Enzymes

• Irreversible Inhibitors


  The effects of these inhibitors cannot be removed and the enzyme is permanently damaged.
• Reversible inhibitors


  When these are removed the enzyme can function as normal.
• How do substrate levels affect the action of a non-competitive inhibitor?

  An increase in substrate concentration does not reduce the effect of the inhibitor as the number of functioning enzymes has been permanently reduced.
• Explain how non-competitive inhibitors work

  The inhibitor attaches to another region of the enzyme (allosteric site)This causes the shape of the active site to change so substrates can not attach

  
• How do substrate levels affect the action of a competitive inhibitor?

  A competitive inhibitor has little effect when the substrate levels are high as the substrate out competes the inhibitor and attaches to the active site more often.
• What is a competitive inhibitor and how does it work?

  The inhibitor substance competes with the usual substrate for the active site.Competitive inhibitors are very similar in shape to the usual substrate.I

  
• What are enzyme inhibitors?

  Substances that interfere with enzyme action and reduce enzyme activity.

  
• Explain how pH changes the activity of an enzyme?

  Each enzyme has an optimum pHAt either side of the optimum pH enzyme activity is reduced.A change in pH disrupts the ionic bonds within an enzyme and so the shape of the active site changes and the enzyme becomes denatured.

  
• Optimum temperatures for animals and plants?

  Animal is around 40°CPlant is around 20°C
• What happens as the temperature rises more and more above the optimum?

  More and more bonds become broken until it is totally denatured.
• Explain what happens when the temperature of an enzyme controlled reaction is increased.


  1. The enzyme and substrate gain kinetic energy.2. The molecules move more and there are more successful collisions between enzymes and substrates so more enzyme-substrate complexes form.3. The optimum temperature is when collisions happen at their fastest rate.4. Above the optimum temperature the hydrogen bonds within the enzyme break and the active site changes shape and the enzyme is denatured so ES complexes cannot form.

  
• Explain what happens if substrate is supplied at a constant rate but the number of enzymes is increased.

  As more enzymes become available the rate of reaction increases as more enzyme substrate complexes can form.The rate of the reaction will only level off if substrates become limiting and this rarely happens.

  
• Explain why as substrate concentration increases the rate of an enzyme controlled reaction increases.

  There are more substrates to fill the available active sites.The rate levels off when all the available enzymes are working at their maximum rate.

  
• Sketch graph for rate of reaction and pH

  
• Sketch graph for enzyme rate of reaction and temperature

  
• Sketch graph for enzyme rate of reaction and enzyme concentration

  
• Sketch graph for enzyme rate of reaction and substrate concentration.

  
• List 5 factors that change enzyme activity

  1. Substrate Concentration2. Enzyme Concentration3. Tempertaure4. pH5. Presence of inhibitors
• What are Co-enzymes?

  These are a type of co-factor.They are non-protein organic molecules needed for enzyme action.e.g NAD and FAD in respiration.

  
• What are prosthetic groups?

  A type of co-factor e.g haem is a prosthetic group needed for the enzyme catalase to work.
• How does a co-factor like the calcium ion work?

  It forms an attachment to the enzyme which changes the shape of the active site and so enables a reaction to take place.
• What are co-factors?

  Non-protein substances that enzymes require to function

  
• What does the induced fit model propose?

  The active site of the enzyme very closely matches the shape of the substrate.The active site is flexible and moulds around the substrate.

  
• What is the lock and key model of enzyme action?

  The enzyme active site is an exact match to the shape of the substrate, they are exactly complementary

  
• How do enzymes lower activation energy?

  1. In anabolic (build up) reactions they orientate the substrates to facilitate bonding.2. In catabolic (break down) reactions they put the substrate under tension to facilitate the breaking of bonds.
• How do enzymes work?

  Substrates fit into the active site and form an enzyme-substrate complex.The substrate then is turned into product, the product no longer fits into the active site and is released.

  
• Activation Energy

  The energy barrier that must be overcome before a reaction can take place.Enzymes lower the activation energy and so reactions can take place more rapidly.

  
• Enzyme

  Biological Catalysts that speed up metabolic reactions.Globular proteins.Not changed by the reaction and can be re-used.

  
• How can enzyme inhibitors be used as biosensors?

  An inhibitor is made that will attach to the active site of a disease causing enzyme.The inhibitor is attached to diagnostic testing strip and the patient sample is added.The enzyme being monitored is captured by its active site and gives a positive read out.
• Pregnancy test

  The pregnancy testing strip contains antibodies and an enzyme.Pregnancy hormones in the urine which contain antigens attach to the enzyme-antibody complex and when activated the enzymes produce a colour change.
• General biosensor principle

  Molecule being monitored reacts with the immobilised enzymes and produces a colour change, which often can be changed into an electrical signal.
• Why are enzymes good biosensors?

  Because they are specific they can be used to identify individual molecules. They are also quantitative.
• When enzymes are used in a continuous flow reactor what should the flow rate of the substrate over the enzymes be like?

  Flow rate should be slow enough to allow the enzyme and substrate time to collide but fast enough to make sure collisions are happening at their fastest rates.
• Advantages of enzyme immobilisation.

  1. Enzymes are thermostable, more effective over a wider range of temperatures.2. Enzymes are more resistant to changes in pH3. Enzymes can be reused4. Commercial processes using enzymes can be continuous, which is faster and produces less waste.5. The product is not contaminated with enzymes so less purification of product is needed.

  
• Disadvantages of enzyme immobilisation

  1. Some of the enzymes active sites may be inaccessible2. The speed of diffusion between enzyme and substrate may be reduced.
• Cross-linkage

  The enzymes are bonded covalently to a matrix, such as cellulose, as a consequence of chemical reactions

  
• Encapsulation

  The enzymes are trapped inside a selectively permeable membrane such as Nylon.

  
• Entrapment

  The enzymes are trapped within polymers such as alginate beads or microspheres.

  
• Adsorption

  Enzymes are attached by weak forces to an inert substance such as glass or a matrix.

  
• 4 Methods of enzyme immobilisation

  1. Adsorption2. Entrapment3. Encapsulation4. Cross-linkage