An investigation into how temperature affects the rate of hydrolysis of starch by amylase.

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An investigation into how temperature affects the rate of hydrolysis of starch by amylase.

I am going to measure the rate of the disappearance of starch at different temperatures by observing the change in intensity of the blue colour formed by starch in iodine. The intensity of the blue colour is going to be proportional to the amount of starch present. The greater the change in absorbance between a sample of starch without enzyme (which is going to be my control) and the mixture containing the enzyme, the greater the amount of starch hydrolysed by the enzyme, therefore the greater the rate of reaction.

Prediction

I think that at 0°c the rate of reaction will be zero as I think no starch molecules will be hydrolysed, therefore the intensity of the blue colour is going to be the strongest when placed in iodine. After increasing the temperature from 0°c I think the rate of hydrolysis of starch will start to increase slowly then get faster, so that the rate of reaction doubles every 10°c. I think this will only happen up to 40°c, at which point the rate of hydrolysis of starch will be the fastest, therefore the intensity of the blue colour is going to be the weakest when placed in iodine as more starch will have been hydrolysed. After 40°c, I think the rate of hydrolysis of starch will begin to slow down rapidly and eventually stop completely at about 55°c, which again will produce the strongest intensity of blue colour when placed in iodine, as I think no starch will have been hydrolysed.

Scientific reasons for prediction

I think at 0°c the reaction between the amylase and starch molecules will not take place. This is because the amylase enzyme will become deactivated. Also I think both the amylase and starch molecules will not have the kinetic energy necessary to make collisions take place. This will mean that the substrate and enzyme can never bind to form the enzyme-substrate complex, so that no starch can be hydrolysed. The starch concentration will remain the same giving the most intensified blue colour when tested with iodine.

After 0°c I think the reaction rate, and therefore the hydrolysis of the starch by amylase will increase slowly. This is because at a low temperature the starch and amylase molecules will have a small amount of kinetic energy, and therefore will move relatively slowly. This means there will be less of a chance that the starch molecules collide with the active sites of the amylase, making binding between them infrequent. As temperature is increased further and further I think the rate of hydrolysis of starch will increase more and more. This is because a rise in temperature will give the amylase and starch molecules more and more energy making them move faster and collide more frequently. The enzyme-substrate complex will be formed more frequently hydrolysing more and more of the starch. In addition, more energy allows bonds to be broken more easily so that the reaction can take place.

I think each time the temperature is increased by 10°c, between 0°c and 40°c, the rate of reaction and therefore the rate of hydrolysis of starch will double. This is because every increase in 10°c will give the amylase and starch molecules twice as much kinetic energy than it had in the last 10°c. This will make the molecules move around twice as fast, doubling the chances of collisions taking place between the amylase and starch molecules. Therefore doubling the rate of formation of the enzyme substrate complex and the starch being hydrolysed. Once I have obtained all of my results and plotted the graph of rate of reaction against temperature, I will accurately check whether this part of my prediction is true by calculating Q10. This will be done using this equation.

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Q10 = rate of reaction at (× + 10)°c

          Rate of reaction at ×°c

If Q10 equals 2 then this will show that every 10°c rise in temperature does produce a doubling of the rate of reaction.    

I think the temperature at which the enzyme will work the fastest (optimum temperature), and therefore make the rate of hydrolysis of starch the fastest is going to be between 37°c and 40°c. I think this is because body temperature is around 37°c and enzymes are designed to work at their maximum output.

I think ...

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