Lesson 13

State that enzymes are globular proteins with a specific tertiary structure

State that enzymes catalyse metabolic reactions

State that enzyme action may be extracellular or intracellular

State that enzymes catalyse metabolic reactions

Describe the mechanism of enzyme action Explain what is meant by enzyme-substrate

complex and enzyme-product complex Describe how enzymes lower activation energy Explain the importance of coenzymes and

cofactors in enzyme controlled reactions

Look at the two jellies, what has happened and why?

Think, pair, share

Enzymes are globular proteins with a specific tertiary structure

Enzyme action may be intracellular or extracellular

Enzymes are biological catalystsEnzymes catalyse metabolic reactionsEnzymes lower activation energy because

of the way the active site is shaped to fit the substrate

Use the plasticene to model the lock and key model of enzyme action

They are proteins of high molecular weight

They are biological catalysts

They are sensitive to temperature changes being denatured at high temperatures

They are sensitive to pH

They are generally specific in the reactions they catalyse

Enzymes possess an active site within which chemical reactions take place

Substratemolecule inthe ACTIVESITE

Enzyme molecule

The Active Site

Substratemolecules(complementaryshape to activesite)

Enzymemolecule

Productmoleculesdiffuse awayfrom theactive site

Substrate molecules bind with enzyme molecules at the activesite as a consequence of their complementary shapes. This is the basis of the LOCK AND KEY MODEL of enzyme activity

Enzyme substrate complexes form

Activesite

Reactionoccurs

Read page 127 in the text book Create a comparison table for lock and

key and induced fit hypothesis

Lock and Key Model Induced Fit Hypothesis

The Lock And Key Model

In an enzyme - catalysed reaction, the enzyme bindsto the substrate to form a complex

An enzyme - substrate complexforms

A reactionoccursforming anenzyme - productcomplex

Products diffuseaway from theactive site

Enzymemolecule

The lock & key modelproposes that the substratebinds to the active sitewhich it fits exactly, like akey in a lock

S

The Induced Fit Model

This model takes into account the fact that proteins (enzymes) have some three-dimensional flexibility

SUBSTRATE

Substrate binds to the enzymeat the active site

Binding of the substrateinduces the enzyme to changeshape such that there is anexact fit once the substratehas bound

Enzyme Molecule According to this model, reactions canonly take place AFTER induced fit has occurred

Specificity, The active site of an enzyme is a specific shape,

depending on the reaction that it catalyses, meaning that other molecules won’t fit into the active site

Active site, The area on an enzyme to which the substrate

binds Lock and key hypothesis,

The theory of enzyme action in which the enzyme active site is complementary to the substrate molecule, like a lock and key

Induced-fit hypothesis, The theory of enzyme action in which the

enzyme molecule changes shape to fit the substrate molecule more closely as it binds to it

Enzyme-substrate complex, The intermediary formed when a substrate

molecule binds to an enzyme molecule Enzyme-product complex

The intermediate structure in which product molecules are bound to an enzyme molecule lowering of activation energy

Answer the following questionDescribe the mechanism of enzyme action

Use as many key terms as possible Person with the most key terms used

correctly wins a prize

Swap answers Highlight all the key terms in their response

Enzyme Substrate Enzyme substrate complex Enzyme product complex Product Collision Active site Lock and key Induced fit

Maximum mark of 9, lose a mark for every incorrectly used term or missed term

Cofactor: substance that must be present for enzyme controlled reactions to take place at the appropriate rateProsthetic group: inorganic ion that is a

permanent part of the enzyme contributing to its 3D shape

Coenzyme: organic molecule that binds either just before or at the same time as the substrate (help reactions take place in sequence)

Inorganic ions: either bind to enzyme or substrate to help form the enzyme substrate complex

Role play, model or draw the effect of coenzymes and cofactors in enzyme controlled reactions

State that enzymes are globular proteins with a specific tertiary structure

State that enzymes catalyse metabolic reactions

State that enzyme action may be extracellular or intracellular

State that enzymes catalyse metabolic reactions

Describe the mechanism of enzyme action Explain what is meant by enzyme-substrate

complex and enzyme-product complex Describe how enzymes lower activation energy Explain the importance of coenzymes and

cofactors in enzyme controlled reactions

One form of COPD develops because enzymes are released by phagocytes entering the alveoli. This enzyme action can break down elastin in the lining of the bronchioles and alveoli. Use the example of elastin breakdown to explain the induced-fit hypothesis of enzyme action [5]

elastin is substrate (elastin / substrate) binds to / fits into , active site ; active site / enzyme / elastase / substrate / elastin,

shape changes idea of closer fit (between active site and

substrate) more bonds form (between substrate and active

site) forms enzyme-substrate-complex / ESC idea that (change in shape of active site)

destabilises / weakens , bonds (in substrate) / substrate

activation energy reduced idea of further shape change of, active site /

enzyme, after products form

Make a glossary of key enzyme terms