To investigate the effect of cellulase on fruit juice extaction.

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Pamela Jones 09/05/07

AS LEVEL BIOLOGY COURSEWORK

TO INVESTIGATE THE EFFECT OF CELLULASE ON

FRUIT JUICE EXTRACTION

  1. METHOD An amendment was made to the suggested method for practical reasons.  Instead of leaving the apple puree in the enzyme solution for twenty four hours at room temperature, beakers containing the samples were immersed for one and a half hours at 40oC in a thermostatically controlled water bath.  

  2. RESULTS

Table of  Results
 See over for table prepared for results and observations and completed during the experiment.  Since the 0% enzyme immersion solution would not be expected to change fruit juice extraction, this datum was used as a control and fruit juice volume produced calculated by subtracting this baseline volume from the total observed at each enzyme concentration (see table below).  The percentage of cellulase is the independent variable and the increased or decreased volume of juice produced is the dependent variable.


  1. GRAPH (see graph paper over)

    A hypothesis for this experiment would predict a significant increase in fruit juice extraction using cellulase.  Since the hypothesis predicts a change in the dependent variable as the independent variable changes, the appropriate graphical treatment of the data was to use a scatter graph.  Since no assumptions can be made about data between those observed, datum points have been joined by straight lines.

  2. INTERPRETATION OF RESULTS

    Since the original volume of enzyme solution was 10 cm3 , the additional volume of fruit juice produced without enzyme was insignificant (+ 0.3 cm3) confirming the use of the 0% datum as a baseline.  The graph shows a net increase in apple juice extraction using the enzyme solutions at 0.5%, 1.0% and 2.0% compared with 0% cellulase.  Using the 1.5% solution there was actually an observed but minute and insignificant net decrease in juice extraction.  This was almost certainly an anomalous result (see evaluation section below).  Leaving aside the 1.5% result, therefore, the graph shows an initially higher effect (change in production of fruit juice) followed by a lower effect which may be tending to zero (graph tending to a plateau).  There are too few data points to be certain of the latter, however.  (See evaluation.)  

    An enzyme catalyses a biological reaction by reducing its activation energy.  Most chemical reaction rates increase with increasing temperature because of an increase in kinetic energy of the substrate(s).  Increased kinetic energy increases the likelihood of substrates having the necessary energy to reach the transition state of a reaction by decreasing the time to achieve equilibrium.  Biological reactions cannot use increased temperature in order to increase reaction rate because they exist within a narrow temperature range.  Enzymes catalyse biological reactions by providing an alternative pathway from product to substrate which has a lower activation energy.














    According to Daniel E. Koshland’s Induced Fit Theory of enzyme action (1958), substrates bind to an active site on the enzyme and by so doing cause a conformational change in the enzyme which in turn improves the enzyme-substrate complex binding fit.  The substrate is distorted so as to lower transition state energy and to position amino acid side chains in exactly the right place to aid the catalytic process.  The reaction is visualised as occurring in two distinct steps, the second being effectively irreversible (Michaelis-Menten model, 1913)

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E + S                 ES                where E = Enzyme, S = Substrate(s)

                                        ES = Enzyme/substrate complex and P = Product(s)

ES                E + P

The enzyme is unchanged by the reaction.

Cellulase catalyses the breakdown of cellulose to β-glucose sub-units (or sugar acids)

                                           
cellulase
                       
                       Cellulose                   β-glucose


Plant cells have cell walls ...

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