Investigating Factors That Affect The Action of Pepsin on Photographic Film

Investigating Factors That Affect The Action of Pepsin on Photographic Film

Introduction

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This is an experiment to investigate the factors that affect the

action of pepsin on photographic film. The photographic film is made

up of three layers, plastic, photographic pigment and gelatine in

between. See diagram:

The protease enzyme digests the gelatine section, causing the other

two layers to fall apart.

Pepsin is a digestive enzyme found in the gastric juice of the

stomach. It changes proteins in food into substances called peptides.

In chemical composition, pepsin is like other enzymes, but its effects

are entirely different. Its activity is strongest in an acidic

environment, such as that found in the stomach. Pepsin has no effect

on fats or carbohydrates. It is produced commercially by drying the

mucous lining of the stomachs of pigs and calves.

The variables for this practical are:

Temperature - Increasing the temperature give the molecules more

energy.

Concentration of enzymes - The more enzyme there is, the more

molecules there are working.

PH - Different enzymes work best at different levels of pH.

Concentration of substrate

I have chosen to investigate temperature. I predict that raising the

temperature will raise the rate of reaction until it reaches its

optimum temperature. Raising the temperature beyond this point will

lower the rate of reaction until it is too high for a reaction to take

place.

Here is a graph of rate and temperature:

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Activation energy

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For a reaction to take place the molecule must have sufficient kinetic

energy, known as the activation energy. At the higher temperature,

more molecules are past the activation energy line, so when there is a

collision it is more likely to create a reaction.

Varying the temperature will change the rate of reaction due to how

much energy the molecules have. When there is a higher temperature the

molecules have more energy, so they move around faster.