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    Thought it would be good to have one thread where we can all share examples of synoptic essays and, if you know, what marks they achieved

    Good luck for June everyone
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    The Importance of shapes fitting together in cells and organisms

    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 incorrect shape due to mutation, this can result in lactose intolerance, in which lactose cannot be digested.
    Enzymes however are not the only molecules for which it is important for shapes to fit together, another being antigens and antibodies. When a bacteria enters the body it has antigens on its surface that are recognised by the white blood cells. B-Lymphocytes, with the help of T-Helper lymphocytes, produce antibodies with shapes complimentary that of the antigens, causing them to bind together. These antigens may then cause the antigens to join ready to be engulfed by a phagocyte, may cause lysis in which the cell membrane breaks, or may neutralise the toxins produced by the bacteria. The antibodies can however also attack some of the bodies own cells, known as an autoimmune disease, which can result in problems such as diabetes.
    Another two molecules whose shapes must fit together are hormones and receptors, which join to form a hormone receptor complex, stimulating a chemical change within a cell, known as the second messenger model. If the receptor loses its receptiveness it can cause diseases such as type 2 diabetes where the insulin receptors and insulin can no longer form a complex.
    It is also important that the shapes of red blood cells and oxygen can fit together, so that oxygen can be carried to cells for respiration. This happens due to the biconcave structure of red blood cells which means it can associate with two molecules of oxygen.
    Actin and Myosin must also fit together during the sliding filament mechanism of muscle contraction, in which the myosin head fits into the actin binding site and pulls it along, using ATPase to hydrolyse the ATP, providing energy.
    If a gene is not expressed it is due to an inhibitor attached to the transcriptional fact, whose shape must fit perfectly. However, if there is an oestrogen receptor, that's shape will fit an oestrogen molecule, oestrogen can bind to it, changing the shape and releasing the inhibitor.
    In conclusion, within cells and organisms the shapes of different substances have an extremely important link to their function, and even a slight change in shape can have a very significant effect on the cell, or organism as a whole.
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    Do you reckon you should talk about how molecules stop being complimentary (e.g. mutation in amino acid sequence) as an intro or conclusion or not at all? not sure if it is a bit off topic
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    (Original post by Type 1)
    Do you reckon you should talk about how molecules stop being complimentary (e.g. mutation in amino acid sequence) as an intro or conclusion or not at all? not sure if it is a bit off topic
    Think i could have had a couple more marks if I had mentioned that at some point going by the examiners report
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    (Original post by Beth_L_G)
    Think i could have had a couple more marks if I had mentioned that at some point going by the examiners report
    Ahhh okay well you have made some good points, more than I could think of, so I might steal a few
 
 
 
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