Biological molecules - Enzymes

• Characteristics of enzyme

  • Speeds up chemical reactions
  • Enzymes lowers activation energy needed to start a reaction
  • Required in minute amounts
  • Enzymes remain unchanged at the end of reactions
  • Enzymes can be used over and over again
  • Small amount of enzymes can catalyse large number of reactions
• Characteristics of enzyme

  • Highly specific in their actions
  • Each reaction is catalysed by a unique enzyme
  • Affected by temperature
  • Affected by pH
  • Enzymes work best in slightly acidic/alkaline solutions
  • Drastic change in pH causes denaturation
• Characteristics of enzymes

  • Some enzymes catalyses reversible reactions
  • Can go in the forward/backward direction
  • Some enzymes catalyses both reactions till equilibrium is reached
  • Some enzymes need coenzymes for activity
  • Coenzymes are non-proteins organic compounds which are essential for enzyme activity
  • Some enzymes need coenzymes to be bound to them in order for them to catalyse reactions
• How enzymes lower activation energy

  • Enzymes do not affect change in free energy
  • Enzymes only hastens reactions that will occur eventually
  • The starting point to the highest point of the graph is the activation energy
• Enzyme specificity

  • Limitation of activity of enzyme on specific substrate/reaction/type of reaction
  • Papain
  • Catalyses the hydrolysis of peptide bonds in many locations
  • Thrombin
  • Catalyses the hydrolysis of peptide bonds adjacent to the arginine
  • Primarily found in proteins essential for blood clotting
  • Catalase
  • Almost specific to the break down of hydrogen peroxide
• Common enzymes

  1. Protease
  2. Bio-active detergents which remove protein stain
  3. 2. Pectinase
  4. Help with the extraction of fruit juices by breaking down pectin
  5. 3. Lactase
  6. Help break down lactose to glucose and galactose
• Lock and key hypothesis

  • Enzyme has a particular shape in which the substrate fits exactly
  • Enzyme is the lock, which has a complimentary shape to the substrate which is the key
  • Substrate binds itself to the active site of the enzyme
  • The product that is formed is no longer able to fit into the active site of the enzyme and escapes into the surrounding medium, leaving the active site
  • Enzyme is free to take part in other reactions
• Induced fit model

  • Enzyme alters shape of active site to fit around the substrate
  • A new product leaves the active site
  • Enzyme free to take part in other reactions
• Induced fit hypothesis

  • Some enzymes and their active sites are physically flexible structures
  • This means that active site of enzyme does not have to begin with a complimentary shape to the substrate
  • Binding of substrate to the active site causes small conformational change to enzyme
  • This allows the substrate to fit more snugly + allows the enzyme to perform its catalytic function more effectively
• Effects of temperature

  • When temperature increases, kinetic energy of substrate and enzyme molecules also increases
  • Number of effective collision between substrate and enzyme increases, causing more enzyme substrate complex to be formed
  • Rate of reaction roughly doubles for every 10 degrees until optimum temperature is reached
  • Optimum temperature is when enzyme has the maximum rate of reaction
  • At this point of time, temperature can go back and fourth and enzyme will still be alright
  • Once temperature exceeds optimum temperature, enzyme activity decreases as enzymes becomes denatured
• Enzyme denaturation

  • Excessive heat disrupts intracellular bonds which hold the secondary and tertiary structure of the enzyme
  • Enzyme unfolds and loses its precise shape of active site
  • Destruction of structure of enzyme is irreversible
  • When temperature is reduced near/below freezing point, enzyme becomes inactivated
  • Enzyme activity very low
  • Enzyme can regain catalytic influence when higher temperature is restored
• Effects of pH on enzyme activity

  • Optimum pH = Maximum rate of reaction
  • Intermolecular bonds which hold the tertiary structure of the enzyme remain intact
  • Conformation of active site most ideal for substrate attachment
  • Number of effective collision between substrate and enzyme is the highest, causing the most number of enzyme-substrate complex to be formed
  • When pH higher/lower than optimum pH, H^+ concentration changes
  • Ionic charges on basic and acidic groups of side chains of amino acids residules changes
  • Ionic bonding which maintains the conformation of active site is disrupted
• How enzyme concentration affect enzyme activity

  • When enzyme concentration increases, number of effective collision increase
  • More enzyme-substrate complex formed
  • After a while, rate of reaction levels off as substrate become limiting factor
  • Not all enzymes have substrate attached
• How substrate concentration affects enzyme activity

  • When substrate concentration increases, number of effective collision between enzyme and substrate increases
  • More enzyme-substrate concentration formed
  • Reaction rate levels off
  • Enzyme becomes limiting factor
  • All enzyme already have substrate
• How enzyme inhibitors affect enzyme activity

  • Inhibitors can be reversible/irreversible
  • Reversible
  • Inhibitor not permanently bound to enzyme and can leave enzyme, restoring it to uninhibited level of activity
  • Irreversible
  • Inhibitor permanently bound to enzyme and enzyme permanently inhibited
  • Two types
  • Competitive and non-competitive
• Competitive inhibitor

  • Inhibitor has close structural resemblance to substrate
  • Inhibitor competes with substrate for active site
  • Inhibitor may remain permanently bound to enzyme, excluding substrate while remaining attached to active site
  • Effects can be reduced by increasing substrate concentration
  • Increases chances of enzyme-substrate collision rather than enzyme-inhibitor collision
• Non-competitive inhibitor

  • Inhibitor no structural resemblance to substrate
  • Combines itself to regions of enzyme other than active site
  • Puts proportion of enzyme molecules out of action
  • Changes conformation of enzyme molecule and active site
  • Less likely for enzyme to catalyze reaction
  • Reaction rate never reaches maximum even when substrate concentration increases
• What are enzymes

  • Biological catalysts mainly made up of proteins
  • Speeds up chemical reactions being chemically changed at the end of the reaction
• Functions of enzyme

  • Synthesis of complex substances
  • Break down food substances in cells to provide energy
  • Break down poisonous substances in cells
• Factors affecting enzyme function

  1. Enzyme concentration
  2. Substrate concentration
  3. Temperature
  4. pH
  5. Salinity
  6. Activators
  7. Inhibitors