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Proteins are organic compounds of large molecular mass. They are not truly soluble in water; instead they form colloidal suspensions. Proteins are made up of amino acids..

There are three main types of bonding. The first is a disulphide bond. This occurs between cysteine molecules in the same amino acid chain (intrachain) or between molecules in different chains (interchain). This is the strongest and last bond to break.

The second bond is an ionic bond. At a suitable pH, an interaction may occur between ionised amino and carboxylic groups. This forms an ionic bond. These ionic bonds are weak and can be broken in an aqueous solution by changing the pH of the medium surrounding the polypeptide.

The third bond is the hydrogen bond, which occurs between hydrogen and oxygen atoms within the polypeptide chain. Hydrogen bonds are not strong on their own, although a large number of them together makes them very strong.

The primary structure is the linear sequence of amino acids stablised by peptide bonds. There are an endless number of different possible primary structure

The secondary structure is the sequence of amino acids arranged as either an alpha helix of a beta pleated sheet stabilised by peptide s. bonds and hydrogen bonds. In an alpha-helix the structure is mainly stablised by hydrogen bonds, which are formed between adjacent CO and NH groups. Tertiary structure is the way in which proteins form to make a three dimensional structure. Polypeptide chains bend and fold to form a globular shape.

The quaternary group is the association of different polypeptide chains.

The polypeptide chains are held together by hydrophobic interactions, hydrogen bonds and ionic bonds. The arrangement of these bonds is the quaternary structure.

When protein is denatured the specific shape formed by the four types of structures is broken down. Denaturation is a physical change in the shape of the protein molecule. This is due to the bonds, which normally hold the proteins specific three dimensional shape, being broken

Aim of the Experiment

To discover the lowest concentration of copper sulphate solution that will denature egg albumen.

Prediction

The copper sulphate ions will break down the tertiary structure causing the protein to denature. This will cause the egg albumen to turn white and opaque. The higher the concentration of the copper sulphate the faster and more opaque the albumen will turn, this is due to the increase in number of copper ions present in the solution.

Apparatus

5 Test tubes

Test tube holder

Egg Albumen from a fresh egg

0.1Molar Copper Sulphate solution

5 Petri dishes

Marker Pen

5ml Syringe

Distilled Water

Diagram of apparatus set up

Safety

Copper sulphate is harmful when swallowed and it is also an irritant to the eyes and skin, for this reason care was taken when handling to copper sulphate

Method

Five different concentrations of copper sulphate solution were made up, at concentrations 0.02M, 0.04M, 0.06M, 0.08M and 0.10Molar. To make the concentrations 0.1molar copper sulphate was used. To make concentration of 0.08M copper sulphate 8cm3 of copper sulphate was measured into a test tube and then it was filled to 10cm3 with distilled water. This method was repeated for the other concentrations. Five petri dishes were set up and 5ml of egg albumen were placed in each. Three drops of 0.1M copper sulphate solution was placed into one of the petri dishes containing egg albumen. This method was repeated for the rest of the concentrations. To prove that the copper sulphate is the cause of the denaturation of the protein in the egg white distilled water was used. This contains nothing other than pure water and no reaction will occur. This is called the control and all the results can be compared to it to determine whether a reaction has occurred.

The fixed variables of this investigation are volumes of egg albumen used and the volume of copper sulphate solution. The independent variable is the concentration of copper sulphate. The dependant variable is whether the egg albumen has denatured or not.

To ensure fair testing throughout the investigation the egg albumen used was from the same egg. The same volumes were used and measured using a syringe rather than a measuring cylinder, to ensure accuracy.

The results obtained are qualitative, as there is nothing that can easily be measured. One way of obtaining quantitative results is to centrifuge the solutions after denaturation has occurred and this will show how much of the albumen has been denatured.

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