How will temperature affect the rate at which rennin acts on milk?

Benjamin Powell 11KR Triple Science Coursework

Introduction.

The Kinetic Theory states that with increased temperature, molecules receive more energy, resulting in them speeding up their movement. If the starch and the catalase 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.

Preliminary Work.
Enzymes are large globular molecules of which the vast majority is protein in nature. 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 act as catalysts, reducing the need for activation energy and so allows reactions to take place more readily and at lower temperatures than would otherwise be necessary. This can be seen in the graphs.

Prediction.

I predict that the catylase will take less time to react with the starch as the temperature increases. However, above 40°C, I predict that the rate of reaction will decrease. This is because the rising temperature affects the hydrogen and ionic bonds that 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 catalase 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.

The reaction of catalase with starch can be shown in graph form.

Explanation of graph

A is to do with collision theory; the ions need a lot of time to ...

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The reaction of catalase with starch can be shown in graph form.

Explanation of graph

A is to do with collision theory; the ions need a lot of time to collide successfully.

B is the optimum temperature; less time is needed to make the reaction take place.

C is when the enzymes have denatured; they no longer fit together.

Variable

My variable is going to be the temperature because that will have the greatest effect on the rate of reaction. Small changes in temperature produce large changes in the rate of reaction of catalase, in fact after each 10°C temperature increase the rate of reaction doubles. Without the energy produced by heating up the starch, it cannot have as many successful collisions with caseinogen, and the reaction is delayed.

Range

The range will be from 00C to 600C. I chose a minimum temperature of 00C because it is the lowest possible temperature achieved with the apparatus available. I chose a maximum temperature of 600C because at this temperature I would expect after research and prediction that the majority of the rennin will have denatured. Also 600C is a safe temperature to work at. It will go up in 20C each time. The change in how much the temperature goes up by is 20C. Because cows' body temperatures are roughly 38.60C, by going up in twos it is close as possible to the enzymes optimum working temperature.

Fair testing

To keep this experiment fair I will need to have a control and things that are going to remain constant. My constants are time, the concentration of , pH and the type of milk, semi-skimmed. The drops of rennin will be 10 because I found that in my preliminary results it gave me the best range of results. I know that milk is a neutral pH after researching it on the Internet and testing it for myself and I will leave it as it is. Although rennin reacts best in acidic conditions by adding Hydrochloric Acid (HCl) it separates milk itself so the reaction would start before the rennin was added. Also I would be unsure whether it was the acid or the temperature having the most effect on the reaction; this would give me inaccurate results.

Method

Collect equipment: thermometer, potato, scalpel, tile, Bunsen burner, measuring cylinder, 500ml beaker and a test tube
.
ecord results.
Repeat all of the above, changing the temperature by 20C each time

Analysis

At point A in the graph it is taking a long time for the rennin to react with milk. At point B the rennin is at its optimum working conditions. At point C it takes longer for the rennin to react with the milk. It takes longer for the rennin to react with the milk because the enzyme and substrate molecules aren't receiving much energy and the movement will slow down, this reduces the number of collisions between the rennin and the caseinogen and it is highly unlikely that the collisions will be successful. It took a long time for the rennin to react (point C) because the enzymes are denaturing. The high temperature is causing the enzymes to change shape, which means that the substrate molecule will not fit in the active site, therefore not helping the reaction. As with many experiments there were some unexpected results at 440C the enzyme took less time to react. This could be because I added too many drops of rennin or the temperature didn't remain stable.

Evaluation

My experiment was done well but it did produce an anomalous result. At 440C the result did not follow the pattern. It took the least amount of time to react with the rennin this is because I added more drops of rennin. To get more accurate I could do one of many things. I could change what I used to measure the rennin; I could use a measuring cylinder instead of a pipette because that would produce a smaller margin of error. To improve my experiment I could also change the method. For example when heating the rennin in the water bath, using a Bunsen to heat it isn't reliable because you can't keep the temperature constant. Alternatively I could have used a proper water bath to keep the rennin at a constant temperature. If I were to extend this investigation I could investigate the effects rennin has on goat's milk and compare it to cows milk.