A photographic company wants to recycle the plastic in exposed (and therefore unusable) photographic film. They will need to remove the silver compound attached to the film by the protein gelatine. They decide to use a protease enzyme called trypsin

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Introduction

A photographic company wants to recycle the plastic in exposed (and therefore unusable) photographic film. They will need to remove the silver compound attached to the film by the protein gelatine. They decide to use a protease enzyme called trypsin to digest the gelatine, but want to find the best conditions for the enzyme to work to save money.

Background knowledge

ENZYMES

An enzyme is a biological catalyst that speeds up the rate of reaction. Enzymes are composed of polymers of amino acids. Enzymes are mainly located in the cytoplasm of a cell. Here they control the chemical reactions occurring inside the cells. The enzymes break down the food molecules into smaller parts so it is much easier for it to pass through the blood stream. Many enzymes are produced in different parts of the digestive system. The digestive system produces enzymes that break down the components of the food we eat.

They speed up reactions by a process called the induced fit theory. It was first thought that the 'lock and key' hypothesis was how the enzymes work, but this is now believed to be incorrect because the enzymes can change shape so that the substrate (the thing that is broken up) can fit into the active site of the enzyme, which is why it is called the induced fit theory. The lock and key theory suggests that the enzymes are the correct shape without having to change for the substrate to fit in, which they often are not. The substrate enters the enzyme and is digested in the active site of the enzyme.

WHAT IS TRYPSIN?

Trypsin is an enzyme that acts to degrade protein; it is often referred to as a proteolytic enzyme, or proteinase. Trypsin is one of the three principal digestive proteinases, the other two being pepsin and chymotrypsin. In the digestive process, trypsin acts with the other proteinases to break down dietary protein molecules to their component peptides and amino acids. Trypsin continues the process of digestion (begun in the stomach) in the small intestine where a slightly alkaline environment (about pH 8) promotes its maximal enzymatic activity. Trypsin, produced in an inactive form by the pancreas, is verysimilar in chemical composition and in structure to the other chief pancreatic proteinase, chymotrypsin. Both enzymes also appear to have similar mechanisms of action; residues of histidine and serine are found in the active sites of both. The chief difference between the two molecules seems to be in their specificity, that is, each is active only against the peptide bonds in protein molecules that have carboxyl groups donated by certain amino acids. For trypsin these amino acids are arginine and lysine, for chymotrypsin they are tyrosine, phenylalanine, tryptophan, methionine, and leucine. Trypsin is the most discriminating of all the proteolytic enzymes in terms of the restricted number of chemical bonds that it will attack. Good use of this fact has been made by chemists interested in the determination of the amino acid sequence of proteins; trypsin is widely employed as a reagent for the orderly and unambiguous cleavage of such molecules.

Below is the word equation for the process of recycling exposed photographic film with the enzyme, trypsin: -

Below is a diagram of the lock and key theory

Above is a diagram of the induced fit theory.

Aims of my investigation

In the investigation I am going to study one of the four factors that alter the rate of reaction of trypsin in the clearing of photographic film. In photographic film is the clear acetate at the bottom and on top of that is geletin (a substrate) which has silver salts in it. When trypsin is added, the gelatin is broken down and the acetate becomes clear. The reaction can occur at different speeds depending upon the factors acting on the trypsin. These factors are the pH of the environment, the temperature, the concentration and inhibitors. The factor that I will be controlling in this experiment is temperature.
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Prediction

The factors that will affect the rate of reaction of Trypsin are....

pH

This can alter the rate of reaction because if the pH is too high or too low for the enzyme, it will become denatured, where the structure of the enzyme is changed so that substrates will no longer be able to fit inside the enzyme and therefore will not be digested. Most enzymes work best at pH 7, although some enzymes in the stomach work best in very acidic conditions (pH 1 or 2). The enzyme in my investigation (trypsin) works ...

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