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Biology · Class 9 · Chapter 6: Enzymes

8 min

Key points

Enzymes are biological catalysts that speed up biochemical reactions without being consumed
All enzymes are proteins made up of amino acids joined by peptide bonds
Enzymes work by lowering the activation energy required for reactions to occur
The active site is the specific region where substrate binds to the enzyme
Enzyme activity is affected by temperature, pH, enzyme concentration and substrate concentration
Optimum temperature for human enzymes is 37°C (body temperature)
Denaturation occurs when enzymes lose their shape due to high temperature or extreme pH
Lock and key model explains how enzymes are specific to their substrates
Cofactors and coenzymes help enzymes function properly
Enzyme inhibition can be competitive or non-competitive

Definitions

Enzyme: Enzymes are biological catalysts that speed up the rate of biochemical reactions without being consumed in the reaction.
Active Site: The active site is a specific region on the enzyme where the substrate binds and the reaction takes place.
Substrate: A substrate is the reactant molecule on which an enzyme acts to form products.
Denaturation: Denaturation is the process in which enzymes lose their natural shape and activity due to high temperature or extreme pH.
Cofactor: Cofactors are inorganic substances like metal ions that help enzymes to function properly.

Worked example

Define enzymes. Explain how temperature affects enzyme activity. Give two examples of enzymes with their functions. (6 marks)

Enzymes are biological catalysts that speed up biochemical reactions without being consumed in the process. They are proteins in nature. Temperature affects enzyme activity because enzymes work best at optimum temperature (37°C for human enzymes). At low temperatures, enzyme activity is slow. At high temperatures, enzymes denature and lose their shape. Examples: (1) Pepsin - digests proteins in stomach (2) Amylase - breaks down starch into sugar.

Common mistakes

Students confuse enzymes with hormones - remember enzymes are catalysts, hormones are chemical messengers
Writing that enzymes are consumed in reactions - they are NOT consumed, they are reused
Forgetting to mention that all enzymes are proteins in definitions
Confusing cofactors (inorganic) with coenzymes (organic)
Not explaining that denaturation is irreversible process

Quick recap

Enzymes are protein biological catalysts that speed up reactions without being consumed. They work best at optimum temperature and pH, and denature at high temperatures. Key examples include pepsin (protein digestion), amylase (starch breakdown), and lipase (fat digestion). Lock and key model explains enzyme specificity.

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