on the direction of molecular movements, there are two types of cotransporters as symport and antiport. Symport transports both molecules in the same direction while antiport transports two molecules in opposite directions across a membrane.
Figure 01: Cotransport
Sodium is a cotransported ion. Hydrogen is another commonly cotransported ion. Sodium-glucose cotransport is another cotransport that works during intestinal glucose absorption. Na+/phosphate cotransporter, Na+/I− symporter, Na-K-2Cl symporter, GABA transporter and K+Cl− Symporter are several other examples of cotransporters.
What is Countertransport?
Countertransport or antiport or exchanger is a form of cotransporter present in the membrane. The key point regarding the countertransport is that it transports ions or molecules in opposite directions. So, one molecule comes out of the cell while the other one goes in at the same time across the membrane.
Moreover, this is a type of a secondary active transport that utilizes electrochemical gradient to power the movements. Countertransport may mediate the exchange of the same solutes or different solutes. Sodium-calcium exchanger, Na+/H+ exchanger and Cl–/bicarbonate exchanger are examples for countertransport.
What are the Similarities Between Cotransport and Countertransport?
- They are secondary active transporters located in the membrane.
- In fact, they are integral membrane proteins.
- Countertransport is a type of cotransport.
- Both transporters transport two types of molecules together at the same time.
- Both utilize electrochemical gradient to move ions across the membrane.
- There are two reactions: one is energetically favourable while the other one is energetically unfavourable.
- Furthermore, they undergo conformational changes during the transportation of ions.
What is the Difference Between Cotransport and Countertransport?
Cotransporter transports two molecules or ions simultaneously at the same time across the cell membrane while countertransporter is one of the two types of cotransporters which transports two molecules in opposite directions across the membrane. So, this is the key difference between cotransport and countertransport.
Below infographic gives more details on the difference between cotransport and countertransport.
Summary – Cotransport vs Countertransport
Cotransport or coupled transport is a secondary active transporter. It transports two molecules together at the same time across the cell membrane. Symport and antiport are two types of cotransport depending on the direction of molecules move. Antiport or countertransport is an exchanger which transports two molecules in opposite directions at the same time. Both cotransport and countertransport are integral membrane proteins that are found in many different cells and tissues and perform a variety of important physiological functions. So, this is the summary of the difference between cotransport and countertransport.
Reference:
1. “Secondary Active Transport.” PhysiologyWeb, Available here.
2. “Cotransporter.” Wikipedia, Wikimedia Foundation, 19 Feb. 2019, Available here.
Image Courtesy:
1. “Cotransporters” By Wikimedia user: Lupask – Wikimedia Commons (CC BY-SA 3.0) via Commons Wikimedia