Enzymes

• Proteins and Enzymes

  Enzymes are part of the group of chemicals called proteins. Proteins, along with carbohydrates and fats, are the chemicals that make up most of the diet of animals. 

  
  

  Proteins can be fibrous or globular, each with a different function.

  
  

  Fibrous proteins form the structural elements of the body, such as, collagen in muscles and tendons, and keratin in hair, horns and nails.

  
  

  Globular proteins are proteins that carry out many of the regulatory processes of the body, such as, hormones, transporters (haemoglobin) and enzymes. 
• Enzymes

  Enzymes act as biological catalysts, controlling the speed of a chemical reaction within all organisms. It increase the rate of a chemical reaction by providing an alternative reaction pathway. This lowers the activation energy required for the reaction to take place

  
  

  Enzyme reactions can make larger molecules from smaller molecules (anabolic reactions) or can break down large molecules into smaller ones (catabolic reactions).

  
• Enzyme Function

  Enzymes are very specific. For example, one enzyme catalyses (speeds up) only one type of reaction. 

  
  

  This is because enzymes have a very specific shape, determined by the sequence of amino acids they are made up of.

  
  

  The shape of the enzyme in an area known as the active site corresponds to that of the substance(s) it catalyses.

  
• Enzyme Reaction Overview

  • The substrate(s) binds to the active site of the enzyme.
  • The enzyme and substrate(s) form an enzyme-substrate complex. 
  • Once the reaction has occurred (anabolic or catabolic), the product is released from the enzyme.
  • The enzyme is not used up in the reaction, it continues to catalyse other reactions of the same type. 

  
• Enzyme Reaction Overview

  A) Substrate

  B) Active SIte

  C) Enzyme

  D) Enzyme-Substrate Complex

  E) Product

  
• Lock and Key Model


  The substrate and enzyme fit together perfectly, just as a lock and key do.

  
• Induced Fit


  The substrate and active site undergo slight changes to ensure an optimal fit.

  
• Factors that Affect Enzymes

  Enzymes have optimal conditions at which they work most effectively. When internal body conditions deviate from these optimum values, enzymes are less effective, causing less effective metabolic reactions in the body.

  
  

  Enzymes are affected by changes in temperature and pH levels, as well as the presence of cofactors and inhibitors.

  
• Factors that Affect Enzyme - TEMPERATURE

  Similarly to most chemical reactions, the rate of enzymatic reactions will increase as the temperature increases. 

  
  

  Increasing the temperature is only effective to a certain temperature, known as the optimum temperature.
• Factors that Affect Enzyme - TEMPERATURE

  As the temperature increases past the optimum temperature, the enzyme will denature. This means that the active site of the enzyme may change shape permanently, meaning that its specific substrate can no longer fit, and the enzyme can no longer catalyse reactions. 

  
• Factors that Affect Enzyme - pH

  pH is a measure of how acidic or basic a solution is. A low pH indicates that the solution is acidic, whereas a high pH indicates the solution is basic. 

  
  

  As proteins and enzymes are folded specifically, a change in the pH of the enzymes surrounding environment can affect the charges (positive or negative) on an enzyme.
• Factors that Affect Enzyme - pH

  The enzyme can uncoil and unfold, changing the shape of the active site. The substrate may also be affected by the pH, therefore, the enzyme and substrate can no longer fit together to carry out the reaction.

  
• Factors that Affect Enzymes - Cofactors

  Cofactors are substances that enzymes need present in order to work properly. 

  
  

  A cofactor will bind to the active site of the enzyme, enabling the substrate to bind effectively. The cofactor participates in the catalysis, but is not used up in the reaction and can be used again.

  
• Factors that Affect Enzymes - Inhibitors

  Inhibitors are substances that bind to an enzymes and prevent the enzyme from catalysing a reaction.

  
  

  There are two types of Inhibitors:

  1. Competitive Inhibitors
  2. Non-competitive Inhibitors
• Factors that Affect Enzymes - Inhibitors

  Competitive inhibitor - Binds to the active site of the enzyme, preventing the substrate from effectively binding. 

  
  

  Non-competitive inhibitor - Binds to another location on the enzyme (not the active site) and distorts the active site of the enzyme, preventing effective binding of the substrate.