Enzymes

• What are enzymes?

  Globular protein with a specific tertiary structure

  Biological catalysts

  Converts substance into products
• What is an intracellular enzyme?

  Catalase
• What is an extracellular enzyme?

  Trypsin
• What do enzymes do to activation energy?

  They lower it by taking an alternative energy pathway
• What happens to enzymes with this activation energy?

  There are more successful collisions, more enzyme substrate complexes, more enzyme product complexes, increased rate of reaction
• What happens to collisions between enzyme and substrate molecules, if the temperature is increased?

  Gain kinetic energy and move faster

  More successful collisions

  Higher amount of formation of enzyme substrate complexes

  Higher rate of reaction

  Higher amount of enzyme product complexes formed per second
• What is the optimum temperature?

  The temperature where the enzyme is working at the fastest rate
• What happens when the enzyme denature, at a higher temperature?

  Molecules move faster

  May break some weak bonds like the hydrogen bonds and ionic bonds, which holds the tertiary structure

  Active site changes - not complementary to the substrate

  Substrate doesn't fit well

  Decreased rate of reaction
• Does every catalysts have the same optimum temperature?

  No, some work best at cool temperatures or in very hot conditions
• What is the temperature coefficient Q10?

  Rate of reaction at (T+10) / Rate of reaction at T
• What happens if Q10, at higher temperatures, is less than 2?

  It is said that the enzyme is denaturing
• How are changes in pH affect enzymes?

  H+ ions are attracted to negatively charged molecules

  Interact with ionic bonds

  Interferes with the binding of the substrate molecule to the active site

  Slow rate of reaction, as shape of active site is disrupted

  If pH restored, the hydrogen bonds can reform and active site's shape is restored.

  Extremes - can't be restored
• What are examples of enzymes working at different pH?

  Maltose - 6-8

  Pepsin - 1-2
• Describe the enzyme concentration against initial rate of reaction graph

  As the concentration of enzyme increases, the initial rate of reaction increases, until the initial rate of reaction becomes constant.

  
• Explain the enzyme concentration against initial rate of reaction graph

  More successful collisions between substrate and enzymes because there's more active sites

  The rate is constant after because the enzymes are in excess and the enzyme substrate is the limiting factor

  
  

  Substrate concentration is the limiting factor.
• Describe the substrate concentration against initial rate of reaction graph

  As the concentration of substrate increases, the initial rate of reaction increases, until the initial rate of reaction becomes constant.
• What is the point of saturation?

  It is the point where every possible active site of an amount of enzymes is being used and is binded to substrate, so the rate of reaction will no longer increase. Works both ways enzyme and substrate concs.
• Explain the substrate concentration against initial rate of reaction graph

  Higher concentration of substrate means that there are more collisions with the substrate and the active site, means there are more enzyme substrate complexes, more enzyme product complexes

  
  

  Substrate concentration is in excess, and the active site is always occupied. Reached V-max, when enzymes is working at its capacity.

  Enzyme concentration is the limiting factor.
• What happens to enzymes at lower temperature?

  Low thermal and kinetic energy

  Fewer successful collisions

  Fewer enzyme substrate complex

  Fewer enzyme product complex
• What are inhibitors?

  A substance which reduces the rate or stops a reaction
• What is a competitive inhibitor?

  A molecule with a similar shape to the substrate, allowing it to occupy the active site of the enzyme.

  
  

  Fits into the active site so a substrate molecule can't enter.

  
  

  Amount of inhibition depends on the relative concentration of substrate and inhibitor molecule. More inhibitors - greater effect.

  
  

  Enzyme - inhibitor complex are formed.

  
  

  Reduces the rate of formation of enzyme substrate complexes and enzyme product formation

  
• Hoe can you "dilute" the effect of competitive inhibitor?

  As collisions are random and it's reversible, increasing the substrate concentration, it decreases the effect of reversible competitive inhibition.

  
  

  More chance of an enzyme molecule colliding with a substrate molecule than an inhibitor
• What is an inactivator?

  A competitive inhibitor which binds irreversibly to the enzyme's active site
• What happens when a non competitive inhibitor is placed?

  Binds to the allosteric site, away from the active site, irreversibly

  
  

  Don't compete with the substrate molecules for a place on the enzyme.

  
  

  Disrupts the enzyme's tertiary structure and change the active site shape

  
  

  Not complementary

  
  

  Rate of reaction decreases

  
• What is a cofactor?

  A non-protein substance. Binds to active site on enzyme, allowing substrate to fit into active site.
• What are prosthetic groups?

  Non-protein component in a protein, e.g. iron containing haem group in haemoglobin.
• Give examples in prosthetic groups

  Carbonic anhydrase needs a zinc ion

  Amylase needs a chlorine ion
• What are co-enzymes?

  Small organic molecules bind temporarily before at the same time or before as the substrate, like FAD, NADP and NAD
• How does pencillin work?

  Inhibits an enzyme in the bacterial cell wall
• How does cynanide work?

  Inhibits ATP
• How does venom from green mamba work?

  Inhibits acetylcholinesterase, leading to paralysis

  
  

  Inhibits respiration and catalase
• What is the lock and key model?

  This model proposes that enzymes work in the same way as a key operates only a single lock. A substrate will only fit the active site of one particular enzyme.
• What is the induced fit model?

  Substrate enters an enzyme's active site and the enzyme alters its shape slightly so the substrate can fit - conformational change
• What is end-product inhibition?

  When the final product in a metabolic pathway inhibits an enzyme that acts earlier on in the pathway, by binding to the allosteric site.

  
  

  Negative feedback