Example research essay topic: Rate Of Reaction Hydrogen Bonding - 2,165 words

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RESEARCH I know that Rennin is an enzyme, so before conducting this experiment I am first going to do some research into enzymes and their effects. 1. Enzymes Enzymes are large globular molecules of which the vast majority are protein in nature, though some, known as 'ribozyme's' are made of RNA. Enzymes have catalytic properties; in other words, they alter the rate of reaction without themselves undergoing a permanent change. Most chemical reactions require an initial input of energy, called activation energy, to enable them to occur. Enzymes reduce the need for activation energy and so allow reactions to take place more readily and at lower temperatures than would otherwise be necessary. This can be seen in the graphs. 2.

Enzyme Action Enzymes, as biological catalysts, can be used in both anabolism (the build up of simple chemicals into complex ones) and catabolism (the breakdown of complex chemicals into simpler ones), although the latter is more common especially in the animal digestive system. As shown in the next diagram it is thought that the substrate molecules fit precisely into the enzyme molecules. This theory is referred to as the lock and key mechanism. However, in practice, it is likely that the enzyme itself to some extent is the substrate. The part of the enzyme molecule into which the substrate fits is called the active site. The configuration of the enzyme is due to ionic bonding, hydrogen bonding, disulphide bridges and hydrophobic interactions. 3.

Specificity The substrate molecule makes a precise fit into the active site and though the enzyme may be flexible up to a point, the number of molecules which can fit into the active site is very small - in fact it is often limited to just one type. Therefore enzymes are specific to one type of reaction. 4. Reversibility Enzymes can catalyst the forward and reverse reactions equally. 5. Temperature As temperature increases, the molecules, according to the 'Kinetic Theory' move faster, due to increased energy. Therefore, the enzyme and substrate molecules will meet more often and the rate at which the product is formed will increase. However, as the temperature continues to rise the hydrogen and ionic bonds, which hold the enzyme in shape, break and the active site will no longer accommodate the substrate.

The enzyme is then said to be denatured - this cannot be reversed. 6. pH Efficient functioning of an enzyme depends upon the shape of its active site. This shape is determined, in part, by ionic and hydrogen bonding - which can be affected by pH. Therefore every enzyme has its optimum pH, when its substrate fits exactly into its active site. Variation of pH will denature the enzyme. 7.

Other Factors which could Affect the Rate of an Enzyme Inhibitors compete with the substrate for the active sites of enzymes. They are known as competitive inhibitors. The greater the concentration of the substrate the more likely it is to occupy the active sites and the less the effect of the inhibitor. Non-competitive inhibitors attach themselves to the enzyme at a site other than the active site. However, in doing so they alter the shape of the active site in such a way that the substrate cannot fit into it and the enzyme cannot function. As the substrate and inhibitor are not competing for the same site, an increase in substrate concentration does not diminish the effect of the inhibitor. 8.

Rennin Rennin is a proteolytic enzyme and is characteristically found in the gastric juices of young mammals. It is one of only two enzymes (the other being pepsin) to be produced in the stomach. Rennin is secreted in an inactive form, pro-rennin, which is activated by the hydrochloric acid of the gastric juice. Rennin catalyses the conversion of the protein of milk, caseinogen, into paracasein, which is precipitated in the stomach as a calcium salt. The precipitated paracasein forms a firm curd in the stomach, which ensures that milk stays for some time in the stomach so that it becomes exposed to the actions of the proteolytic enzymes and the acid in the gastric juice.

REFERENCES For my research, I used 'Letts Study Guide' by Glenn and Susan Toole and 'Biology of the Mammal' by P. Catherine and Arthur G. Clegg. MY INVESTIGATION The factors that affect the enzyme rennin which I am going to investigate are: Temperature pH Concentration of enzyme PREDICTIONS 9. Temperature How will temperature affect the rate at which rennin acts on milk? The Kinetic Theory states that with increased temperature, molecules receive more energy, resulting in them speeding up their movement.

If the milk and the rennin molecules are moving faster, they will collide more often. The collisions will also have more energy so more of them are successful. Therefore the rate of reaction increases. However, above 37 C, which I believe is rennin's optimum working temperature, because this is body temperature, and rennin is found within the stomach of young mammals; I predict that the rate of reaction will decrease. This is because the rising temperature affects the hydrogen and ionic bonds which determine the shape of the enzyme. As these bonds are broken the shape of the active site changes and the molecules of caseinogen can no longer occupy them.

The rennin is now denatured and the rate of reaction will become zero. This is irreversible. If the temperature falls below 37 C, according to the Kinetic Theory the enzyme and substrate molecules will not be receiving as much energy, and therefore their movement will slow down. This will reduce the number of collisions between the rennin and the caseinogen, and there is a higher probability that these collisions will be unsuccessful due to the lack of energy. Therefore the rate of reaction will reduce.

