Enzymes
Laura Armstrong
Teacher
Contents
Recall Questions
This topic requires prior knowledge of proteins. You can test your knowledge on these below.
Which level of protein structure gives it its 3D shape
Tertiary structure
What determines the 3D shape of a protein
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The sequence of amino acids in the primary structure.
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The position of R groups of amino acids determines the ionic, hydrogen bonds and disulphide bonds that determine the tertiary structure.
What type of reaction breaks down a dipeptide?
Hydrolysis reaction, water is added
What type of reaction forms a peptide bond?
Condensation reaction between two amino acids, water is produced.
Topic Explainer Videos
Check out this @LauraDoesBiology video that explains enzymes or read the full notes below. Once you've gone through the whole note, try out the practice questions!
What Are Enzymes?
- Enzymes are biological catalysts that speed up metabolic reactions without being used up.
- Enzymes reduce the activation energy of a reaction, making the reaction more likely to occur and therefore increasing the rate.
- Enzymes allow biochemical reactions to take place at much lower temperatures, for example the catalysis of starch at body temperature.
- They are globular proteins with a specific 3D tertiary structure determined by their amino acid sequence.
- Each enzyme has an active site, where the substrate binds to form an enzyme-substrate complex.
Lock and Key & Induced Fit Models
Lock and Key Model
- The active site is complementary to one substrate
- The substrate fits into the enzyme's active site exactly, like a key in a lock.
- The enzyme remains unchanged after the reaction.
- This model is now considered too simplistic as it does not explain flexibility in the active site or how the activation energy of the reaction is reduced.
Induced Fit Model
- The active site is not a perfect fit initially but changes shape slightly when the substrate binds.
- This leads to tighter binding and strains the bonds in the substrate, lowering activation energy. (alternatively reactants are held closer together overcoming any repulsive forces, lowering the activation energy)
- This model better explains how enzymes work in real biological systems.
Enzyme Action
1. Formation of Enzyme-Substrate Complex:
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The specific substrate binds to the enzyme’s complementary active site.
2. Lowering of Activation Energy:
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The enzyme strains bonds in the substrate, lowering the activation energy.
3. Product Formation:
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The substrate is converted into the product, which then leaves the active site.
4. Enzyme Reusability:
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The enzyme remains unchanged and can catalyse more reactions.
Key Terms
- Enzyme: A biological catalyst that speeds up reactions.
- Active site: The specific region where the substrate binds.
- Enzyme-substrate complex: A temporary structure formed when the enzyme binds to the substrate.
- Activation energy: The minimum energy required for a reaction to occur.
- Denaturation: The loss of an enzyme's shape due to high temperature or extreme pH.
No answer provided.
Exam Tips
Always refer to enzyme-substrate complex formation when explaining how enzymes function in exam answers.
Always refer to an enzyme's specific tertiary structure which determines the shape of its active site.
No answer provided.
Explain how the induced fit model of enzyme action allows reactions to happen at normal body temperature. (3 marks)
When the substrate binds, the active site changes shape to fit around it more tightly.
This places strain on the substrate’s bonds,
Lowering the activation energy and enabling the reaction.
Practice Question
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!