Enzyme Action
Biology: Cambridge International A Level, topic 3.1.1
Function of Enzymes
Metabolism is the different processes that take place in living organisms to allow them to survive. Enzymes are the proteins that catalyse (speed up) these reactions, they are biological catalysts.
Catalysts
- Enzymes are called biological catalysts because they speed up reactions in living organisms.
- E.g. Rubisco in plant cells catalyses the fixation of CO2 in photosynthesis.
- E.g. Amylase in your saliva catalyses the break down of starch to sugars when you eat.
Effect on the organism
- Enzymes speed up reactions that affect the organism on the cellular and individual level.
- E.g. Enzymes catalyse photosynthesis that takes place in cells. The products of photosynthesis (fixed carbon) are used around the plant on the organismal level to grow roots and shoots.
Structure and function
- Enzymes speed up reactions that affect both structure and function.
- E.g. Enzymes catalyse the production of collagen, a structural protein in bones.
- E.g. Enzymes catalyse respiration, the reaction that produces ATP.
Models of Enzyme Action
Models of enzyme action have changed over time. For many years, it was thought that enzymes worked in a lock and key manner. The induced fit model is now more widely accepted.
The lock and key model
- The lock and key model was originally used to explain enzyme action.
- The model proposes that the enzyme and substrate fit together perfectly.
- The substrate is a key fitting into a lock (the enzyme).
The induced fit model
- The induced fit model suggests there is a more dynamic interaction between enzyme and substrate.
- The model states that as an enzyme and substrate come together, their interaction causes a small shift in the enzyme’s structure.
- The shift means that the enzyme and substrate can bind to form an enzyme-substrate complex and catalyse a reaction.
- This model is now more widely accepted.
Enzyme-Substrate Complexes
Enzymes bind with substrates to form an enzyme-substrate complex in a specific fashion. The specificity of enzymes is determined by two things:
Active site
- Every enzyme only catalyses one specific reaction.
- Every enzyme has a specific active site that is complementary to the specific substrate.
- This jigsaw puzzle-like match between an enzyme and its substrates is what makes enzymes highly specific.
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Environmental factors
- The 3D, tertiary structure of the polypeptide chain determines the shape of the active site.
- Environmental changes can change the tertiary structure of the active site and can stop the enzyme from working properly.
- This is called a denatured enzyme.
Test yourself on Enzyme Action
Which of the following statements about the function of enzymes are true?
What type of biological molecule are enzymes?
What is the name of the model of enzyme action shown below?
Which of the following statements about models of enzyme action are true?
What is the name given to enzymes that have experienced a change in their active site due to environmental factors?