how it controle the reativity in the active site
216435
secondary coordination sphere plays a vital role in two ways; (1) it may give extra stability to the ligand through resonance after conjugation with the metal site through resonance , thus increasing the rate of conjugation with the metal. (2) it may also decrease the rate of conjugation with metal by causing steric inhibition.
228704
An enzyme is a protein that catalyzes, or speeds up, a chemical reaction. The word comes from the Greek ένζυμο, énsymo, which comes from én ("at" or "in") and simo ("leaven" or "yeast"). Certain RNAs also have catalytic activity, but to differentiate them from protein enzymes, they are referred to as RNA enzymes or ribozymes.\n\nEnzymes are essential to sustain life because most chemical reactions in biological cells would occur too slowly, or would lead to different products without enzymes. A malfunction (mutation, overproduction, underproduction or deletion) of a single critical enzyme can lead to a severe disease. For example, the most common type of phenylketonuria is caused by a single amino acid mutation in the enzyme phenylalanine hydroxylase, which catalyzes the first step in the degradation of phenylalanine. The resulting build-up of phenylalanine and related products can lead to mental retardation if the disease is untreated.\n\nLike all catalysts, enzymes work by providing an alternate pathway of lower activation energy of a reaction, thus allowing the reaction to proceed much faster. Enzymes may speed up reactions by a factor of many millions. An enzyme, like any catalyst, remains unaltered by the completed reaction and can therefore continue to function. Because enzymes do not affect the relative energy between the products and reagents, they do not affect equilibrium of a reaction. However, the advantage of enzymes compared to most other catalysts is their sterio-, regio- and chemoselectivity and specificity.\n\nEnzyme activity can be affected by other molecules. Inhibitors are naturally occurring or synthetic molecules that decrease or abolish enzyme activity; activators are molecules that increase activity. Some irreversible inhibitors bind enzymes very tightly, effectively inactivating them. Many drugs and poisons act by inhibiting enzymes. Aspirin inhibits the COX-1 and COX-2 enzymes that produce the inflammation messenger prostaglandin, thus suppressing pain and inflammation. The poison cyanide inhibits cytochrome c oxidase, which effectively blocks cellular respiration.\n\nWhile all enzymes have a biological role, some enzymes are used commercially for other purposes. Many household cleaners use enzymes to speed up chemical reactions ( e.g., breaking down protein or starch stains in clothes).\n\nMore than 5,000 enzymes are known. Typically the suffix -ase is added to the name of the substrate (e.g., lactase is the enzyme that catalyzes the cleavage of lactose) or the type of reaction (e.g., DNA polymerase catalyzes the formation of DNA polymers). However, this is not always the case, especially when enzymes modify multiple substrates. For this reason Enzyme Commission or EC numbers are used to classify enzymes based on the reactions they catalyze. Even this is not a perfect solution, as enzymes from different species or even very similar enzymes in the same species may have identical EC numbers.\nIn enzymes, as with other proteins, function is determined by structure. An enzyme can be:\n\n    * A monomeric protein, i.e., containing only one polypeptide chain, typically one hundred or more amino acids; or\n    * an oligomeric protein consisting of several polypeptide chains, different or identical, that act together as a unit.\n\nAs with any protein, each monomer is actually produced as a long, linear chain of amino acids, which folds in a particular fashion to produce a three-dimensional product. Individual monomers may then combine via non-covalent interactions to form a multimeric protein. Many enzymes can be unfolded or inactivated by heating, which destroys the three-dimensional structure of the protein.\n\nhttp://en.wikipedia.org/wiki/Enzyme#3D_Structure
288739
Amount of enzyme\nAmount of substrate\nAmount of any cofactors, that might be involved in the reaction.\n\nFor some reversible reactions, even amount of product can drive the reaction in reverse!\n\nAny of these factors can change.  Cells often translate extra enzyme, to increase enzyme activity.
85769
Proteins exist as a linear chain of amino acids. This chain can degrade over time as such a reaction is thermodynamically favorable in an aqueous environment (recall that proteins are synthesized by using energy to drive off a water molecule to form the peptide bond). When proteins degrade over time, this is called protein-turnover. It is the balance between a protein's degradation and its synthesis that determines the concentration of that protein inside the cell.\n\nStudies of protein turnover rates have shown that some proteins are short-lived while others are long-lived. Long-lived proteins constitute the majority of proteins in the cell. Short-lived proteins are typically key regulatory proteins and abnormal proteins (abnormal proteins are often partially unfolded and as we saw in our discussion of chaperones, such proteins are prone to degradation).\n\nUb functions to regulate protein turnover in a cell by closely regulating the degradation of specific proteins. Such a regulatory role is very important. By regulating protein degradation, cells can quickly eliminate a protein that in turn regulates another function (like a transcription factor that is needed to express a particular gene). Furthermore, this form of control is very effective as the elimination of a particular regulatory protein ensures that the process expressed by the regulatory protein is shut-down. An alternative regulatory strategy used by cells is to simple inactivate proteins (by changing their conformation). Unlike the Ub-linked regulation, such inactivated proteins can mistakenly be reactivated. Of course, Ub-linked regulation is energetically expensive, for if a regulatory protein is needed again, it has to be re-synthesized.
110382
B, its specific shape allows specific substrates to bind to the enzyme, thus catalyzing the reaction. If the enzyme DIDN'T have the specific shape, then the substrate would have to take a longer time to break their own bonds themselves.
