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Chemistry Investigatory Project

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We would like to express our special thanks of gratitude to our respected Principal Mrs. Jayashree Khandekar for giving us this golden opportunity. Also a special thanks to our Chemistry teacher Mrs. Kritika. This project has helped us a lot to know more and to get more knowledge about the topic. The project required a lot of research and information. Finally, a word of thank to all those who helped us to do this project.

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Every health book insists on the chewing of food. The act of chewing stimulates the excretion of saliva. Saliva mixes up with the food and helps its digestion. That is, the enzyme ptyalin or amylase present in human saliva hydrolyses the big molecules of food into many molecules. Amylase, like other enzymes, works as a catalyst. All catalysts are enzymes, but not all enzymes are catalysts. A catalyst is a substance that causes a chemical reaction to break down other substances, but the catalyst does not become a part of the end product of that reaction. Amylase digests starch by catalyzing hydrolysis, which is splitting by the addition of a water molecule. Therefore starch plus water becomes maltose (which is equivalent to two joined glucose molecules). Body temperature is the optimal heat for the best reaction of amylase.

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To Study the Digestion of Starch by Salivary Amylase

and Effect of pH and Temperature on it.

Structure of salivary amylase

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Test tubes Test tube stand One dropper Beaker Stop watch Starch and Iodine solution Thermometer Dil. HCl and Dil. NaOH solution.

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1) Collection of Saliva - Rinse mouth thoroughly with cold water and ensure that it does not contain any food particles. Now take about 20ml of Luke warm water in the mouth and gargle for about three minutes so that saliva mixes up well with it. Spit this into a beaker. Filter, if there is any suspended impurity clear filtrate is saliva solution and contains enzyme ptyalin.

2) Preparation of starch solution - Take about 0.5g of starch in a 100ml beaker and add enough water to make a paste. Dilute the paste by adding 50ml water and boil for about 5 min.

3) Digestion of starch (a) takes 5ml of the starch solution in a test tube. Add 2 ml of saliva solution into it. Mix the solutions well by shaking the tube carefully and start a step watch. (b) After one minute take out two drops of the mixture solution from the test tube with the help of a dropper and transfer it into another test tube containing about one ml of 1% iodine solution. Note the colour produced, if any. (c) Repeat this test after every one minute taking two drops of the mixture solution and fresh 1% iodine solution continue until the test shows no blue colour. Record the time and blue colour intensity.

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(1.)Effect of temperature on the digestion of starch by saliva.

Take three test tubes and label these 1, 2, and 3.

Take 5ml of the starch solution, 2ml of the saliva solution and 5 ml of water in each test tube.

Place test tube No. 1 in water at room temperature, test tube No.2 in a beaker containing water at 500 C and test tube No.3 in boiling water.

After 5 minutes, observe the colour change on mixing two drops of the mixture of every tube with one ml of 1% iodine solution. Note the intensity of blue coloured form.

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Conclusion-Starch gets hydrolyzed by saliva amylase.

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(2)To study the effect of pH on the salivary digestion of starch.

Take three test tubes and label these 1, 2 and 3.

Add 5ml of the starch solution, 2ml of the saliva solution in each test tube.

Now add 2 ml of water inn test tube No. 1, 2 ml of dil. HCl in test tube No. 2 and 2ml of dil. NaOH solution in test tube No. 3 and shake carefully.

Keep the three test tubes in water at room temperature for about 10 minutes.

Add two drops of the solution of each test tube with 1% iodine solution and observe the colour change.

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Temperature affects the digestion of starch by saliva. With increase in temperature salivary amylase gets inactivated and process of digestion does not take place.

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Enzymes cause various reactions in the body to happen, also called diastase. Things that we eat are broken down once in the mouth organ. Amylase is an enzyme that breaks down starch to sugar. The amylase in the mouth, salivary amylase, is called ptyalin. Ptyalin can do digestive can work in the stomach for several hours. Iodine and Benedict’s solution is used to recognize starch and sugar (maltose) in our saliva.

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Further, enzymes and their activity are very sensitive to temperature and pH. Even a slight variation in these two factors, can disrupt the action of enzymes. In other words, digestion of food by salivary amylase is also effected by pH and temperature and can be verified experimentally. For example, hydrolysis of starch can be verified by testing it with iodine solution. Starch forms a blue coloured complex with iodine. If no starch is present in a system it will not give blue colour with iodine.

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Amylase is present in the saliva of humans and some other mammals, where it begins the chemical process of digestion. Foods that contain large amounts of starch but little sugar, such as rice and potatoes, may acquire a slightly sweet taste as they are chewed because amylase degrades some of their starch into sugar. The pancreas and salivary gland make amylase (alpha amylase) to hydrolyse dietary starch into disaccharides and trisaccharides which are converted by other enzymes to glucose to supply the body with energy. Plants and some bacteria also produce amylase. As diastase, amylase was the first enzyme to be discovered and isolated (by Anselme Payen in 1833). Specific amylase proteins are designated by different Greek letters. All amylases are glycoside hydrolyses and act on α-1,4-glycosidic bonds.

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1.α-amylases (alternative names: 1,4-α-D-glucan glucanohydrolase; glycogenase)

These are calcium metalloenzymes, completely unable to function in the absence of calcium. By acting at random locations along the starch chain, α-amylase breaks down long-chain carbohydrates, ultimately yielding maltotriose and maltose from amylose, or maltose, glucose and "limit dextrin" from amylopectin. Because it can act anywhere on the substrate, α-amylase tends to be faster-acting than β-amylase. In animals, it is a major digestive enzyme, and its optimum pH is 6.7–7.0.

In human physiology, both the salivary and pancreatic amylases are α-amylases.

The α-amylases form is also found in plants, fungi (ascomycetes and basidiomycetes) and bacteria (Bacillus).

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2.β-amylase (alternative names: 1,4-α-D-glucan maltohydrolase; glycogenase; saccharogen amylase)

This enzyme is also synthesized by bacteria, fungi, and plants. Working from the non-reducing end, β-amylase catalyzes the hydrolysis of the second α-1,4 glycosidic bond, cleaving off two glucose units (maltose) at a time. During the ripening of fruit, β-amylase breaks starch into maltose, resulting in the sweet flavor of ripe fruit.

Both α-amylase and β-amylase are present in seeds; β-amylase is present in an inactive form prior to germination, whereas α-amylase and proteases appear once germination has begun. Many microbes also produce amylase to degrade extracellular starches. Animal tissues do not contain β-amylase, although it may be present in microorganisms contained within the digestive tract. The optimum pH for β-amylase is 4.0–5.0.

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(Alternative names: Glucan 1,4-α-glucosidase; amyloglucosidase; Exo-1,4-α-glucosidase; glucoamylase; lysosomal α-glucosidase; 1,4-α-D-glucan glucohydrolase)

This enzyme will cleave α (1–6) glycosidic linkage, as well as the last α (1–4) glycosidic linkages at the non-reducing end of amylose and amylopectin, yielding glucose. The γ-amylase has most acidic optimum pH of all amylases because it is most active around pH 3.

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