Module 2.1.4- Enzymes

• Role of enzymes

  To catalyse reactions that affect metabolism at a cellular and whole organism level. They affect both structure and function.
• Anabolic reactions


  build up large chemicals and require energy
• Catabolic reactions


  break down large chemicals and release energy
• Mechanism of enzyme action

  has to be in the right orientation when colliding

  decreases the activation energy
• Lock and key hypothesis


  The idea that the tertiary structure of the enzyme has an active site which only fits a specific substrate molecule.

  when substrate binds with the active site an enzyme-substrate complex is formed

  when substrate/s react the products are formed in an enzyme-product complex

  
• How do enzymes work to decrease the activation energy

  R groups within the active site of the enzyme will interact with the substrate forming temporary bonds. These put a strain on the bonds within the substrate decreasing the activation energy.
• Enzyme substrate complex


  A temporary complex formed when an enzyme binds to its substrate molecule(s).
• Enzyme product complex


  complex formed as a result of an enzyme-catalysed reaction, when a substrate is converted to a product or products while bound to the active site of an enzyme.
• Induced fit hypothesis


  States that the partial binding of a substrate to an enzyme alters the structure of the enzyme so that its active site becomes complementary to the structure of the substrate, enabling binding.
• Intracellular enzymes


  Enzymes that function within cells
• Catalase- intracellular enzyme


  breaks down hydrogen peroxide to oxygen and water quickly, preventing its accumulation
• Extracellular enzymes


  Enzymes that are synthesised and secreted to work outside the cell.

  e.g. digestive enzymes are released outside of the cells to break products down so they are small enough to be absorbed
• Digestion of starch

  Begins in the mouth and continues in the small intestine.

  1. Starch polymers are partially broken down into maltose, a disaccharide. The enzyme involved is amylase. Amylase is produced in the salivary gland and the pancreas. Its released in saliva into the mouth, and in pancreatic juice into the small intestine.

  2. Maltose is broken down into glucose, a monosaccharide. The enzyme involved is maltase. Maltase is present in the small intestine.Glucose is small enough to be absorbed into the cells lining the digestive system = can be absorbed into the bloodstream
• What 2 enzymes are involved in the breakdown of starch


  Amylase and Maltase
• Amylase


  Enzyme in saliva that breaks the chemical bonds in starches into maltose
• Maltase


  A digestive enzyme that breaks maltose into glucose.
• Trypsin (protease)


  an enzyme from the pancreas that digests proteins into smaller peptides in the small intestine
• Vmax


  maximum initial velocity or rate of an enzyme-catalysed reaction.
• Increasing temperature of an enzyme controlled reaction...


  increases KE of particles, so move faster and collide more frequently so more frequent successful collisions increasing rate of reaction.
• Temperature coefficient Q10


  a measure of how much the rate of a reaction increases with a 10 °C temperature increase.

  
• Denaturation from temperature

  high temp = increases vibration, too high = bonds break = change in tertiary structure = active site changes shape = substrate cant fit = denature.
• Change in enzyme activity with temperature graph

  
• Change in enzyme activity with pH graph


  property that can alter the shape of an enzyme, each has an optimal and any deviation can decrease the enzyme activity symmetrical graph

  
• How does pH affect enzyme activity?


  change in pH refers to [H+]. These ions interact with polar and charged groups changing the degree of this interaction aswell as between other R groups.
• Increasing concentration of substrate on enzyme activity


  Increase of substrate molecules leads to higher collision rate with active sites of enzymes and formation of more enzyme-substrate complexes

  At one point all active sites will become saturated and so no more enzyme-substrate complexes can be formed.

  
• Inhibitor


  Prevents enzymes from carrying out their normal function of catalysis
• Competitive inhibitor


  a molecule with a structure similar to the substrate that inhibits enzyme action by competing for the active site

  Decreases rate of reaction but Vmax remains the same

  
• Example of competitive inhibitor

  Statins- reduce blood cholesterol concentration
• Non-competitive inhibitor


  The inhibitor binds to the allosteric site and causes the tertiary structure of the enzyme to change. Doesn't compete for the active site and substrate can no longer bind complementarily to the active site.Vmax decreases

  
• End-product inhibition


  used for enzyme-inhibition that occurs when the products of a reaction acts as an inhibitor to the enzyme that produces it.
• Cofactor


  Non-protein helpers that may be bound tightly to the enzyme as a permanent resident, or may bind loosely and reversibly along with the substrate.

  e.g. Zn2+ etc
• Cofactor for amylase


  Cl- catalyses breakdown of starch
• Coenzyme


  an organic cofactor

  e.g. NAD
• Prosthetic groups (cofactors)


  small molecules or ions that bind in the active site of an enzyme and required by certain enzymes to carry out their catalytic function
• Cofactor for carbonic anhydrase


  Zn2+

  enzyme for the metabolism of carbon dioxide
• Precursor activation


  When a precursor enzyme (that is inactive) undergoes a change in shape (particularly in tertiary structure) to be activated. This can be done by the addition of a cofactor
• Name of a precursor protein that does not have a cofactor group added yet

  Apoenzyme
• Name of a precursor protein with added cofactor group (activated)

  Holoenzyme
• Zymogens


  digestive enzymes secreted as inactive proteins, converted to active enzymes by removing some of their amino acids