202712
Okay, cool!\nThe diagram is set up so that on the horizontal x-axis is the "reaction coordinate," which is basically just time as the reaction proceeds.  The vertical y-axis is energy.  \n\nThe potential energy of the reactants is where the graph curve starts, touching the y-axis.  The potential energy value is the y-value at this location.  \n\nWhere the graph curve levels off at the end is the products, so the potential energy of the products is the y-value where the curve levels off.  \n\nThe activation energy is how much energy had to be added into the system to get to the activated complex, located at the peak of the diagram's curve.  Take the y-value at the top of the curve and subtract from the the potential energy of the reactants.  \n\nThe heat of reaction is the difference in the potential energies of the products and reactants.  Take the potential energy of the products, and subtract from that the energy of the reactants.  \n\nIf a catalyst were added, the potential energy of the products and reactants remain unchanged, but the activation energy is less, so you draw a curve that starts in the same place and ends in the same place as the original diagram, but your curve just won't go up as high.  The hill for a catalyst is less steep.
411037
My guess would be that the larger the particle, the slower the reaction, as the particle would have to achieve an orientation that would fit within the active site of the enzyme, and the larger the particle, the longer it would take for it to orient itself to fit in.
635129
This is not a simple question.  Some hormones, once they activate the receptor are endocytosed with the receptor into the cell.  Therefore, these hormones can only activate the receptor one time.\n\nOther hormones activate receptors inside the cells (e.g. steroid hormones) and again, may stay attached to the receptor as it translocates to the nucleus to activate gene expression.\n\nLastly, still others may activate a surface receptor and then dissociate from the receptor, making them available to activate the receptor again.\n\nHope this was helpful.   If you go to Pubmed (enter "entrez pubmed" in your search engine), they have access to many online medical texts on cell biology.  You can search these books for their chapters and info. on hormones, receptors, etc.\n\nBest wishes.
144856
It is a chemical reaction.
361747
Experimentally you can do primer extension, which will show the +1 site, from there you can identify the RBS and -10 and -35 sequences.\n\nYou can also do mobility shift assays with RNA polymerase to show that a certain piece of DNA contains the promoter, then do DNAse protection assays to show where the polymerase is actually binding.
134064
(m)\n\nmetabolic pathway analysis, it should be considered that many enzymes operate with low specificity (e.g. nucleoside diphosphokinase, uridine kinase, transketolase, aldolase), so that various substrates and products can be converted. Here, we analyze the effect of enzymes with low substrate specificity on the elementary flux modes (pathways). We also study the benefits of two different approaches to describing multifunctional enzymes. The usual description is in terms of (overall) enzymatic reactions. At a more detailed level, the reaction steps (half-reactions, hemi-reactions) of the formation and conversion of enzyme-substrate complexes are considered. Multifunctional enzymes operate according to various mechanisms. This is illustrated here by the reaction schemes for the different enzyme mechanisms of bifunctional enzymes. For enzymes with two or more functions, it is important to consider only linearly independent functions, because otherwise cyclic elementary modes would occur which do not perform any net transformation. However, the choice of linearly independent functions is not a priori unique. We give a method for making this choice unique by considering the extreme pathways of the hemi-reactions system. A formal application of the algorithm for computing elementary flux modes (pathways) yields the result that the number of such modes sometimes depend on the level of description if some reactions are reversible and the products of the multifunctional enzymes are external metabolites or some multifunctional enzymes partly share the same metabolites. However, this problem can be solved by appropriate interpretation of the definition of elementary modes and the correct choice of independent functions of multifunctional enzymes. The analysis is illustrated by a biochemical example taken from nucleotide metabolism, comparing the two ways of description for nucleoside diphosphokinase and adenylate kinase, and by several smaller examples.
151216
It's the least reactive. It's non-polar. It's pKa is simply the average of the N and C terminus. It's also Ambivalent, meaning it can be inside and outside a protein. Because of these properties, if it was replaced with a polar AA, it would change the protein property, and in 99% of time, change in AA is deleterious.
538366
The ligand will accomodate electrons from the ligands, forming dative bonds.\n\nThe sub-shell also ceases into two groups of orbitals.  One group will be at a higher energy level as compared with the other.  The difference in energy level is acounted by the strength of the ligand, in other words, by its polarising power.  The stronger the ligand, the greater is the energy difference between the two groups of orbitals.
200118
Enzymes are very sensitive to their environment. The acidic environment denatures the enzyme (causes the enzyme to change its shape by destroying some vital chemical bonds that constrain it into the proper shape) Most enzymes are like the toys toddlers play with to learn their shapes. The square only fits the square opening--the same principle applies here. Once an enzyme loses its shape it loses its function.
437693
At physiological pH most of the -COOH of amino acids are deprotonated (-COO-) and -NH2 protonated (-NH3+).\nIf you increase the pH then the -COO- will remain as such but the -NH3+ will lose the proton. -NH3+ can act only as an H-donor for an H-bond so such a bond will be broken. However if the geometry and number of interacting partners allow it it could be replaced by another H of the same -NH2 group.\n\nTyrosine has pKa around 10, so if you go to extremely basic pH it will be deprotonated and thus it will not be able to act anymore as an H-donor for a hydrogen bond and the bond will break. If however it was acting as a lone pair donor, the bond will become even stronger.\n\nGenerally when the pH change (extremely basic or acidic) causes changes in the charge of the group can but not necessarily breaks H-bonds. An important note: even if the H-bonds are not completely broken there will be rearrangement (some bonds might break and others form as the some H-donors become H-acceptors and vice versa) changing the conformation/folding of the protein.\n\nFor sure the effect of pH on ionic bonds is far greater than that on H-bonds.
449778
Using the Michaelis-Menten equation.\n\nMore details on teh attached link\n\nhttp://www.le.ac.uk/by/teach/biochemweb/tutorials/michment2print.html\n\nGood luck
342047
If the Catalyst is inorganic the higher the temp the quicker it works, if the catalyst is organic(enzyme),it will reach a peak of activity,then further temp will destroy the catalyst