Biological Importance of Shapes Fitting Together in Cells and Organisms

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There are many molecules within cells and organisms that must have complimentary shapes that fit together in order for them to carry out their function. One type of molecule for which this is extremely important is enzymes. There are two models that demonstrate how this may work, the first of which is the lock and key model in which the substrate and enzyme binding site have complimentary shapes so that the substrate or subtrates fit perfectly into the enzyme, which joins or separates them. The second model, the induced fit model, is similar, however the enzyme moulds its shape to match the substrate. There are many processes in which it is important that these shapes fit, for example DNA helicase, RNA polymerase and DNA polymerase must all have the correct shape in order for DNA strands to separate, mRNA to form and DNA to then rejoin during polypeptide synthesis. During polypeptide synthesis it is also important that Amino acyl RNA synthetase fits together with an amino acid and tRNA molecule in order to join them to form an amino acyl tRNA molecule, then for yet another enzyme to help form peptide bonds between amino acids. Another enzyme for which it is very important to have the correct shape is caspase. Caspases are involved in cell apoptosis, in which a cell kills itself. This usually happens after a cell reaches its hayflick limit, the limit in number of times it can divide, and becomes senescent. However, if the P53 gene, a tumour suppressor gene, becomes mutated, these caspases may form with a different tertiary structure, meaning that the cell will not undergo apoptosis and will continue to divide uncontrollably, resulting in a tumour. Yet another occasion in which enzymes and substrates must fit together is during digestion, in which maltase is required to break substances down into simple carbohydrates required in respiration. If lactase is an
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