Starch and Amylase

A key to the following chart

showing the true colours of the tested solutions

Table 1. A table showing the colour of each test solution when

recorded at two minuet intervals

The results featured in Table 1. have also been presented in graph format on the following page.

Conclusion

During the year 1835 Anselme Payen and Jean Persoz first discovered the chemical substance known as amylase while conducting a malt purification experiment. Although they could not explain the exact role of amylase they theorised that it was essential for certain biochemical processes. There are two major types of amylase which both function to catalyse the hydrolysis of starch, glycogen or dextrin. Hydrolysis occurs when a molecule is split up by the addition of another polar water molecule. Alpha amylase found in normal human saliva is termed ptyalin and is responsible for the first stages of chemical digestion. Ptyalin initiates the brake down of polysaccharides, such as starch, found in food as they enter the mouth. Starch is a polymer, a chain of amino acids that are linked together by glycosidic bonds and salivary amylase interrupts the bonding process to form many double units. The double glucose units are referred to as maltose, a substance that is utilised by the body in the formation of energy. Ptyalin may continue working inside the stomach for many hours and can digest up to 40% of starch under the correct conditions of food solidity and stomach acidity. The other major variety of amylase is amylopsin, sometimes called pancreatic amylase as it is secreted in pancreatic juices located in the small intestine. Other enzymes produced by the body then further digest the maltose and glucose units, and then absorb the remaining material through the walls of the small intestine to be used as energy.

Amylase functions as a biological catalyst and is a common enzyme. Enzymes speed up chemical reactions and reduce the need for an increase in temperature, (in order to speed up reactions), within living things. Such a general rise in body temperature would typically be lethal to the organism. An enzyme has an active site, which has a unique shape into which only a substrate of the exact same unique shape can fit. When this substrate fits into the active site it forms an enzyme-substrate complex. The unique partner of salivary amylase enzyme, also known as Ptyalin, is starch.

The aim of the experiment was to determine the effect of temperature on the efficiency of amylase to brake down starch. An increase in temperature may affect the rate at which amylase can brake down starch in two ways. Increases in temperature also increase the kinetic energy of the substrate and enzyme molecules, making them move around faster. The faster the molecules move around, (faster Brownian motion), the more likely they are to collide with each other, resulting in an overall increase in the rate of reactions. It is stated that a 10˚C rise in temperature approximately doubles the rate of reaction. The results from the experiment do not support this part of the collision theory, as the amount of starch present increases as temperature levels rise, showing an overall decrease in amylase activity. The test solution maintained at 100˚C was shown to have contained the highest amount of starch, and therefore lowest amylase activity. The enzyme did not appear to function effectively at temperatures above 40˚C, and seemed to work best at lower temperatures, around 22˚C. The collision theory also states that as temperatures increase, so does particle vibration. As temperatures rise the bonds holding the enzyme together may shake apart, and change the shape of the molecule. If the shape of the enzyme alters significantly the substrates can no longer bind with the active site, and the molecule ceases to function. This part of the theory may best explain the results from the experiment. As the temperature increased above 22˚C, the increased vibrations may have shaken the amylase structure and altered the active site shape, so slowing the rate of reactions. By the temperature 100˚C, every amylase molecule had altered so much that they had all denatured. In conclusion, the experiment demonstrated that when amylase was exposed to temperatures above 40˚C the rate of reaction reduced drastically. Although chemically, a temperature rise increases the number of particle collisions, it also increases the likelihood of the brake down of the three dimensional structure of the enzyme molecule. It was not possible to obtain the exact optimum temperature for amylase function from the experiment, however it is assumed to be around 37˚C, normal human body temperature.

References

Taylor, D.J., et al. 2000. Biological Science 1 & 2. 3rd edition. Cambridge University Press. Pages 82-89, 188-122.

Jones, Alan., et al. 1999. Access to Chemistry. The Royal Society of Chemistry. Pages 237-239.

http://www.bartleby.com/65/am/amylase.html

Graph 1. A graph displaying the amount of starch present in each test droplet taken at two minuet intervals from all of the test tubes containing amylase solutions at

various temperatures.