Secondary protein structures are polypeptides that become twisted or coiled. These are held by hydrogen bonds
Tertiary proteins are where polypeptides are folded into precise shapes. It is held in a permanent shape by bonds such as hydrogen and ionic bonds and this is a 3D shape.
Quaternary proteins consist of different polypeptides bonding together to form extremely intricate shapes. An e.g. is haemoglobin.
Preliminary Experiment
I started my experiment by using 5ml of egg albumen and 1ml of copper sulphate. The problem faced was that the results where not consistent. I concluded that it was down to the huge difference in range in the amounts used. So I then decided to use 2ml of egg albumen and 1ml of copper (II) sulphate. After then repeating the experiment at these amounts I then was able to get some consistent results. Also I decided that the experiment would be done over 1min so giving time for the reaction to occur. There was still another problem to be looked at, that is to consider weather the albumen is to be stirred once the copper (II) sulphate was put in. From doing the experiment it could be seen that when not stirred the copper (II) sulphate put in would stay at the top of the test tube so it was necessary to stir to mix the albumen and copper (II) sulphate together so we could get a result that the colorimeter could read. Another problem, was that the egg albumen when a high concentration of copper (II) sulphate was added, it went very viscose.
The main problem was getting the precise amount of egg albumen, because it was so thick that the syringe found it hard to take up. Also I stirred both mixtures before using them so they stayed in suspension.
Prediction
I predicted that as the concentration of copper (II) sulphate was decreased the amount transmission (%) would increase in the colorimeter. I predicted this would happen, because as the concentration decreases of the copper (II) sulphate then the rate of reaction will decrease and so the peptide bond which, were broken by the copper (II) sulphate at a higher concentration will not be broken because they will resist and the reduced copper (II) sulphate concentration will mean less distorted shape and charge of the molecule. Also from my preliminary work, I found that when the molar was decreased to 0.04molar I then got an increase in the transmission percentage.
Percentage
transmission
Concentration
Experimental Plan:
After the preliminary experiment, I concluded that the best amounts were 2ml of egg albumen and 1ml of copper (II) sulphate. To make the experiment more accurate I shall do a repeat to get reliable results and I will then take an average to get reliable and accurate results and the measurements for the percentage of transmission will be to 2-sig fig and the concentration will be to 2 decimal places. The amounts of the egg albumen and copper (II) sulphate will be fixed and the only variable used will be the changing of the concentration of copper (II) sulphate. The degree of accuracy for the substance collected was 1 sig fig for the egg and copper (II) sulphate.
Method:
First I collected all the apparatus as stated below. Next I stirred the solutions before using them so they were in suspension. I then proceeded in collecting 1ml of copper (II) sulphate and put it in the test tube. For this I used a 2ml syringe. Next for the egg albumen I used a different syringe so not to contaminate the two solutions. Once the 2ml of egg albumen was added I started the timer for 1min and whilst doing this I stirred the mixture with a stirring rod for a minute. Once the 1min was up I used the colorimeter and found the amount of transmission in %. Then the experiment was done the same for each concentration, but the only difference was the amounts for the copper (II) sulphate. This is shown below.
Calculating Concentration
Apparatus:
14 test tubes
20cm of copper (II) sulphate (1ml used for each experiment)
50cm of egg albumen (2ml used for each experiment)
100cm distilled water
Colorimeter
Test tube rack
2x 20cm beckers
1x 250cm beaker
Glass marking pencil
Stop Watch
Glass stirring rod
2x Syringe 2ml
Thermometer
Percentage
Transmission (%)
Concentration of copper (II) sulphate (moles)
Graph
From this graph we can see that all the way to the concentration of 0.05 there is still full denaturation, but at 0.04 the amount absorbed it now 3%. This shows that the lowest concentration that brings around full denaturation of egg albumen is between 0.05 and 0.04. Also the graph shows that passed 0.04 the amount of transmission % increases until we get to 0 where the transmission % is 100.
How did I make it a Fair Test?
The variables that I had to deal with were temperature and pH and egg albumen.
First I had to deal with the temperature. The temperature of the room stayed the same, so this meant that it was controlled at 21°C. If the temperature was changing then I could have used a water bath at 21°C.
Secondly, I would control pH by using a buffer to stop the pH from changing if a pH change was noticed.
Thirdly, I used the same egg albumen all the way through because if I had changed it and had a different batch it may have caused anomalous results. Also I stirred the albumen before using it so it was in suspension.
Fourthly, I did vary the concentration and I did 7 different concentrations to determine where the lowest concentration was where denaturation happened fully. I also did a control with a concentration of 0 to see if with no copper (II) sulphate there would be denaturation.