Main difference - active vs. passive transport
Active and passive transport are two methods that transport molecules across the cell membrane . A cell membrane is a multitasking unit that gives the cell structure and at the same time protects the cytosolic contents from the extracellular environment. The movement of molecules in and out of the cell is determined by the phospholipid bilayer, which maintains delicate homeostasis of the cell. The phospholipid bilayer is semi-permeable so that some molecules can pass the membrane unhindered by a concentration gradient and some molecules use special structures to cross the membrane and others to cross the membrane using cell energy. The main difference between active and passive transport is that active transport pumps molecules against the concentration gradient using ATP energy, while passive transport allows molecules to cross the membrane through a concentration gradient using no cell energy .
This article is about,
1. What is active transport - definition, types, function, mode of operation 2. What is passive transport - definition, types, function, mode of operation 3. What is the difference between active and passive transport?
What is active transportation?
Active transport is the movement of molecules across the membrane against the concentration gradient with the help of enzymes and the use of cellular energy. It is needed for the accumulation of molecules such as glucose , amino acids and ions in high concentrations in the cell. Two types of active transport can be distinguished: primary active transport and secondary active transport.
Primary active transport
In primary active transport, the presence of substances in the extracellular fluid required by the cell is recognized by the specialized transmembrane proteins on the cell membrane, which act as pumps for transport molecules. These transmembrane proteins are powered by ATP. The primary active transport is most evident in the sodium / potassium pump (Na + / K + ATPase), which maintains the resting potential of the cell. The energy released during the hydrolysis of ATP is used to pump 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 extracellular fluid. The proton / potassium pump (H + / K + ATPase) is located in the gastric mucosa and ensures an acidic environment in the stomach. Omeprazole is a proton / potassium pump inhibitor that reduces acid reflux in the stomach. During both oxidative phosphorylation and photophosphorylation of the electron transport chain, the primary active transport is used to also generate a reducing force. The effect of the sodium / potassium pump is shown in Figure 1 .
Figure 1: Sodium / Potassium Pump
Secondary active transport
The secondary active transport is driven by an electrochemical gradient. Here channels are formed by pore-forming proteins. During secondary active transport, simultaneous movement of another substance against the concentration gradient is observed. Therefore, the channel proteins involved in secondary active transport can be identified as cotransporters. There are two types of cotransporters: antiporters and symporters. A particular ion and the solute are transported in opposite directions by antiporters. The most common example of antiporters is the sodium / calcium exchanger, which enables the calcium ion concentration in the cardiomyocyte to be restored to the action potential. Ions are transported through the concentration gradient, while the solute is transported against the concentration gradient by symporters. Both molecules are transported across the cell membrane in the same direction. SGLT2 is a symporter that transports glucose into the cell together with the sodium ions. The function of the symporter and antiporter is shown in Figure 2 .
Figure 2: The effect of Symporter and Antiporter
What is passive transport?
Passive transport is the movement of molecules across the membrane through a concentration gradient without using cell energy through movement. It uses natural entropy to move molecules from a higher concentration to a lower concentration until the concentration is balanced. Then there is no net movement of the molecules in equilibrium. Four main types of passive transport are found: osmosis , simple diffusion, facilitated diffusion, and filtration. The simple movement of molecules through a permeable membrane is called simple diffusion . Small, non-polar molecules use simple diffusion. The diffusion distance should be less to maintain better flow. The passive transport through the membrane is shown in Figure 3 .
Figure 3: Passive transport
In facilitated diffusion , special transport proteins are used to direct the movement of polar molecules and large ions. These transport proteins are glycoproteins and are specific for a particular protein. The GLUT4 is a glucose transporter that transports glucose from the bloodstream into the cell. It is found primarily in fat and skeletal muscles. Three types of transport proteins are involved in facilitating diffusion: channel proteins, aquaporins and carrier proteins. Channel proteins form hydrophobic tunnels through the membrane, which allows the selected hydrophobic molecules to pass through the membrane. Some channel proteins are open all the time, others are controlled like ion channel proteins . Aquaporins allow water to quickly pass through the membrane. Carrier proteins change their shape and transport target molecules through the membrane. The facilitated diffusion by carrier proteins is shown in Figure 4.
Figure 4: Facilitated diffusion
Filtration is the movement of solutes along with water due to the hydrostatic pressure created by the cardiovascular system. It is found in Bowman's capsule in the kidney. Osmosis is the movement of water through a selectively permeable membrane. It occurs from a high water potential to a low water potential.
Difference between active and passive transport
definition
Active transport: Active transport pumps molecules against the concentration gradient across the cell membrane.
Passive transport: Passive transport enables molecules to cross the cell membrane through a concentration gradient.
Cellular energy consumption
Active transport: Active transport uses cellular energy in the form of ATP.
Passive transport: Passive transport does not require cellular energy.
Modes of transport
Active transport: endocytosis, exocytosis , secretion of substances into the bloodstream and sodium / potassium pump are the types of active transport.
Passive transport: Diffusion, facilitated diffusion and osmosis are the types of passive transport.
role
Active transport: Active transport allows molecules to cross the cell membrane, disrupting the equilibrium created by diffusion.
Passive transport: A dynamic balance of water, nutrients, gases and waste is maintained through passive transport between the cytosol and the extracellular environment.
Transporting particles
Active transport: Ions, large proteins, complex sugars and cells are transported by active transport.
Passive transport: Water-soluble molecules such as small monosaccharides, lipids, sex hormones, carbon dioxide, oxygen and water are transported through passive transport.
meaning
Active transport: Active transport is required for large, insoluble molecules to enter the cell.
Passive transport: Passive transport enables the maintenance of a sensitive homeostasis between the cytosol and extracellular fluid.
diploma
Active and passive transport are the two methods used to move molecules across the cell membrane. Active transport pumps molecules against a concentration gradient using cellular energy. In primary active transport, ATP is used as energy. In secondary active transport, the electrochemical gradient is used to move molecules across the membrane. Active transport concentrates nutrients in the cell. Passive diffusion allows small, non-polar molecules to move through the membrane. It only occurs through a concentration gradient. Therefore, no energy is consumed by the process. Osmosis and filtration are also passive diffusion methods. However, the main difference between active transport and passive transport lies in their mechanisms of transporting molecules across the membrane.
Reference: 1. "Passive transport and active transport across a cell membrane article (article)." Khan Academy. Np, nd web. May 03, 2017. 2. “Diffusion and Passive Transport.” Khan Academy. Np, nd web. May 03, 2017.
Image courtesy: 1. "Sodium-Potassium-Pump-de" By LadyofHats Mariana Ruiz Villarreal - Own work. Image renamed from Image: Sodium-Potassium_pump.svg (Public Domain) via Commons Wikimedia 2. "Porters" By Lupask - Own work, Public Domain) via Commons Wikimedia 3. "Figure 05 02 02" By CNX OpenStax - (CC BY 4.0 ) via Commons Wikimedia 4. “Blausen 0213 CellularDiffusion” By Blausen.com employees (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
