Define the terms: catalyst, kinetic energy, limiting factor, energy transfer, yield, active site, substrate, enzyme, product, and enzyme-substrate complex.


A substance that increases the rate of a chemical reaction without itself underground any permanent chemical change.

Kinetic energy: 

The energy that an object possesses due to its motion.

Energy transfer: 

The process by which energy is relocated from one system to another, for example through the transfer of heat, work, or mass transfer.


A substance that acts as a catalyst in living organisms, regulating the rate at which chemical reactions proceed without itself being altered in the process.

Active site: 

A region on an enzyme that binds to a protein or other substance during a reaction.


A molecule acted upon by an enzyme.


The substances formed by chemical reactions. 

Enzyme-substrate complex: 

A temporary molecule formed when an enzyme comes into perfect contact with its substrate. 

Limiting factor: 

Anything that constrains a population’s size, and slows or stops it from growing.


The amount of an agricultural resource produced.

Denatured enzyme: 

A process in which the structure of an enzyme is altered due to exposure to certain chemical or physical factors (eg. heat, acid, etc.) causing the enzyme to become permanently inactive. 

Immobilized enzyme: 

Enzymes are physically confined or localized in a certain defined region of space with retention of their catalytic activities, which can be used repeatedly and continuously.

Describe the structure and function of enzymes

Structure of an enzyme

  • Made up of α amino acids linked together by amide peptide bonds in a linear chain.
  • The resulting chain is a polypeptide chain, also known as proteins.
  • The sequence of amino acids specifies the catalytic activity/ structure of the enzyme.
  • When heated, an enzyme’s structure denatures, resulting in a loss of enzyme activity.

The function of an enzyme

Enzymes control the rate at which chemical reactions occur in the body.

(e.g. the anabolic reaction of building muscle, or the catabolic action of breaking down food particles during the digestion process)

Explain what is meant by the lock and key theory

This theory suggests a mechanism that explains how enzymes react with the substrate. The enzyme is the “lock” which has a specific shape into which one type of substrate (the key) fits.

Discuss why the induced fit model is now used to describe the lock and key theory

The induced fit model is a model for enzyme-substrate interaction. It describes that only the proper substrate is capable of inducing the proper alignment of the active site and will enable the enzyme to perform its catalytic function. It also suggests that the active site will continue to change until the substrate is completely bound to it. The lock and key theory presents that enzymes are fixed and are not flexible.

Outline limiting factors of enzyme activity


  • At low temperatures, molecular movement is slow and thus there are less number of successful collisions between enzymes and substrates.
  • Reaction rates are slow due to the lower amount of collisions.
  • Too high temperatures can alter the shape and structure of the enzyme and thus denature it. 
  • Reaction rates are slow since less enzymes 
  • Enzymes will usually have a temperature that allows high reaction rates although that depends on the organism it is in.

pH levels

  • Extreme pH level changes can alter the shape and structure of an enzyme and denature it.
  • These changes are usually permanent
  • Enzymes will also have an optimum pH level.

Substrate concentration

  • Higher substrate concentration results in a higher rate of reaction 
  • This is a limiting factor.

Enzyme concentration

  • Higher enzyme concentration results in a higher rate of reaction
  • This is a limiting factor.

List 3 enzymes that function within the human body

  1. Protease: breaks down protein.
  2. Carbohydrase: breaks down carbohydrates.
  3. Lipase: Breaks down lipids.


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