• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month
Page
  1. 1
    1
  2. 2
    2
  3. 3
    3
  4. 4
    4
  5. 5
    5
  6. 6
    6
  7. 7
    7
  8. 8
    8
  9. 9
    9
  10. 10
    10
  11. 11
    11

Starch and diastase with respect to pH

Extracts from this document...

Introduction

Starch and diastase with respect to pH Aim The aim of this experiment is to assess the effect of pH on enzyme activity. To do this I will use diastase as the enzyme and starch as the substrate, I will then vary the pH and measure the effects. Hypothesis There will be an optimum pH, between pH 4 and pH5, at which diastase will hydrolyse starch. Background information Enzymes are globular protein molecules that are biological catalysts, so they reduce the energy needed for the reaction but don't get used up themselves. Being a globular protein, enzymes are formed from a tertiary structure, so they are 3-D molecules. As a result they are able to have an active site, this is where the substrate binds to the enzyme and is broken down into the products. An active site consists of 3-12 amino acids and it is thought that the active sites have specific shapes that correspond to specific substrates. Consequently the enzyme can only break down that particular substrate molecule, this is known as the lock and key theory. However recent research has shown that the enzymes active site is not the right shape to start with, but once it combines with the substrate molecule a small change occurs in the shape of the active site. Subsequently the substrate fits better in the active site, this is known as the induced fit hypothesis. An enzyme can be affected by different factors. They can be denatured by high temperatures because the particles within the enzymes receive energy as the temperature rises, so a large rise in temperatures results in the molecules vibrating a lot. This disrupts the weak hydrogen bonds holding these particles together the ionic bonds are also broken and so the enzymes active site collapses, this means that the enzyme can no longer break down the substrates as the substrate won't fit in the active site anymore consequently the rate of reaction is decreased. ...read more.

Middle

* Substrate concentration - we will make sure that we use the same amount of starch each time and use the same measuring cylinder * Enzyme concentration - we will make sure we use the same amount of diastase for each experiment and we will use the same syringe * Time - we will begin timing as soon as all the diastase has gone into the cuvette and as soon as the 4 minutes is up we will add the iodine and put it straight into the colorimeter. * Apparatus - we will use the same apparatus for each thing, e.g. we will use the same syringe for pH and a different one for diastase. Also when changing pH, the syringe will be washed out. * Once every thing is in the cuvette we will give a quick shake and then leave it in a test tube holder. Preliminary We conducted a preliminary following the method above, but not using any pH buffers so it was a control. We also conducted another where we added the iodine from the beginning and put it straight into the colorimeter, and at the end of each minute for 4 minutes we recorded the results. Preliminary results Experiment Transmission (%) Control 72% pH 1 minute 2 minutes 3 minutes 4 minutes 4 33% transmission 40% transmission 42% transmission 41% transmission We can establish from these results that the control worked well. However when we took the test tube out of the colorimeter on the second experiment we noticed that the iodine hadn't mixed well with the other solutions so we decided to keep the method the same. Results Temperature = 20�C Red = anomalies Transmission at different pHs Experiment no. pH 4 pH 5 pH 6 pH 7 pH 8 pH 9 1 80% 93% 93% 90% 90% 78% 2 82% 90% 90% 92% 75% 52% 3 83% 82% 94% 87% 84% 46% 4 80% 94% 93% 79% 40% 5 82% 89% 78% 6 89% 92% 7 89% Average (excluding anomalies) ...read more.

Conclusion

Also when we first added the iodine it went black but it soon began to clear and by the time we had taken the reading it was very clear. However we couldn't keep the solution in the colorimeter and then add the iodine straight after the four minutes, as the light that needed to pass through the solution was quite near the bottom and you needed to swirl the solution after adding the iodine so it would mix. To get better results we would need more time to get more results so they become concordant and we would be able to get a better understanding of what was happening when you varied the pH. If it were possible, some sort of solution that could stop the reaction would be useful so that when we added the iodine the reaction wouldn't keep on going. Also I would imagine that by using smaller amounts of each solution would mean that we would be able to add the iodine to the cuvette when it was in the colorimeter as the solution would need to be mixed, so we would get more accurate results. In addition, if we added more iodine we would be able to ensure more of it was mixing and quicker. Additionally we could use new syringes every time we changed pH buffer solution, this would ensure accuracy. Furthermore we could begin timing as soon as the measuring cylinder is overturned, so that by the time the solution has mixed, the timer would have started. Generally we would have to be extremely careful when using the colorimeter, to ensure the table wasn't knocked. We would also have to place the cuvette in the colorimeter very carefully. Despite the fact that there were many opportunities for the results to become unreliable and inaccurate, the results that the experiment did yield followed a general trend and followed what was expected when the pH of the solution was altered. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our AS and A Level Molecules & Cells section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Molecules & Cells essays

  1. Marked by a teacher

    How does the concentration of enzymes affect the breakdown of starch by a-amylase in ...

    4 star(s)

    Wait until the iodine solution has reacted with the starch. In the presence of starch, iodine solution turns blue/black. However, if no starch is present, the iodine solution takes on a different colour. This means that around the well, where the enzyme has broken down the starch, there will be

  2. Marked by a teacher

    How does the pH affect the activity of amylase

    3 star(s)

    When we look at the graph showing the rate we get a similar view Biological explanation To explain this first it is good to go back to the basics and understand how the enzyme works. Amylase is a protein, and its function is determined by its complex structure in it

  1. Marked by a teacher

    How Does the pH of a Solution Affect the Rate of Starch Digestion By ...

    3 star(s)

    The time scale was too wide for me to make any clear conclusions about the effectiveness of the pH difference on the enzyme's effectiveness. What is Starch? Starch is a complex carbohydrate which is made up of a combination of two different types of polysaccharides, they are amylase and amylopectin.

  2. Experiment to Investigate the Effect of Copper Ions on a Solution of Amylase and ...

    Bacterial amylase was used therefore there were no possible sources of objections. Variables It is important to ensure that the variable being tested (dependant variable) in this experiment is not affected by other independent variables such as the following. These variables must therefore be kept constant throughout the entire experiment.

  1. What effect does the pH have on the enzyme diastase? What effect does the ...

    Table One shows that the darkest colors have been obtained at temperatures of 10oC, 20oC and 70oC. As it follows, the first two temperatures show that they are too low for the enzyme to function in. The following tests were done every minute, until no further change was noticed.

  2. 'Investigating how temperature affects the rate action of the amylase enzyme on starch.'

    Testing requires the procedure "DIP-TEST-RINSE-WIPE" i.e. using a glass rod to dip into the test tube then touch the iodine on the spotting tiles. Finally rinse in some water and wipe with a paper towel. * 10.) Repeat step 9 every 15 seconds until the colour of the iodine in the hollow does NOT change colour.

  1. How does pH affect the Denaturation of enzymes Starch and Amylase.

    I tried another experiment with just pH 12, and added drops of iodine to it. The pH turned colourless straight away, showing that it was the high pH 12 that was making the iodine colourless, and no other factor. To query about the other levels of pH, I set-up tubes

  2. An Experiment to investigate the affect different temperatures have on the rate of an ...

    Hence the use of the colorimeter. Each curette is placed into the colorimeter and the percentage of light transmission through the solution is recorded. Initially a sample of pure iodine would need to be tested and made to give the result of 100% transmission. The way that the colorimeter works is by shining a light through

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work