CP12 Write up - Effect of temperature on the initial rate of an enzyme-catalysed reaction, to include Q10
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Course
Core Practicals
Institution
PEARSON (PEARSON)
Edexcel A Biology A level core practical Write ups. All include an introduction, hypothesis, variables, method, results, evaluations...
CP12 - Investigate the effect of temperature on the initial rate of an enzyme-catalysed reaction, to include Q10
Investigate the effect of temperature on the rate of an enzyme-catalysed reaction, to include
Q10
Aim: To investigate the effect of temperature on the initial rate of reaction of an enzyme-
controlled reaction.
Introduction
Hydrogen peroxide is generated in numerous biological processes and is implicated as the
main transmitter of redox signals. Although a strong oxidant, high activation energy barriers
make it unreactive with most biological molecules. The most favoured reactions of hydrogen
peroxide are with transition metal centres, selenoproteins, and selected thiol proteins such
as catalase (Winterbourn, 2013).
Catalase is a common antioxidant enzyme with the highest turnover rate. It is present in
living tissues and is a key clinical enzyme involved in the breakdown of hydrogen peroxide to
water and molecular oxygen. It is found in erythrocytes and its exogenous sources are from
plants including various fruits and vegetables such as peas.(Sharma and Ahmad, 2014).
When catalase is added to hydrogen peroxide, there is an initial rapid evolution of oxygen
which lasts for about two minutes, depending on the peroxide concentration. After this,
oxygen is given off at a steady rate which slowly decreases in the course of an hour. This
decrease in the rate is undoubtedly due to enzyme destruction, and several kinetic equations
have been developed to account for it. The rapid evolution and the steady rate, however, are
inherent features of the peroxide decomposition (George, 1947).
Enzymes are globular proteins, acting alone or in larger complexes. Like all proteins,
enzymes are linear chains of amino acids that fold to produce a three-dimensional structure.
The sequence of the amino acids specifies the structure which in turn determines the
catalytic activity of the enzyme. Increasing the temperature increases the rate of reaction up
to an optimal temperature however then causes it to denature thus freewing the reaction
rate. Enzyme structures unfold (denature) when heated or exposed to chemical denaturants
and this disruption to the structure typically causes a loss of activity (Chemistry LibreTexts,
2016).
Hypothesis :
For each temperature, there will be an initial rapid evolution of oxygen which will slow to a
steady rate.
Increasing the temperature will increase the rate of oxygen production up to a certain
temperature. After that optimum temperature, the rate of oxygen production will decrease as
enzymes denature
Variables
Independent variable : Temperature of water bath (20°C-60°C going up in 10°C) in which
the boiling tubes are placed and thus the temperature at which the hydrogen peroxide and
peas are reacting at.
Dependent variable : The volume of oxygen gas (cm3) produced and measured using a gas
syringe in a given amount of time
, Core Practical 12 -10/08/2022
Control variables :
- Concentration and volume of pea solution - the same number of peas (10) should be
crushed
- Concentration and volume of hydrogen peroxide - measure 5cm3 of the same
concentration using a measuring cylinder
- Time of acclimatisation - let each test tubes sit in the water baths for 2 minutes
before starting the reaction
Risk assessment
Hazard and risk Safety measure
Hydrogen peroxide is an irritant (Low risk) Wear eye protection and wear gloves to
prevent skin contamination. Do not handle
directly, use a spatula. Wash hands after
use. Do not ingest
Glasswares such as test tubes are fragile Take care when handling glassware and
causing them to break easily. They have keep away from the edge of surfaces.
very sharp edges when they’re broken, this
may cause skin injury (Low risk)
Hot liquids from water bath can cause Handle with care when using the water bath
scalding and use tongs to remove test tubes
Equipment
● Soaked peas - softens the peas, making
● Hydrogen peroxide solution - substrate for the catalase to react with
● Distilled water - control
● Stop clocks - to track how much gas was produced
● Delivery tubes with bungs to fit the boiling tube - to collect the gas produced into
the syringe
● Forceps - to take out the boiling tube out of the hot water baths
● Electric water baths at a range of temperature - to control the temperature at
which the reaction occurs (independent variable)
● Boiling tubes - for the reaction to occur in
● Measuring cylinders - to accurately measure the volume of pea solution and
hydrogen peroxide
● Pestle and mortar - to grind the peas and make a solution
● Clamp stand and clamp - to hold the apparatus
● Gas syringe - measure the volume of gas produced
Method
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