Enzymes

• Describe what an enzyme is and structure

  Biological catalyst made of globular proteins

  The active site is specific and unique in shape due to the specific folding and bonding in the tertiary structure of the protein

  Due to this specific shape active site, enzymes can only attach ti substrates that are complementary under shape

  Enzyme catalyse intracellular and extracellular reactions. For example Catalase is an intracellular enzyme inside liver cells that break down hydrogen peroxide into oxygen and water.

  Trypsin is an extracellular enzyme in the small intestines, that hydrolyses proteins
• How do enzymes speed up chemical reactions?


  By lowering the activation energy (all reactions require a certain amount of energy before they occur , this is knows as activation energy).

  When enzyme attach to the substrate they can lower activation energy needed for reaction to occur and therefore speed up reaction
• Describe the lock and key model

  This models suggest that the enzyme is like a lock and the substrate is like a key that fits into it due to the enzyme specific tertiary structure resulting in a complementarity shape.

  The enzyme active site is a fixed shape and that due to the random collision the substrate can collide and attach to the enzyme forming an enzyme substrate complex and the charged group within the active site are thought to dissolve the substrate and therefore lower the activation energy.
• Describe the induced fit hypothesis

  This hypothesis suggest that enzyme is like a glove and the substrate is like your hand

  Induced fit is when the enzyme active site is induced or slightly changes shape to mould around the substrate. When the enzyme substrate complex occurs it puts strain on the bonds and therefore lowers the activation energy
• What are the factors affecting enzyme?

  Enzymes are globular proteins sensitive to certain conditions. The following conditions affect the rate of enzyme controlled reactions:

  -Temperature

  -PH

  -Enzyme concentration

  -Substrate Concentration
• Describe the shape of graph for temperature

  There is an increase in rate with temperature we reach our optimum, and there is a sudden decrease in rate at higher temperature.
• Explain the shape of graph for temperature affect on enzyme

  If the temperature is too low there is insufficient kinetic energy for successful collisions if the temperature is too high enzymes denatures and the active site changes shape and enzyme complexes cannot form

  High temperature causes bonds to break and the tertiary structure alters causing a change in shape of active site
• Describe the Q10 temperature coefficient


  Is a measure of the rate of change of enzyme controlled reaction as a result of increasing the temperature by 10 degrees

  Q10= R2/R1

  R1-rate of reaction at a temperature of X degrees

  R2-Rate of reaction a temperature (x+10) degrees
• Describe the effect of pH on enzyme activity

  Enzymes have an optimal pH level at which they can operate on an optimal level.

  Too high or too low pH will interfere with the charges in the amino acid in the active site causes ionic/hydrogen bonds to break alters tertiary structure and change the shape of the active site of an enzyme denatures
• Describe the effect of substrate concentration

  If there is a low concentration of substrate the reaction will be lower as there will be fewer collisions between the enzyme and substrate

  increasing the substrate concentration will increase the rate of reaction at high substrate concentration the rate of reaction of a plateau because all the active site are in use the enzymes are saturated
• Describe the effect of enzyme concentration in enzyme

  At low enzyme concentration there will be a lower rate of reaction increasing the enzyme concentration will increase the rate of reaction as enzyme substrate complexes will be more likely to form at high enzyme concentration unless unlimited substrate is added the rate of reaction plateaus as there will be a insufficient substrate to bind with a large number of enzymes
• How do competitive inhibitors affect enzyme activity?

  Competitive inhibitors are the same shape as the substrate and the complimentary in shape to the active site therefore they bind to the active site.

  This prevents the substrate from binding and enzyme inhibitor complexes form instead of enzyme substrate concentration and the rate of reaction is lower. Most competitive inhibitor is reversible. If a high enough concentration of substrate is added, the substrate can knock out the the inhibitor and therefore the rate of reaction will increase.

  Reversible means inhibitor can be removed whereas non reversible means Inhibitor cannot be removed from the enzyme.

  Lower activation energy at low substrate concentration but at high concentration they both plateau
• How do non competitive inhibitor affect enzyme activity?

  Noncompetitive inhibitor is bind to the enzyme away from the active site called the allosteric site

  This changes the active site to change shape and therefore the substrate can no longer bind regardless of how much substrate is added. Fewer enzyme substrate complexes to form and rate of reaction is lower and plateaus at lower rate, doesn't matter about substrate concentration
• What is an end product inhibition?

  The products of some reaction are reversible inhibitors for the enzymes involved in controlling the reaction. This enables the reaction to be controlled, if there is lot of products present, it will inhibit the enzyme and causes the reaction to slow or stop . This prevent resources being wasted
• Why is coenzyme, cofactors or a prosthetic group needed?

  Some enzyme controlled reactions require an additional non-protein molecule, such as coenzyme, cofactors or a prosthetic group, to catalyse a reaction
• What are coenzymes and cofactors?

  Some reactions require atoms to be carried from one reaction to the next in multistep pathways. Some enzymes also provide a non-protein molecule to bind to the active site to make it complementary to the substrate. these molecules are coenzyme and cofactors the difference is coenzyme are organic organic molecules and cofactors and inorganic molecule
• What are prosthetic groups?

  On enzyme Are a type of cofactors but they differ in that they are permanently attached to the enzyme by covalent or non covalent forces.
• What is precursor activation?


  Enzyme often occur in an inactive form and require activation by a type of cofactor but they differ in that they are permanently attached to enzyme this prevents enzymes from causing damage within cells and ensure they are only used when they are needed an enzyme is activated by the binding of a

  Cofactor as this causes a shape in the tertiary structure so that the active site becomes complimentary in shape to a substrate the precursor protein the inactive enzyme is also known as the

  Apoenzyme when it is activated by the binding of the cofactor it is known as the holoenzyme