Enzymes Speed



 How Enzymes Speed up the chemical Reaction?

A certain amount of energy is necessary to initiate any chemical reaction. This is called activation energy or free energy of activation. In a population of molecules of each substrate, the majority have average kinetic energy, some have higher and some lower than the average energy.  Under  normal temperature, only the molecules having relatively high energy are likely to react to form the product . Therefore, the reaction takes place very slowly. One way to make the reaction to go faster is to raise the temperature of the mixture. Heat increases the kinetic energy of the molecules, causing their collision and reaction. The other method to quicken the reaction is to add an enzyme. The enzyme lowers the activation energy of the reaction and allow a large number of molecules to react at a time. Exactly how the enzymes lower the activation energy is not clear. It is known that the enzymes combine with the substrate molecules and bring them close together which favours their collisions in the most suitable directions and location for the reaction to occur. The inorganic catalysts work in the same manner. It is now held that conformational changes in the active sites of the enzymes actually " Push" the substrate molecules toward an interaction.


 

   Chemical compounds undergo two types of changes. A physical change simply refers to a change in shape without breaking of bonds. This is a physical process. Another physical process is a change in state of matter: when ice melts into water, or when water becomes a vapour. These are also physical processes. When bonds are broken and new bonds are formed during transformation this will be called a chemical reaction. 

For example: 


is an inorganic chemical reaction . Similarly, hydrolysis  of starch into glucose is an organic chemical reaction. Rate of a physical or chemical process refers to the amount of product formed per unit time. It can be expressed as: 





Rate can also be called velocity if the direction is specified . Rates of physical and chemical processes are influenced by temperature among other factors. A general rule of thumb is that  rate double or decrease by half for every 10°C change in  either direction. Catalysed reactions processed at rates vastly higher than that of uncatalysed ones. When enzymes catalysed reactions are observed, the rate would be vastly higher than the same but uncatalysed reactions. 

For example



In the absence of any enzyme this reaction is very slow, with about 200 molecules of H2CO3 being formed in an hour. By using the enzyme present within the cytoplasm called carbonic anhydrase, the reaction speeds dramatically with about 600,000 molecules being formed every second. The enzyme has accelerated the reaction rate by about 10 million times. The power of enzymes is incredible indeed!

 There are thousands of types of enzymes each catalysing a unique chemical or metabolic reaction. A multistep chemical reaction, when each of the steps is catalysed by the same enzyme complex or different enzymes, is called a metabolic pathway.

For example:



is actually a metabolic pathway in which glucose becomes pyuvic acid though ten different enzymes catalysed metabolic reactions. When you study respiration will study these reactions. At this stage you should know that this very metabolic pathway with one or two additional reactions gives rise to a variety of metabolic end products.In our skeletal muscle, under anaerobic conditions, lactic acid is formed. Under normal aerobic conditions, pyruvic acid is formed .In yeasts, during fermentation, the same pathway leads to the production of ethanol ( alcohol). In different conditions different  products are possible. 

Information About Enzymes Formation:

It is surprising to know that over a thousand different chemical reactions occur at any given time in a cell having an average diameter of 20 ųm. Each of these reactions is catalysed by a specific enzyme. 

How does a cell know  which enzymes to produce? 

The DNA of each cell contains the information necessary for the production of all the enzymes it requires.  The cell uses this information as and when it needs enzymes for speeding up its specific reactions. The cell know which enzymes to produce though a process called gene expression. Gene expression refers to the process in which the information contained within a gene is used to synthesize a functional protein or enzyme. 

 The process of gene expression starte with DNA, which contains the genetic information of an organism.The DNA is transcribed into a molecule called messenger RNA ( mRNA) though a process called transcription. This step occurs in the nucleus of eukaryotic cells or directly in the cytoplasm of prokaryotic cells.

Once the mRNA is formed, it carries the genetic information from the DNA to the ribosomes, which are the cellular structure responsible for protein synthesis. The mRNA is then translated by ribosomes into a protein though a process called translation. 


 The sequence of nucleotides in the mRNA determines the sequence of amino acids form a three_ dimensional structure that determines the protein's function, such as an enzyme.The specific sequence of nucleotide in the sequence of nucleotides in the gene that was transcribed. 

In summary, cells know which enzymes to produce though the process of gene expression, where the information contained within specific  genes is transcribed into mRNA and then translated into proteins, including enzymes. The regulation of gene expression ensures that cells produce the right enzymes at the right time and in the right amount.










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