Tag: Facilitated Diffusion
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Facilitated Diffusion: Definition, Physiology, and Examples
Continue ReadingFacilitated Diffusion: Definition, Physiology, and Examples
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Facilitated Diffusion: Definition, Types, and Examples
Continue ReadingFacilitated Diffusion Definition
Facilitated diffusion (also known as facilitated transport or passive-mediated transport) is the process of spontaneous passive transport (as opposed to active transport) of molecules or ions across a biological membrane via specific transmembrane integral proteins.
What is Facilitated Diffusion?
Facilitated Diffusion is a passive transport where the movement of molecules is mediated through the plasma membrane with the help of transporter protein such as carrier is called as facilitated diffusion.
The transfer of molecules takes place from a higher concentration area to a lower concentration in facilitated diffusion as well, like simple diffusion. The solute concentration variation through the membrane is the driving force responsible for facilitated diffusion.
Although majority of facilitated diffusion does not suffice the need of ATP, however in few cases it does require ATP. Facilitated diffusion take place due to the exactitude between the carriers and the solute.
In facilitated diffusion molecules can progress in both the direction i.e., towards or against the concentration gradient. Kinetic energy along with concentration gradient helps to carry out facilitated diffusion.
The molecules which can pass through are water soluble huge molecules through the plasma membrane in facilitated diffusion.
Facilitated Diffusion Principle
Plasma membrane’s lipid bilayer is hydrophobic, thus water-soluble molecules cannot pass through; however tiny water molecules due to their concentration gradient can pass through the membrane. Although hydrophobic huge molecule requires either carriers or channel protein to pass through the membrane.Â
When molecules passes with the help of the channel protein, there are pores present in the transmembrane of the membrane, resulting in the flow of molecules and are spread throughout the cytosol and outer surrounding thus, extending to the other organelles.
Through the transmembrane channel, charged molecules will move and these transporters protein are incorporated to the membrane, having attraction towards the matrix.
However, in other cases, molecule will attach to the carrier protein, which will change the shape of the molecule leading to the molecule move inside the cytosol, and this process is seen in enzymes, which are huge molecules.
Facilitated Diffusion and Channel Proteins
These proteins aid in the movement of molecules, by channel formation through the membrane and in this membrane lies the transmembrane proteins which are ions.
These channels have a diameter of 4-5 Armstrong and can be choosy and allow only a particular ion to move through such as positive ion and will have differences for various ions, thus being picky towards a particular ion. In the extra and intracellular matrix, hydrophilic domains and core are possessed by these channel, thus cracking the layers wide open.
The water movement through the membrane is mediated by the aquaporins at a very faster pace. On the receival of the electrical signal or attachment of molecule, the doors gets closed and open.
Facilitated Diffusion and Carrier Proteins
Carrier proteins perform facilitated diffusion, by transporting the molecules through the membrane. They do so by attaching to the molecule and getting changes in its shape as they are heavy and then it can move within the cell on the basis of the concentration.
The change in shape also has an impact on the hydrogen bonds. Carrier protein are quite specific in terms of their binding sites, such as they recognize between the D and L sugar type, which makes the plasma membrane as well specific.
Saturation occurs when carrier protein attaches to the substrate, thus allowing movement to take place at a faster pace. They play role in active transport which requires energy for the transportation of molecule.
Factors Affecting Facilitated Diffusion
Environmental factors are the one which has an impact on facilitated diffusion:
a) Concentration Gradient: The diffusion through the membrane occurs due to concentration gradient, which happens from a high concentrated region to a lower concentrated one. However quick diffusion happens due to the concentration diffusion.
b) Temperature: For the shape to change, the amount of energy required is quite high than the activation energy. As the temperature increases the carrier transportation also increases, thus elevating the reaction rate between the carrier protein and the substrate in the molecule.
c) Saturation: On the membrane, carrier proteins are present in specific amount and once these sites are occupied, no more proteins can bind. Thus, even if concentration gradient rate is elevated, rate of diffusion cannot be elevated.
d) Selectivity: Selectivity and transportation rate are reciprocal to each other, as selectivity is achieved from the binding sites which do not treat all the solutes equally, thus ceasing the movement.
Facilitated Diffusion Examples
1) Glucose and amino acid transport: Example is the movement of glucose and amino acid from blood to the cell is the facilitated diffusion example. Through active transport they reach the intestine and are left into the blood. These molecules are moved to cell from the blood through carriers such as amino acid permease and glucose transporters, as they are quite huge.
