can you please explain the meaning of micelles found When breaking down of fats occurs... with proper diagram?????
Answers
Most of the fat in the human diet is in the form of triacylglycerol (TAG), which consists of three fatty acids linked to glycerol. In the digestive tract, TAG is hydrolyzed by the enzyme pancreatic lipase, to release free fatty acids and monoglycerides.
Emulsification and digestion
The key issue in the digestion and absorption of fats is one of solubility: lipids are hydrophobic, and thus are poorly soluble in the aqueous environment of the digestive tract. The digestive enzyme, pancreatic lipase, is water soluble and can only work at the surface of fat globules. Digestion is greatly aided by emulsification, the breaking up of fat globules into much smaller emulsion droplets. Bile salts and phospholipids are amphipathic molecules that are present in the bile. Motility in the small intestine breaks fat globules apart into small droplets that are coated with bile salts and phospholipids, preventing the emulsion droplets from re-associating.
The emulsion droplets are where digestion occurs. Emulsification greatly increases the surface area where water-soluble pancreatic lipase can work to digest TAG. Another factor that helps is colipase, an amphipathic protein that binds and anchors pancreatic lipase at the surface of the emulsion droplet.
Micelles
After digestion, monoglycerides and fatty acids associate with bile salts and phopholipids to form micelles. Micelles are about 200 times smaller than emulsion droplets (4-7nm versus 1µm for emulsion droplets). Micelles are necessary because they transport the poorly soluble monoglycerides and fatty acids to the surface of the enterocyte where they can be absorbed. As well, micelles contain fat soluble vitamins and cholesterol. The figure at right illustrates that micelles are small enough to fall between the the microvilli.
Absorption
Micelles are constantly breaking down and re-forming, feeding a small pool of monoglycerides and fatty acids that are in solution. Only freely dissolved monoglycerides and fatty acids can be absorbed, NOT the micelles. Because of their nonpolar nature, monoglycerides and fatty acids can just diffuse across the plasma membrane of the enterocyte. Some absorption may be facilitated by specific transport proteins (for instance see below, for cholesterol).
Answer:
A micelle is an aggregate of surfactant molecules dispersed in a liquid, forming a colloidal suspension. A typical micelle in water forms an aggregate with the hydrophilic "head" regions in contact with surrounding solvent, sequestering the hydrophobic single-tail regions in the micelle center
Micelle
Particle of colloidal dimensions that exists in equilibrium with the molecules or ions in solution from which it is formed.
Micelle (polymers)
Organized auto-assembly formed in a liquid and composed of amphiphilic macromolecules, in general amphiphilic di- or tri-block copolymers made of solvophilic and solvophobic blocks.
Note 1
An amphiphilic behavior can be observed for water and an organic solvent or between two organic solvents.
Note 2
Polymeric micelles have a much lower critical micellar concentration (CMC) than soap or surfactant micelles, but are nevertheless at equilibrium with isolated macromolecules called unimers. Therefore, micelle formation and stability are concentration-dependent.
Cross-section view of the structures that can be formed by phospholipids in aqueous solutions (unlike this illustration, micelles are usually formed by single-chain lipids, since it is difficult to fit two chains into this shape)
Scheme of a micelle formed by phospholipids in an aqueous solution
This phase is caused by the packing behavior of single-tail lipids in a bilayer. The difficulty filling all the volume of the interior of a bilayer, while accommodating the area per head group forced on the molecule by the hydration of the lipid head group, leads to the formation of the micelle. This type of micelle is known as a normal-phase micelle (oil-in-water micelle). Inverse micelles have the head groups at the centre with the tails extending out (water-in-oil micelle).
Micelles are approximately spherical in shape. Other phases, including shapes such as ellipsoids, cylinders, and bilayers, are also possible. The shape and size of a micelle are a function of the molecular geometry of its surfactant molecules and solution conditions such as surfactant concentration, temperature, pH, and ionic strength. The process of forming micelles is known as micellisation and forms part of the phase behaviour of many lipids according to their polymorphism.
Explanation:
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