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Facilitated diffusion is the movement of lipid insoluble molecules across the phospholipid bilayer by the use of carrier proteins[1]. Contents
Basic FeaturesThe bilayer consists of lipids, therefore only lipid-soluble molecules can pass through it. This is mainly small polar uncharged molecules and small hydrophobic molecules. Facilitated diffusion is a passive process that requires no use of external energy[1]. The action of facilitated diffusion is spontaneous, however, the rate of the diffusion differs according to how permeable a membrane is for each substance. Most membranes are selectively permeable so different membranes have different permeability. For example, water is diffused freely across cell membranes. Other substances, however, must pass through the lipid bilayer first.[2] The molecules move across the membrane from an area of high concentration to an area of low concentration. If the solute carries a net charge, for example, molecules will move down its electrochemical gradient[3].Sugars and amino acids are examples of molecules that move across the plasma membrane using facilitated diffusion. Also, GLUT transporters are a group of carrier proteins that move glucose sugars and associated hexose sugars across the plasma membrane[1]. Facilitated is characterised by the following:
Two major types of facilitated diffusion:1. Carrier proteinsThese are proteins that span the plasma membrane (transmembrane proteins) and are also known as permeases[4]. Each protein carrier is specific to bind to a complementary molecule. On one side of the membrane (higher concentration of molecules), the molecules bind to the carrier protein. The carrier then changes conformational shape, moving the binding site from one side of the membrane to the other[5], releasing the molecules on the other side of the membrane (where there is a lower concentration of the molecules)[6]. 2. Ion channel proteinsUnlike carrier proteins, ion channel proteins have gate to control the passage of substances across the cell membrane, down their electrochemical gradient, usually by the ligand-gated ion channel, voltage-gated ion channel or intracellular messenger-gated ion channel[7]. Ion channels are integral membrane proteins (hydrophobic region) that do not require binding of solutes but only allow specific types of solutes to pass through the protein channel[8]. There are three forms of transport can with facilitated diffusion ;
Factors affecting rate of facilitated diffusion
References
What is it called when molecules move across the cell membrane from an area of high concentration to an area of low concentration with the help of a carrier protein?An example of passive transport is diffusion, the movement of molecules from an area of high concentration to an area of low concentration. Carrier proteins and channel proteins are involved in facilitated diffusion.
What is it called when molecules move across the cell membrane from an area of high concentration?Diffusion. Diffusion is essentially the movement of molecules from a region of higher concentration to a region of lower concentration as a result of thermal motion. Diffusion is an important process in human physiology.
What is the movement across the cell membrane called?Active transport is the movement of molecules across a cell membrane in the direction against their concentration gradient, going from a low concentration to a high concentration.
What do you called the movement of molecules from the area of high concentration to the area of lower concentration?Diffusion: Diffusion is the movement of particles from an area of higher concentration to lower concentration.
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