2) Gas transport: A different example is when to the muscle and the blood, oxygen is transported. The carrier protein is hemoglobin blood and myoglobin in muscle, which results in diffusion due to increase in pressure and thus gets moved to the other side with low pressure. The same process is involved in carbon monoxide and dioxide.
3) Ion transport: Ions possess the same charge like the membrane and are polar thus, cannot move through and thus have transmembrane protein also known as ion channel which are choosy for ions like Na, K and Ca and the transport has to be quick as no energy is used.
Biological Importance of Facilitated Diffusion
The homeostasis between the outer and inner environment is regulated by facilitated diffusion. It also makes the biological membranes specific. Various functions are regulated by facilitated diffusion such as ion transport, oxygen transport and transportation of sugar molecules.
Facilitated Diffusion Citations
- Facilitated diffusion in chromatin lattices: mechanistic diversity and regulatory potential. Mol Microbiol . 2005 Aug;57(4):889-99.
- Facilitated Diffusion Mechanisms in DNA Base Excision Repair and Transcriptional Activation. Chem Rev . 2018 Dec 12;118(23):11298-11323.
- Facilitated diffusion of Argonaute-mediated target search. RNA Biol . 2019 Sep;16(9):1093-1107.
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Facilitated Diffusion: Definition, Mechanism, and Examples
Continue ReadingFacilitated Diffusion Definition
The transport of substances from their higher concentration to lower concentration with the help of any transport molecule is known as facilitated diffusion. In facilitated diffusion, the substances move across a biological membrane along the direction of their concentration gradient. It doesn’t require chemical energy.
There are some common examples of living processes that require facilitated diffusion for their completion. These biological processes include amino acid and glucose transport, gas transport, and ion transport.
Facilitated diffusion has great significance because it balances the transport of molecules from the plasma membrane. The plasma membrane or cell membrane is an outermost covering of cells that is selectively permeable hence it only allows selective molecules to transport through the membrane.
It can be defined as following- “The passive movement of substances, across the plasma membrane by the help of some transport proteins found in the cell membrane.”
Facilitated Diffusion Etymology
The term facilitated diffusion is consisting of two words where facilitated came from the Latin word facilis, meaning “make” and the word diffusion meaning “a pouring fort”. Facilitated diffusion is also known as passive-mediated transport.
Characteristic Features of Facilitated Diffusion
Cellular transport is of two types- Active transport and passive transport. Facilitated diffusion is a type of passive transport where substances move from their higher concentration to lower concentration. This concentration difference creates a gradient that encourages substances to constitutionally move and to distribute between two areas to achieve equilibrium.
Facilitated diffusion does not require chemical energy because it directs movement from higher to lower concentrations. So, the process completes with the kinetic energy of the cell. The process differs from other types of passive transport due to the assistance of transport proteins while other passive transport does not require any transport protein.
Facilitated Diffusion Diagram
Facilitated Diffusion Mechanism
The plasma membrane is composed of a lipid bilayer which regulates the passage of molecules across the membrane. The hydrophobic region of the membrane is located outwards and thus it prevents polar (hydrophilic) molecules to cross the membrane directly. However, the non-polar or hydrophobic molecules can easily diffuse through the membrane along with their concentration gradient.
Thus large polar molecules take on certain membrane proteins like channels and carriers to diffuse through the plasma membrane.
Now facilitated diffusion can be categorized into different types based on membrane proteins engaged.
E.g.- Facilitated diffusion by channel proteins- It is a type of diffusion that uses certain membrane proteins that act as a pore in the lipid bilayer. The most common example of channel proteins is transmembrane channels which form by protein complexes that span across the plasma membrane.
These channels help several charged ions to be transported across the plasma membrane. Besides channels, there are some other proteins like aquaporins, which are also integral membrane proteins involves in the transport of water molecules.
Another example of proteins involved in facilitated diffusion is carrier proteins. Carrier proteins can transport the larger molecules by changing their conformation during the transportation of molecules across the membrane (e.g. permeases).
Facilitated Diffusion Examples
i. Glucose and Amino Acid Transport
Glucose is a large polar molecule that is transported by the process of facilitated diffusion. Glucose transporters are types of carrier proteins that mediate the transport of glucose across the lipid bilayer. The glucose taken in the diet is absorbed by the small intestine by active transport.
