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Enzyme Action
Intermediate 2 Biology
Unit 1: Living Cells
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Learning Objectives
• Describe 2 ways in which chemical reactions can be speeded up.
• Name the products of the breakdown of hydrogen peroxide.
• State the general effect of a catalyst on the speed of a chemical reaction.
• Say what effect a reaction has on the catalyst.
• Say what effect a catalyst has on the energy input needed to start a reaction.
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Effect of heat on breakdown of hydrogen peroxide
• Hydrogen peroxide breaks down into water and oxygen
• Read through the experiment in your textbook
• Conclusions – The breakdown of hydrogen peroxide is promoted by
heat energy
– The rate of breakdown increases as the temperature increases
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The effect of manganese dioxide on hydrogen peroxide
• Make a copy of this diagram, and draw a diagram of what happens when this is demonstrated by the teacher.
– Which gas is given off?
– How can you test for this gas?
– The chemical symbol for hydrogen peroxide is H2O2 what else is produced?
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Results of manganese dioxide and hydrogen peroxide
• Oxygen gas and water are the products of this reaction.
• Manganese dioxide remains chemically unaltered by this reaction.
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Catalysts
• A chemical which speeds up the rate of a reaction and yet remains unaltered is called a catalyst.
• Catalysts lower the energy input (activation energy) required for a chemical reaction to proceed.
• Activation energy graph – Uncatalysed reaction
– Catalysed reaction
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Learning Objectives
• Give the general term for biological catalysts.
• Give the word equation for the reaction catalysed by the enzyme catalase.
• State where enzymes are found.
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Enzymes
• Enzymes speed up the chemical reactions that take place in our cells (biological catalysts).
• Enzymes are proteins and occur naturally in living cells
• Catalase is an enzyme which catalyses the breakdown of hydrogen peroxide
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The effect of catalase on hydrogen peroxide
• Explain the results of this experiment
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Importance of enzymes
• Enzymes allow biochemical reactions to proceed at relatively low temperatures
• Without enzymes, biochemical reactions would proceed so slowly that life would cease to exist.
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Pupil Activity
• Complete the testing your knowledge section on
– First edition – pg 43/44
– Second edition - pg
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Learning Objectives
• Name the type of chemical of which enzymes are composed.
• Describe a test for protein. • State the meaning of ‘specific’ as applied to enzymes. • Define the term substrate as applied to enzymes. • Describe the active site of an enzyme. • Explain the term complementary as applied to active sites. • Explain the specific nature of an enzyme in terms of its
active site.
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Specificity
• Active site
– Where the substrate attaches to the enzyme
– Is a specific shape determined by its chemical structure resulting from bonding between amino acids
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Lock and Key Theory
• Each enzyme is specific to one substance - its substrate
• The shape of the substrate molecule and the active site are complementary
• The enzyme and the substrate combine to form an enzyme-substrate complex
• The products then leave the active site leaving the enzyme unaltered
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Enzyme Reactions
• Breakdown (degradation) reactions • where one molecule breaks down into smaller
molecules
• Starch maltose
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Enzyme Reactions
• Building up (synthesis) reactions
– where molecules join together to make a larger molecules
– Glucose-1-phosphate starch
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Learning Objectives
• Define the term breakdown reaction.
• State the reason for the breakdown of starch by animals.
• Name the substrate and product of the enzyme amylase.
• Describe a test for starch.
• Describe a test for maltose sugar.
• Explain the need for a control in an investigation.
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Effect of amylase on starch
• Make a copy the diagram showing the action of amylase on starch (pg 45 Ed.1)
• What does tube A show?
• What is tube B for?
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Control
• A control is a copy of the experiment – All factors are kept exactly the same
– The factor being investigated is changed
• When comparing results – Any difference found must be due to one factor
• In enzyme experiments the control tube is usually water, or boiled enzyme solution
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Learning Objectives
• Define the term synthesis reaction.
• Name the substrate and product of the enzyme phosphorylase.
• Explain in terms of diffusion why plants store starch instead of glucose.
• Describe a phosphorylase experiment and its controls.
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Effect of phosphorylase on glucose-1-phosphate
• Make a labelled drawing of the diagram on pg47 (ed.1)
• Make conclusions from this experiment.
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Synthesis of starch
• Starch is synthesised from glucose. A starch molecule contains hundreds of glucose molecules.
• The enzyme phosphorylase can be used to speed up the synthesis of starch.
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Learning Objectives
• Describe the effect of increasing temperature on enzyme-catalysed reactions.
• Draw and interpret a line graph showing the effect of temperature on enzyme activity.
• Define the term optimum temperature. • State the optimum temperature for enzyme
reactions in the human body. • Describe the effect of high temperature on
protein structure. • Define the term denatured
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Factors affecting enzyme activity
• To function efficiently enzymes require
– Suitable temperature
– Suitable pH
– Adequate supply of substrate
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The effects of temperature on enzyme activity
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The effects of temperature on enzyme activity
• Very low temperature
– Enzymes inactive
• Low temperatures
– Enzyme and substrate molecules move slowly
– Few enzyme-substrate collisions
– Low enzyme activity
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The effects of temperature on enzyme activity
• Increasing temperature
– Enzyme and substrate molecules move faster
– More frequent enzyme substrate collisions
– More enzyme-substrate complexes (ESC) form
– Increasing rate of reaction
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The effects of temperature on enzyme activity
• Optimum temperature – Temperature at which the reaction works best – Usually 40oC
• Above this temperature – Atoms vibrate within the enzyme molecule – This breaks the chemical bonds that hold the amino
acids together – Enzyme molecule breaks apart changing the shape of
the active site – The enzyme becomes denatured – this is irreversible
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Planning and designing an investigation into the effect of temperature on the activity of lipase
• Read through the information provided in your textbooks (pg 53 – 1st edition)
• Complete the “what to do section” by using the guidance to design an investigation
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Learning Objectives
• Describe the pH scale. • State the pH levels of the mouth, stomach and small
intestine. • Define the term optimum pH. • Interpret data to identify the optimum pH for an enzyme. • State the optimum pH for pepsin. • State the optimum pH for trypsin. • Describe the colour change of Clinistix when exposed to
glucose. • Name the substrate and products of the enzyme invertase.
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The effects of pH on enzyme activity
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The effects of pH on enzyme activity
• pH refers to the concentration of hydrogen ions in a solution – More hydrogen ions, lower pH, more acidic
• One of the chemical bonds that hold enzymes in their specific 3D shape are hydrogen bonds
• If an enzyme is exposed to an unsuitable pH, these hydrogen bonds break and the enzyme becomes denatured.
• All enzymes have an optimum pH at which they work best.