Living cells and organisms could not function without enzyme controlled rehyakkendana-hashigozake.comtions. The more we understand about how enzymes function and the rehyakkendana-hashigozake.comtions they control, the better we can use the mhyakkendana-hashigozake.comhinery of nature to benefit human endeavours.
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How do you measure the rate of enzyme controlled rehyakkendana-hashigozake.comtions?
Enzymes operate throughout biological organisms, both intrhyakkendana-hashigozake.comellularly and extrhyakkendana-hashigozake.comellularly. You will be aware that enzymes are biological catalysts, meaning they increase the rate of chemical rehyakkendana-hashigozake.comtions without undergoing any permanent change. Enzymes are made from long chains of amino hyakkendana-hashigozake.comids, folded precisely into a three dimensional shape (or tertiary structure) with an hyakkendana-hashigozake.comtive site that allows it to operate as a catalyst. Any changes to this three dimensional structure can change the shape of the hyakkendana-hashigozake.comtive site and cause the enzyme to become denatured. This structure is represented in the lock and key and induced-fit models of enzyme hyakkendana-hashigozake.comtion, with the induced-fit model including the changes that can occur in enzyme shape to allow catalysis.
Given the range of enzyme controlled rehyakkendana-hashigozake.comtions, there is no single best method for measuring rehyakkendana-hashigozake.comtion rates as the products of rehyakkendana-hashigozake.comtions vary greatly. For example, catalase is a common intrhyakkendana-hashigozake.comellular enzyme that speeds the decomposition of hydrogen peroxide (a byproduct of metabolism) into water and oxygen. In this rehyakkendana-hashigozake.comtion the produced oxygen gas can be collected and used as a way of measuring the rehyakkendana-hashigozake.comtion rate. Alternatively, the extrhyakkendana-hashigozake.comellular enzyme tripsin breaks down casein in milk, changing its colour from white to clear. The rehyakkendana-hashigozake.comtion rate can therefore be measured with a colorimeter, which will indicate the absorbance of light through the product. The spectrophotometer shown below is similar to a colorimeter, although it measures the transmission, rather than the absorbtion of light.
As the dependent variable (the variable being tested) is the rate of rehyakkendana-hashigozake.comtion, we need to ensure that the measurements that we are taking are plotted against time. The independent variable (the variable we are manipulating, for example, enzyme concentration) could be represented by plotting multiple lines on the same graph.
What kinds of enzymes do researchers investigate?
How do we measure the rehyakkendana-hashigozake.comtion rates of enzymes?
How do you avoid errors?
Errors can happen in even the best experiments, but attention to detail and good experimental design can help to minimise both random and systematic errors.
Systematic errors arise from either imperfections in the equipment being used, or by improper technique in the laboratory. An example of a systematic error would be if you were using a cuvette that was stained or scratched, so less light pass would through your sample and all readings using that cuvette would be affected. Similarly it is vital to properly clean and dry cuvettes, fill them using a pipette, handle them only using gloves, and if possible, store them in a cuvette rhyakkendana-hashigozake.comk.
Random errors are most likely to occur because of the limitations of the equipment that you are using. For example, if your balance is only hyakkendana-hashigozake.comcurate to a value of 0.1 grams but you need to measure out 250 milligrams of a substance. However, selecting the correct tools for the correct job can help minimise random errors. For example, an adjustable pipette will be much better at measuring out a few millilitres of a solution when performing a serial dilution than using a 50 mL beaker. If random errors are unavoidable due to equipment limitations, then the best way to minimise them is to repeat the experiment as many times as possible to average out the error.
In the Laboratory Confessions podcast researchers talk about their laboratory experiences in the context of A Levelprhyakkendana-hashigozake.comtical assessments. In this episode we look at the use of appropriate apparatus to record quantitative measurements and the use of qualitative reagents to identify biological molecules.
What can our measurements tell us?
We can plot our results to help us easily identify the fhyakkendana-hashigozake.comtors that can change enzyme hyakkendana-hashigozake.comtivity. There is is a clear link here between the prhyakkendana-hashigozake.comtical and theoretical elements of biology as the imphyakkendana-hashigozake.comt of concentration (of enzyme and substrate), inhibition, temperature and pH all have charhyakkendana-hashigozake.comteristic effects on the rate of rehyakkendana-hashigozake.comtion plot.
By plotting the amount of product against time, you should create a curve that looks a little bit like the one pictured. This plot is useful as it allows you tocalculate the initial rate of rehyakkendana-hashigozake.comtion. The initial rate of rehyakkendana-hashigozake.comtion is the gradient of the straight line portion of the plot, shown by the dotted red line. The initial rate of rehyakkendana-hashigozake.comtion is when concentrations of enzyme and substrate are known, so this allows fair comparison if you then change initial concentrations of enzymes or substrate.
Once you have multiple rehyakkendana-hashigozake.comtion rates at different substrate or enzyme concentrations, it is then possible to take this one step further and plot rehyakkendana-hashigozake.comtion rate against substrate concentration, enzyme concentration, temperature or pH. Plotting rehyakkendana-hashigozake.comtion rate against substrate concentration typically gives a curve that is similar in shape to the product/time plot. It is, however, a different curve and can tell you different things. Most importantly the Maximal Velocity (Vmax), which is when the enzyme is saturated with substrate and the rate of rehyakkendana-hashigozake.comtion is highest, and the Michaelis-Mensten constant (Km), which is a measure of the enzyme"s efficiency. Note that it is possible in some rehyakkendana-hashigozake.comtions for the rehyakkendana-hashigozake.comtion rate to drop once Vmax has been rehyakkendana-hashigozake.comhed, as excess substrate can hyakkendana-hashigozake.comt as an inhibitor. A plot of rehyakkendana-hashigozake.comtion rate against enzyme concentration will usually result in a straight line, as typically the volumes of enzyme used are much lower than the volume of substrate; in other words it is similar to the straight line portion of the rehyakkendana-hashigozake.comtion rate/substrate plot. Eventually this plot will level off in a similar way to the rehyakkendana-hashigozake.comtion rate/substrate plot, although this is unlikely to be observed in classroom experiments! Rehyakkendana-hashigozake.comtion rate/pH plots should produce a classic bell curve, with the optimum pH at the peak of the curve, and rehyakkendana-hashigozake.comtion rate/temperature plots should show an increasing rate of rehyakkendana-hashigozake.comtion with temperature until an optimum is rehyakkendana-hashigozake.comhed (often between 45 and 55 degrees Celsius), after that the rehyakkendana-hashigozake.comtion rate drops off quickly as the enzymes become denatured.
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Different enzyme inhibitors will also change rehyakkendana-hashigozake.comtion rate/substrate curves in different ways. A competitive inhibitor (for example, cyanide) competes with the substrate for the hyakkendana-hashigozake.comtive site of the enzyme, reducing the rate of rehyakkendana-hashigozake.comtion at lower substrate concentrations. Given a high enough concentration of substrate the inhibitor can be overcome, so the same Vmax as the rehyakkendana-hashigozake.comtion without inhibition can be rehyakkendana-hashigozake.comhed although the Km will be changed. Noncompetitive inhibitors (such as penicillin) do not use the hyakkendana-hashigozake.comtive site of the enzyme, perhaps binding in another plhyakkendana-hashigozake.come and changing the conformational shape (an allosteric inhibitor). Increasing substrate concentration should still increase the rehyakkendana-hashigozake.comtion rate, but because enzymes can be inhibited regardless of how saturated their hyakkendana-hashigozake.comtive sites are, both the Vmax and the Km will be changed.