In the bloodstream it is released via facilitated diffusion and other body organs, cells also take glucose vias facilitated diffusion. Similarly, amino acids are also a type of biomolecules that moves from the bloodstream into the cell by facilitated diffusion.
ii. Ion Transport
The charged ions cannot diffuse through the plasma membrane directly due to the charge of those ions. Thus, these ions are also to be transported by facilitated diffusion. Some common examples of proteins are sodium ions, calcium ions, potassium ions.
Facilitated Diffusion vs Active Transport
Active transport is a type of transport that also needs a concentration gradient to complete the process. Ions, sugars, and salts can be transported by any of the transportation methods. Both the methods use transport vehicles for transport. However, there are some differences between facilitated diffusion and active transport. The major difference is the direction of transport.
Facilitated diffusion transports the substances from their higher concentration to lower concentration whereas Active transport facilitates the flow of substances from lower to higher concentration. This against the concentration gradient movement of substances requires chemical energy in the form of ATP. facilitated diffusion does not require chemical energy.
Simple Diffusion vs Facilitated Diffusion
Both are the type of passive transport where substances move along with their concentration gradient. The processes differ in the way of transporting molecules across the membrane. There are some transport proteins required in the process of facilitated diffusion to transport substances whereas simple diffusion, does not require any transport proteins. The rate of the process also differs which tends to be affected by saturation limits in facilitated diffusion and the rate is more straightforward in simple diffusion.
Importance of Facilitated Diffusion
There is an unequal distribution of molecules between the intracellular region and extracellular region that enhances cellular transport. To establish equilibrium between these two regions, the movement of substances is very crucial. Facilitated diffusion plays an important role to transport certain polar and charged molecules that cannot transport via simple diffusion. It is also helpful in maintaining homeostatic optimal levels of molecules.
Facilitated Diffusion Citations
- Pyogenic cerebral abscesses demonstrating facilitated diffusion. Clin Neurol Neurosurg . 2016 May;144:77-81.
- Aquaporin-facilitated transmembrane diffusion of hydrogen peroxide. Biochim Biophys Acta . 2014 May;1840(5):1596-604.
- Effect of DNA conformation on facilitated diffusion. Biochem Soc Trans . 2013 Apr;41(2):582-8.
- Facilitated diffusion of glucose. Physiol Rev . 1990 Oct;70(4):1135-76.
- Facilitated diffusion in chromatin lattices: mechanistic diversity and regulatory potential. Mol Microbiol . 2005 Aug;57(4):889-99.
- Facilitated Diffusion Mechanisms in DNA Base Excision Repair and Transcriptional Activation. Chem Rev . 2018 Dec 12;118(23):11298-11323.Â
- Facilitated diffusion of Argonaute-mediated target search. RNA Biol . 2019 Sep;16(9):1093-1107.
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Facilitated Diffusion: Definition, Mechanism, and Examples
Continue ReadingWhat is Facilitated Diffusion?
Active and passive transport are the 2 main transport mechanisms mediating commination between an environment and a plant in which organizing tissues are directly interconnected and respond to environmental changes directly. Lack of central organizing unit and control mechanism in lower organisms such as plants directly interact with the environment at cellular or tissue level massively depends on Active and Passive transports. In plants water is a main element of circulation and in assimilation of CO2 to sucrose; absorbed in root hairs Passive uptake of water – Diffusion and facilitated diffusion.
Facilitated diffusion – a modified mechanism of diffusion; involves membrane transporters to allow water and other molecules on difference between concentration and electrochemical gradient. In 1930, passive transport of water in cells were experimented by artificially creating a cell to understand the better transport mechanism; resulted in efficient flow of water and minerals through membrane transporters in facilitated diffusion rather than through lipid bilayers as in simple diffusion. Facilitated diffusion is bi – directional depending upon either concentration gradient and electrochemical gradient. At equilibrium, the rate of transport of net molecules of water or other elements is minimal or null.
Schematic Representation of Facilitated Diffusion
Facilitated Diffusion Characteristic
1. Specificity: Transmembrane proteins are frequent in between sets of lipid bilayer. Molecules of transport are permitted in specific transporter molecules depending upon the molecule that enters a cell.
2. Passive Nature: Transport through the channels does not require the conversion of ATP into ADP or AMP to power the movement of molecules from higher concentration to lower concentration.
3. Saturation Kinetics: Apart from the specificity and passive transport; driving force of the net movement of molecules depends on the concentration or the net number of molecules present between external and internal environment of cell.
Facilitated Diffusion Citations
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