Facilitated Diffusion | Definition , Factors and Example

By | October 23, 2019

Facilitated Diffusion

Facilitated Diffusion Definition:

What is Facilitated Diffusion: It is a type of facilitated transport that involves the passive movement of molecules along their concentration gradient, which is guided by the presence of another molecule. Facilitated diffusion is not involving high energy molecules directly, such as ATP (adenosine triphosphate) or GTP (guanosine triphosphate) since the molecules move along their concentration gradient.

Facilitated diffusion is the transport of substances across the membrane from a higher concentration area to the lower concentration area by the carrier molecules. It does since the substances move to the direction of their concentration gradient.

Facilitated Diffusion

Factors Affecting Facilitated Diffusion:

The force which is driving behind the diffusion of fluids is the probability behind Brownian motion simply. All the molecules are having some degree of random movement, erratic, and largely dependence on temperature. The energy of the molecules increases as the temperature increases.

When a substance becomes highly concentrated in certain regions, the molecular movement will lead to the gradual spreading of the substance. When all of the molecules are moving randomly within a region, then the some bound to move outward into the region of low concentration. Sometimes, it refers that the random movement of molecules will result in the directional movement from the low concentration region towards the high concentration region. The diffusion does not depend on the concentration of any other substance present in the medium.

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Facilitated Diffusion Across Membranes:

Does facilitated diffusion require energy: Diffusion is the ubiquitous across to the biosphere as it lies in the movement of water and air, and it is necessary driving force global weather patterns. The presence of lipid-based membranes within a living system produces compartments that permit the selective concentration of water-soluble substances.

The ions, proteins, small molecules, and other solutes are having different concentrations across the lipid bilayers. Although, charged or hydrophilic molecules cannot be traverse biological membranes. On the other hand, it is useful in order to maintain the integrity of each compartment, it is also important for molecules to move across the membrane along to their concentration gradient.

Diffusion of Gases:

A good example of the diffusion of gases is the movement of carbon dioxide and oxygen in actively respiring tissues and cells. These cells require the input of oxygen and glucose, and carbon dioxide requires to be removing from the body and expelled from the body. So, each molecule moves from the high concentration region toward the low concentration region. And there is no direct involving of ATP or other molecules. They have to cross multiple lipid bilayers from the mitochondrial membrane to the plasma membrane.

Need for Facilitated Diffusion:

The cell membranes are freely permeable to a very limited class of molecules. They have must be small size and non-polar. It permits molecules, such as oxygen, carbon dioxide, and water, to diffuse across the membrane. It precludes every biopolymer practically, most of the nutrients and many small molecules. The transmembrane proteins have two kinds of transferring; one form which acts like carrier and another form channel across the membrane.

Carrier and Channels:

Integral membrane proteins are made up of long hydrophobic stretches interspersed with the hydrophilic areas, so the study of these is difficult.

The carrier proteins are involved in the facilitated diffusion having two conformations. The binding of the molecule on one side of the membrane induces a change in the three-dimensional structure of the protein that permits the passage of molecule by the other side.

The proteins which form channels have minute pores that allow specific molecules to pass through selectively. Many mechanisms used to determine the fit between a molecule and its channel proteins as from the size, to charge and the ability to interact with amino acid side chains lining the pore. Some proteins channel may express a thousandfold preferences for one molecule over the other biochemically similar substances.

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Examples of Facilitated Diffusion:

Many molecules undergo facilitated diffusion to move between the cells and the subcellular organelles. Some examples are given below:

  • Glucose Transporter:

When the process of food digestion takes place, the small intestine has a high concentration of glucose. The glucose transports throughout the body by the circulatory system. When blood flow through tissues requires energy, the glucose again traverses the endothelial cell membrane and enters cells with a low concentration of glucose.

The glucose transporter carries protein which has two major conformational structures. The three-dimensional structure not knowing the binding of glucose probably causes the conformational change which makes the binding site face the interior of the cell. When glucose releases into cell, the transporter returns back to its original conformational.

  • Ion Channels:

Ion channels proteins form pores on the lipid bilayer which can be open or closed confirmation depends on the electrical potential of the cell and binding of ligands. These proteins are known as “gated” channels, in this scene.

In most cells, ion pumps present to ensure that the ionic composition of the extracellular fluids is different from the cytosol.

The binding of neurotransmitters, such as acetylcholine, to the receptors on muscle cells, have to change the permeability of the ligand-gated ion channel. The transmembrane channel is made by multiple subunits which are arranged as closed cylinders. The binding of ligand changes the conformation of hydrophobic side chains which block the central passage. This is a cause of the rapid influx of sodium ions into muscles. The change in electric potential of cell results in the opening of the calcium ion channel, which lead to the contraction of muscle fiber.

  • Aquaporins:

Like other transmembrane proteins, aquaporins are not characterized completely. There are many such channels for rapid passage of molecules of water in each cell. These proteins with high concentrations present in bacteria, plants, fungi, and animals. The mutation is proteins from aquaporins which can lead to diseases such as diabetes insipidus.