At 0 C I still suspect the rennin to catalyst the conversion of caseinogen to paracasein, but it will take a lot longer. I predict that to stop the reaction altogether it would have to be at absolute zero (- 273 C) when Scientists predict that there would not be enough energy for the movement of any molecule at all. The graph shows how my prediction of how temperature will affect the rate of rennin. The actual rate of reaction that will take place will be a balance between the two opposing influences of greater kinetic movement of molecules increasing the rate and the decreasing rate due to denaturation of the rennin. 10. pH How will the pH affect the rate at which rennin acts on milk?

I know from my research that rennin is produced in the stomach and is activated by the gastric juice. The gastric juice contains much hydrochloric acid, and therefore I predict that rennin will work to its optimum around pH 1. Variation from this pH, I believe will slow the rate of reaction because the differing pH will affect the ionic and hydrogen bonding which determine the shape of the enzyme. When the active site of rennin is affected, the molecules of caseinogen will not be able to fit precisely into the site and therefore less or no product will be produced, and therefore the rate of reaction will decrease. I predict that rennin will still work in neutral conditions because milk is neutral and therefore rennin cannot be denatured by neutral conditions.

Also the hydrochloric acid in the stomach is diluted by the other gastric juices, food and milk, so the rennin must be able to work in weak acids. However in extreme alkali conditions I predict the rate of reaction to be zero because varying the pH can change the bonds within the enzyme, and therefore change the shape of the active site until the substrate is unable to fit into it - ie it is denatured. 11. Concentration of Enzyme How will the concentration of the rennin affect the rate of reaction? I know enzymes function efficiently in low concentrations as the molecules can be used over and over again. However, I predict that an increase in the concentration of rennin will lead to a corresponding increase in the rate of reaction up to a point. For when there is enough enzyme to hold every molecule of substrate, an increase in enzyme concentration will have no effect.

The graph shows how the rate of reaction will be directly proportional to concentration up to the limiting point. 12. Which Variable has the Greatest Relative Effect? I think that temperature will have the greatest effect on the rate of reaction. For I have predicted that relatively small changes in temperature produce a large change in the rate of reaction of rennin. For without enough energy provided by heat rennin cannot have as many successful collisions with caseinogen, and the reaction is very much hindered.

Temperature also can completely stop the rennin by denaturation. The other two variables, I predict, will have a less overall effect on the reaction. For I know enzymes work very economically in small concentrations because they can be used over again, and therefore variation in concentration will have no dramatic effect on the rate of reaction. I know that rennin works best at pH 1, however, I predict that it will continue to break down caseinogen in pH higher than this because in the stomach of a mammal, where rennin is found, the hydrochloric acid is diluted by the other liquids in the stomach and the food or milk that the animal has eaten. Therefore, rennin must be able to work in acid much weaker than pH 1 which suggests that pH will have less overall effect. PLANNING To get successful and accurate results I am going to test each of the variables (temperature, pH, and concentration) separately whilst ensuring that the remaining two remain constant. 13.

Measuring the Rate of Reaction Rennin, I know, catalyses the conversion of the protein of milk, caseinogen, into paracasein, which precipitates as a calcium salt. Therefore by timing how long it takes this to occur, ie for milk to clot, I will be able to get an indication of the differing rates of reaction. To ensure a fair test, I am going to stop the stop-clock when the milk has fully clotted and the whey is fully separated from the curd. The faster it takes to clot, the faster the rate of reaction. 14.

Quantities For each experiment, so that I can compare them in my conclusion, I am going to use 2 ml of milk and 4 drops of rennin (obviously for the concentration experiment, this will vary). To ensure a fair test each experiment will be conducted with the same type of milk - semi-skimmed. 15. Plan for Temperature To study how temperature affects the reaction between milk and rennin, I am going to look at a range of different temperatures between 0 C and 80 C. I chose a minimum temperature of 0 C because it is the coldest temperature I can achieve with the apparatus available to me. I chose a maximum temperature of 80 C because at this temperature I would expect, after my research and prediction, for all the rennin to be denatured. Also 80 C is still a safe temperature to work at, and the milk won't curdle too quickly.

I am going to use temperatures at 20 C intervals within the 0 C to 80 C guidelines so that I am able to get detailed results whilst ensuring that there is a significant difference in the rate of reaction. To keep all other variables the same I am going to use the same amount of milk (2 ml) each time and use the maximum concentration of rennin. I know milk to be of neutral pH after testing it with universal indicator paper and have decided to leave it so. For, though I know rennin to react best in acidic conditions, by adding hydrochloric acid to provide favourable conditions, I would be unsure whether it was the acid or the temperature having the most effect on the reaction, and I would have inaccurate results.

Also, hydrochloric acid separates milk itself, so the reaction would begin before the rennin was added. When heating or cooling, I will do exactly the same to both the milk and the rennin, to ensure that both are at the same temperature and it is not just the milk being heated while the rennin remains at room temperature, which would, of course, effect the results I received. For if the milk was at 80 C, but I had not heated the rennin, the enzyme would still be able to react with the milk until eventually the rennin itself had reached a high temperature and was denatured. To ensure that the enzyme and substrate remain at the required temperature I am going to pour them together and watch for the reaction whilst they are still in their set conditions, ie I will not take the boiling tube out of the water bath.

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Research essay sample on Rate Of Reaction Hydrogen Bonding