Investigate the factors affecting the rate of breakdown of sucrose by the enzyme sucrase (invertase).

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GCSE Biology Coursework

Investigate the factors affecting the rate of breakdown of sucrose by the enzyme sucrase (invertase)

Avninder Gidar

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Definition of enzyme

An enzyme is a biochemical catalyst that enormously accelerates a chemical reaction. Enzymes are complex protein molecules highly specific to particular reactions. (Taken from the Collins Dictionary of Medicine)

How enzymes work

Enzymes have an area - usually thought of as a pocket-shaped gap in the molecule - which is called the active site. 

The substrate (or substrates) fits/fit into the active site, but enzymes are specific so only a certain substrate will fit a particular enzymes active site. There are several types of enzyme which contribute to different types of biochemical reaction.

The enzyme speeds up the process of conversion of substrates into products.
Although the enzyme joins with the substrate for a short while, the enzyme and substrate split apart afterwards, releasing the enzyme. Thus the enzyme is not used up in the process unlike the substrate, so it can continue to react if more substrate is provided.

The enzyme I am investigating and what it does

I am investigating the rate at which the enzyme sucrase breaks down its substrate sucrose.

Sucrose is a type of sugar used by many plants as a convenient form in which to move carbohydrate around the plant i.e. from leaves to roots.

Each sucrose molecule consists of two single glucose molecules joined together and the sucrose must be broken down before it can be used to provide energy through respiration.

The enzyme sucrase is used to break down the sucrose molecules into glucose so they can be respired.

Factors that effect the rate at which enzymes breakdown

There are many factors that affect the rate at which enzymes breakdown their substrate for example –

  • Temperature

  • pH

  • Concentration of Enzyme

  • Concentration of substrate

  • Volume of Enzyme

  • Volume of Substrate

  • Time

  • Rate of stirring

Time

Time does not frankly affect the rate as in this reaction the rate is directly proportional to time.

But time does play a role at the beginning of the experiment just as the enzyme is added to the substrate it takes a small amount of time for the breakdown to begin.

This time varies from factor to factor for example, for a factor that increases the rate at which enzymes react this time will be very small, but for a factor that slows down the rate at which enzymes reacts this time may be slightly longer.

Concentration of Enzyme

The concentration of enzyme affects the rate in 1 main way (concentration of substrate kept the same).

The higher the concentration of sucrase the faster the rate it breaks down is.

This is because there will be more enzymes to react with the sucrose, so there will be more collisions per unit time and all the sucrose will be broken-down faster.

I believe that the concentration of enzyme is directly proportional to the rate, but this is just a prediction. This could be a factor to investigate.

Concentration of Substrate

Increasing the concentration of sucrose will affect the rate the opposite way the concentration of sucrase will. (Keeping the concentration of sucrase the same)

This is because in higher concentrations of sucrose there will be more sucrose to be broken down with the same amount of enzymes so it will take longer for the total breakdown thus the rate is slower.

I believe that the concentration of substrate is inversely proportional to the rate, but this is just a prediction. This could be a factor to investigate.

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Volume of enzyme

(Keeping the volume of sucrose and concentration of both the same) Increasing the volume of sucrase will increase the rate as there will be more enzymes therefore more enzymes will react per unit time and the rate will be faster. I believe that the volume of enzyme is directly proportional to the rate, but this is just a prediction. This could be a factor to investigate.

Volume of substrate

(Keeping the volume of sucrase the same and the concentration of both solutions the same). Increasing the volume of sucrose will decrease the rate ...

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