Enzyme Action

Intermediate 2 Biology

Unit 1: Living Cells

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.

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

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?

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.

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

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.

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

The effect of catalase on hydrogen peroxide

• Explain the results of this experiment

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.

Pupil Activity

• Complete the testing your knowledge section on

– First edition – pg 43/44

– Second edition - pg

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.

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

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

Enzyme Reactions

• Breakdown (degradation) reactions • where one molecule breaks down into smaller

molecules

• Starch maltose

Enzyme Reactions

• Building up (synthesis) reactions

– where molecules join together to make a larger molecules

– Glucose-1-phosphate starch

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.

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?

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

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.

Effect of phosphorylase on glucose-1-phosphate

• Make a labelled drawing of the diagram on pg47 (ed.1)

• Make conclusions from this experiment.

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.

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

Factors affecting enzyme activity

• To function efficiently enzymes require

– Suitable temperature

– Suitable pH

– Adequate supply of substrate

The effects of temperature on enzyme activity

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

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

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

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

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.

The effects of pH on enzyme activity

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.