Key difference - primary vs. secondary active transport

Active transport is the movement of molecules through the cell membrane against the concentration gradient with the help of enzymes and the use of cell energy. Active transport is divided into two types, known as primary and secondary active transport, depending on the energy source used to transport molecules. The main difference between primary and secondary active transport is that molecules are transported through the breakdown of ATP in primary active transport, while in secondary active transport the concentration gradient of one molecule provides the energy for the transport of another molecule against its concentration gradient.

Key areas covered

1. What is primary active transport - definition, types, properties 2. What is secondary active transport - definition, types, properties 3. What are the similarities between primary and secondary active transport - overview of the common characteristics 4. What is the difference Between Primary and Secondary Active Transport - Comparison of Key Differences

Key terms: antiport, ATP, concentration gradient, electrochemical gradient, ion-coupled transport, primary active transport, secondary active transport, symport, transmembrane proteins

What is primary active transport?

Primary active transport is the transport of molecules against a concentration gradient using energy from ATP. Transmembrane proteins are involved in controlling the passage of molecules across the cell membrane. They contain one or more ATP binding sites on their cytosolic side. In primary active transport, the energy is transferred to the transmembrane protein and then to the concentration gradient. The primary active transport is most evident in the sodium / potassium (Na ⁺ / K ⁺ ATPase) pump, which maintains the resting potential of the cells. The hydrolysis of an ATP pumps three sodium ions out of the cell and two potassium ions into the cell. Sodium ions are transported from a lower concentration of 10 mM to a higher concentration of 145 mM. Potassium ions are transported from a concentration of 140 mM within the cell to a concentration of 5 mM in the extracellular fluid. The proton / potassium pump (H + / K + ATPase) is located in the gastric mucosa and ensures an acidic environment in the stomach.

Figure 1: Sodium-Potassium Pump

What is secondary active transport?

Secondary active transport is the other type of active transport that uses the electrochemical gradient in transporting molecules against the concentration gradient. Transmembrane proteins involved in secondary active transport are identified as cotransporters because they transport two types of molecules at the same time. For this reason, the secondary active transport is called ion-coupled transport . Typically, one ion (driving ion) is transported through its electrochemical gradient while another ion or solute (driven ion / molecule) is transported against the electrochemical gradient. The concentration gradient of the driving ion provides the energy for the transport of the driven ion / molecule against its concentration gradient. The maintenance of the concentration gradient of the driving ion is achieved through primary active transport.

Symport and antiport are the two types of secondary active transport. In Symport , both driving and driven molecules are transported in the same direction. The Na ⁺ / glucose cotransporter (SGLT1) is an example of symport in which both sodium and glucose are transported into the cell. It occurs in the proximal tubules of the kidney and in the small intestine. With the antiport , driving and driven ions are transported in opposite directions. The Na ⁺ / Ca ²⁺ exchanger (NCX) in muscle cells transports sodium ions into the cell, while calcium ions are transported out of the cell. The sodium / glucose pump is shown in Figure 2 .

Figure 2: Sodium / glucose pump

Similarities Between Primary and Secondary Active Transport

• Both primary active transport and secondary active transport are two active transport methods.

• Both methods are involved in pumping molecules against the concentration gradient from a low concentration to a high concentration.

• Transmembrane proteins are involved in facilitating primary and secondary active transport.

• Transmembrane proteins are specific for the molecules transported across the membrane.

• The main purpose of both transport methods is to accelerate the movement of molecules across the cell membrane.

Difference between primary and secondary active transport

definition

Primary Active Transport: Primary active transport is the transport of molecules against a concentration gradient using energy from ATP.

Secondary active transport: Secondary active transport is the transport of two different molecules across a transport membrane using energy in forms other than ATP.

Coupled transport

Primary active transport: A single molecule is transported in primary active transport.

Secondary active transport: In secondary active transport, two types of molecules are transported at the same time.

Energy source

Primary Active Transport: Primary active transport uses energy from ATP.

Secondary active transport: The concentration gradient of the driving ion provides the energy for the transport of the driven ion / molecule against its concentration gradient during secondary active transport.

Types of molecules

Primary active transport: Ions such as sodium, potassium and calcium are transported through the cell membrane during primary active transport.

Secondary active transport: Ions serve as driving molecules, while ions or other molecules serve as driven molecules.

Types

Primary active transport: transmembrane proteins are unique to the ion they transport.

Secondary active transport: Symports and antiports are the two types of transmembrane proteins involved in secondary active transport.

Examples

Primary active transport: Sodium-potassium pump, calcium pump in the muscles, and proton pump in the stomach are examples of primary active transport.

Secondary active transport: glucose-sodium pump, Na ⁺ / Ca ²⁺ exchanger and sodium / phosphate cotransporter are examples of secondary active transport.

diploma

Primary and secondary active transport are the two variants of active transport of molecules across biological membranes. The main difference between primary and secondary active transport is the energy source used by each method of transport to move molecules across the cell membrane. The primary active transport uses the energy of ATP to move a single molecule across the cell membrane at a time. Secondary active transport transports two molecules across the membrane at the same time; the concentration gradient of the driving ion provides energy for the transport of the driven molecule during secondary active transport.

Reference:

1. "Active Transport". Khan Academy. Np, nd web. Available here . June 15, 2017. 2. “Primary active traffic”. Limitless. Np, May 26, 2016. Web. Available here . June 15, 2017.3. "Secondary Active Transport." PhysiologyWeb. Np, nd web. Available here . 15th June 2017.

Image courtesy:

1. "Blausen 0818 sodium-potassium pump" employee of Blausen.com (2014). "Medical Gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI: 10.15347 / wjm / 2014.010. ISSN 2002-4436. - Own work (CC BY 3.0) via Commons Wikimedia 2. "Figure 05 03 04" By CNX OpenStax - (CC BY 4.0) via Commons Wikimedia