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What is an Enzyme?

Enzymes are biological catalysts that speed up the rate of chemical reactions without being changed or used up in the reaction.

Enzymes are necessary to all living organisms as of all metabolic reactions at a rate that can sustain life.

Enzymes are specific to one particular substrate.


Are enzymes proteins?



Are enzymes specific to one particular substrate?



What is the optimum temperature for enzymes to work?

37 C


When do enzymes denatured?

Enzymes denatured because high temperature destroys their site.


What effect does low temperature have on enzymes?

Low temperatures do not denature enzymes- that just makes them work more slowly.


How can enzyme activity be changed?

By altering pH and temperature


What is the substrate?

A chemical that enzymes act upon


Explain how enzymes fit into substrates

They fit into the active site of the substrate. E.g lock and key


What are the types of digestive enzymes?



Which enzyme digests starch and what does it produce?

Starch digested by amylase --> maltose

Amylase- salivary or pancreatic


What enzyme digests maltose and what is the product ?

Maltose digested by maltase --> glucose


What digests protein and what is the product?

Protein digested by proteases --> amino acids

Proteases e.g pepsin


What enzyme digests lipids and what is the product?

Lipids digested by Lipases --> fatty acids & glycerol


Describe enzyme specificity.

Enzymes are specific to one particular substrate(s) as the active site of the enzyme, where the substrate attaches, is a complementary shape to the substrate.
This is because the enzyme is a protein and has a specific 3-D shape
This is known as the lock and key hypothesis
When the substrate moves into the enzyme’s active site they become known as the enzyme-substrate complex
After the reaction has occurred, the products leave the enzyme’s active site as they no longer fit it and it is free to take up another substrate


Effect of Temperature on Enzyme Function

Enzymes work fastest at their ‘optimum temperature’ – in the human body, the optimum temperature is 37⁰C
Heating to high temperatures (beyond the optimum) will break the bonds that hold the enzyme together and it will lose its shape -this is known as denaturation
Substrates cannot fit into denatured enzymes as the shape of their active site has been lost
Denaturation is irreversible – once enzymes are denatured they cannot regain their proper shape and activity will stop
Increasing the temperature from 0⁰C to the optimum increases the activity of enzymes as the more energy the molecules have the faster they move and the number of collisions with the substrate molecules increases, leading to a faster rate of reaction
This means that low temperatures do not denature enzymes, they just make them work more slowly


Effect of pH on Enzyme Function

If the pH is too high or too low, the bonds that hold the amino acid chain together to make up the protein can be destroyed
This will change the shape of the active site, so the substrate can no longer fit into it, reducing the rate of activity
Moving too far away from the optimum pH will cause the enzyme to denature and activity will stop