Primary vs Secondary Active Transport Show
Active transport is a method that transports many substances across biological membranes, against their concentration gradients. In order to push molecules against a concentration gradient free energy is expended. In eukaryotic cells, this occurs at the plasma membrane of the cell and membranes of specialized organelles such as mitochondria, chloroplast etc. Active transport requires highly specific carrier proteins in the plasma membrane and these proteins have the ability to carry substances against a concentration gradient, hence referred to as ‘pumps’. Main roles of active transport include prevention of cell lysis, maintaining unequal concentrations of different ions on either side of the cell membrane, and maintaining electrochemical balance across the cell membrane. Active transport can occur in two different ways, namely, primary active transport and secondary active transport. What is Primary Active Transport? In primary active transport, positive charged ions (H+, Ca2+, Na+, and K+) are moved across membranes by transport proteins. The primary active transport pumps such as photon pump, calcium pump, and sodium-potassium pump are very important to maintain the cellular life. For example, calcium pump maintains the Ca2+ gradient across the membrane, and this gradient is important to regulate cellular activities such as secretion, microtubule assembly, and muscle contraction. Also, Na+/ K+ pump maintains the membrane potential across the plasma membrane. What is Secondary Active Transport? The energy source of secondary active transport pumps is the concentration gradient of an ion established by primary energy pumps. Therefore, the transferring substances are always coupled with transfer ions that are responsible for the driving force. In most animal cells, the driving force for secondary active transport is the concentration gradient of Na+/ K+. Secondary active transport occurs by two mechanisms called antiport (exchange diffusion) and symport (cotransport). In antiport, driving ions and transport molecules move in the opposite direction. Most of the ions are exchanged by this mechanism. For example, coupled movement of chloride and bicarbonate ions across the membrane is initiated by this mechanism. In symport, the solute and driving ions move towards the same direction. For example, sugars such as glucose and amino acids are transported across the cell membrane by this mechanism. What is the difference between Primary and Secondary Active Transport? • In primary active transport, the proteins hydrolyze ATP to power the transport directly whereas, in secondary active transport, ATP hydrolysis is done indirectly to power the transportation. • Unlike the proteins involved in primary active transport, transport proteins involved in secondary active transport do not break ATP molecules. • The driving force for the secondary active pumps is obtained from the ion pumps resulted from the primary active transport pumps. • Ions such as H+, Ca2+, Na+, and K+ are transported through the membrane by primary active pumps, whereas glucose, amino acids, and ions like bicarbonate, and chloride are transported by secondary active transport. • Unlike the secondary active transport, primary active transport maintains the electrochemical gradient across the plasma membrane. The active transport of molecules across cell membranes is one of the major factors on molecular level for keeping homeostasis within the body. This kind of transport requires energy as they transport molecules against their concentration gradient. It is divided into two types according to the source of energy used, called primary active transport and secondary active transport. In primary active transport, the energy is derived directly from the breakdown of ATP. In the secondary active transport, the energy is derived secondarily from energy that has been stored in the form of ionic concentration differences between the two sides of a membrane. Cell Membrane[edit | edit source]The cell membrane consists of a lipid bilayer including a large amount of protein molecules. These are considered as integral or peripheral membrane proteins. The lipid bilayer constitutes a barrier for the movement of different substances. However, some substances, especially lipid-soluble substances, are still able to pass this lipid bilayer through diffusion. The membrane proteins show different properties for the transport of substances. Their molecular structures interrupt the continuity of the lipid bilayer and thereby constitute an alternative pathway through the cell membrane. Hence the vast majority of the membrane proteins are regarded as transport proteins. They play a crucial role in keeping the ion concentration intracellular and extracellular on a physiological level. The way how transportation is achieved differs among three groups of transport proteins.
The substances that are transported across the membrane can cross alone, along with other molecules or in exchange:
Primary Active Transport[edit | edit source]Primary active transport utilizes energy in form of ATP to transport molecules across a membrane against their concentration gradient. Therefore, all groups of ATP-powered pumps contain one or more binding sites for ATP, which are always present on the cytosolic face of the membrane. Based on the transport mechanism as well as genetic and structural homology, there are considered four classes of ATP-dependent ion pumps:
The P-, F- and V-classes only transport ions, while the ABC superfamily also transports small molecules. The energy expended by cells to maintain the concentration gradients of some ions across the plasma and intracellular membranes is considerable:
Example: Na+/K+ pump Secondary Active Transport[edit | edit source]Secondary active transport, is transport of molecules across the cell membrane utilizing energy in other forms than ATP. This energy comes from the electrochemical gradient created by pumping ions out of the cell. This Co-Transport can be either via antiport or symport. Example : Na+ / glucose co-transporter The formation of the electrochemical gradient, which enables the co-transport, is made by the primary active transport of Na+. Na+ is actively transported out of the cell, creating a much higher concentration extracellularly than intracellularly. This gradient becomes energy as the excess Sodium is constantly trying to diffuse to the interior. This mechanism provides the energy needed for the co-transport of other ions and substances. This is evident in co-transporters such as the Sodium-glucose co-transporter. The Na+ gradient created by the Na+/K+ ATPase is used by the Na+/Glucose co-transporter to transport glucose and Na+ back into the cell. Links[edit | edit source]Related articles[edit | edit source]Bibliography[edit | edit source]
What are the difference between primary and secondary active transport?In primary active transport, the energy is derived directly from the breakdown of ATP. In the secondary active transport, the energy is derived secondarily from energy that has been stored in the form of ionic concentration differences between the two sides of a membrane.
What is the difference between the two types of active transport?Active transport pumps molecules or substances against a concentration gradient using cellular energy. In primary active transport, ATP is used in form of the energy. In secondary active transport, the electrochemical gradient is used to transport molecules across the membrane.
Which of the following is a difference between primary active transport and facilitated diffusion?Facilitated diffusion occurs along a concentration gradient from high concentration to low concentration and does not require energy, while active transport from low concentration to high concentration occurs against the concentration gradient and requires energy.
What are 2 similarities and 2 differences between passive and active transport?Active transport requires energy for the movement of molecules whereas passive transport does not require energy for the movement of molecules. In active transport, the molecules move against the concentration gradient whereas in passive transport, the molecules move along the concentration gradient.
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Which of the following is a difference between primary and secondary active transport
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