Induced Fit : According to the induced fit model, both enzyme and substrate undergo dynamic conformational changes upon binding. The enzyme contorts the substrate into its transition state, thereby increasing the rate of the reaction. When an enzyme binds its substrate, it forms an enzyme-substrate complex. This complex lowers the activation energy of the reaction and promotes its rapid progression by providing certain ions or chemical groups that actually form covalent bonds with molecules as a necessary step of the reaction process.
Enzymes also promote chemical reactions by bringing substrates together in an optimal orientation, lining up the atoms and bonds of one molecule with the atoms and bonds of the other molecule. This can contort the substrate molecules and facilitate bond-breaking. The active site of an enzyme also creates an ideal environment, such as a slightly acidic or non-polar environment, for the reaction to occur. The enzyme will always return to its original state at the completion of the reaction.
One of the important properties of enzymes is that they remain ultimately unchanged by the reactions they catalyze. After an enzyme is done catalyzing a reaction, it releases its products substrates. Cellular needs and conditions vary from cell to cell and change within individual cells over time. For example, a stomach cell requires a different amount of energy than a skin cell, fat storage cell, blood cell, or nerve cell.
The same stomach cell may also need more energy immediately after a meal and less energy between meals. Because enzymes ultimately determine which chemical reactions a cell can carry out and the rate at which they can proceed, they are key to cell functionality.
The cell uses specific molecules to regulate enzymes in order to promote or inhibit certain chemical reactions. Sometimes it is necessary to inhibit an enzyme to reduce a reaction rate, and there is more than one way for this inhibition to occur.
In noncompetitive inhibition, an inhibitor molecule binds to the enzyme at a location other than the active site an allosteric site. The substrate can still bind to the enzyme, but the inhibitor changes the shape of the enzyme so it is no longer in optimal position to catalyze the reaction.
Enzyme inhibition : Competitive and noncompetitive inhibition affect the rate of reaction differently. Competitive inhibitors affect the initial rate, but do not affect the maximal rate, whereas noncompetitive inhibitors affect the maximal rate. In noncompetitive allosteric inhibition, inhibitor molecules bind to an enzyme at the allosteric site.
The binding of this allosteric inhibitor changes the conformation of the enzyme and its active site, so the substrate is not able to bind. This prevents the enzyme from lowering the activation energy of the reaction, and the reaction rate is reduced. However, allosteric inhibitors are not the only molecules that bind to allosteric sites.
Allosteric activators can increase reaction rates. This increases the reaction rate. Allosteric inhibitors and activators : Allosteric inhibitors modify the active site of the enzyme so that substrate binding is reduced or prevented.
In contrast, allosteric activators modify the active site of the enzyme so that the affinity for the substrate increases. Enzymes are highly selective catalysts, meaning that each enzyme only speeds up a specific reaction. The molecules that an enzyme works with are called substrates. The substrates bind to a region on the enzyme called the active site.
In the lock-and-key model, the active site of an enzyme is precisely shaped to hold specific substrates. Two reactants might also enter a reaction, both become modified, and leave the reaction as two products. Since enzymes are proteins, this site is composed of a unique combination of amino acid residues side chains or R groups. Each amino acid residue can be large or small; weakly acidic or basic; hydrophilic or hydrophobic; and positively-charged, negatively-charged, or neutral.
The positions, sequences, structures, and properties of these residues create a very specific chemical environment within the active site. A specific chemical substrate matches this site like a jigsaw puzzle piece and makes the enzyme specific to its substrate. Increasing the environmental temperature generally increases reaction rates because the molecules are moving more quickly and are more likely to come into contact with each other. However, increasing or decreasing the temperature outside of an optimal range can affect chemical bonds within the enzyme and change its shape.
If the enzyme changes shape, the active site may no longer bind to the appropriate substrate and the rate of reaction will decrease. Dramatic changes to the temperature and pH will eventually cause enzymes to denature. This model asserted that the enzyme and substrate fit together perfectly in one instantaneous step.
However, current research supports a more refined view called induced fit. When an enzyme binds its substrate, it forms an enzyme-substrate complex.
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