factors affecting enzyme action

• Enzymes are examples of biological catalysts. They are specific to certain substrates. This is due to their complimentary active site. When substrates bind to the enzymes at this site an enzyme substrate complex forms. As enzymes are catalysts they are able to speed up a reaction without being used up.
• Although induced fit is very similar, in the induced fit model the enzyme and substrate interact with each other:

  The enzyme and its active site can change shape slightly as the substrate molecule enters the enzyme= conformational change. The conformational changes ensure an ideal binding arrangement between the enzyme and substrate is achieved. This maximises the ability of the enzyme to catalyse the reaction
• Enzymes are proteins that act as catalysts by providing an alternative pathway with a lower activation energy. This is the amount of energy needed by the substrate to become just unstable enough for a reaction to occur and for products to be formed. Enzymes speed up chemical reactions because they reduce the stability of bonds.
• The active site has a specific shape created by the tertiary structure of the protein molecule. This means that each enzyme can bind to only one type of substrate molecule.

  This is explained by the lock and key hypothesis. In an alternative hypothesis, the binding site changes shape to fit more closely around the substrate molecule. This is called the induced fit hypothesis.
• There are three main factors which can affect enzyme action: Temperature, pH and concentration
• Optimum – The best pH or temperature for an enzyme
• Denature – When an enzyme’s active site changes shape and no longer binds the substrate
• A change in the tertiary structure causes the active site to change shape and so the enzyme will no longer work
• Up until 40°C how does temperature affect rate of reaction. Link your answer to collision theory -

  • Increasing temperature increases the rate of reaction as there is increased kinetic energy of particles so they will collide more often and successfully

  What happens after 40°C?

  • The bonds holding the protein vibrate more. The vibrations increase until the bonds strain and then break. Breaking these bonds results in a change to the tertiary structure and the enzyme is denatured

  
• The temperature coefficient (Q10) tells us how much rate increases as temperature increases by 10ºC

  Q10 = R1 / R2

  R1= Rate at temperature 1

  R2= Rate at temperature 10ºC higher
• Thermophile - Organisms adapted to live in very hot environments such as hot springs or deep sea hydrothermal vents.

  Their enzymes have more bonds in their tertiary structures and so are more stable and resistant to temperature rises.
• Psychrophile - Live in extremely cold environments i.e. deep ocean, polar regions

  Their enzymes have more flexible structure in the active site.
• All proteins are affected by changes in pH. This is due to bonding (a change in pH actually refers to a change in hydrogen ion concentration)

  Hydrogen ions interact with the polar R groups. These interactions (an the interactions of R groups with themselves)are altered by changes in H+ concentration.

  •The more H+ (low pH), the less R groups can interact with each other.

  •The less H+ (high pH), there are less hydrogen bonds and interactions.

  
• If pH returns to the optimum a process called renaturation can occur in which the active site resumes shape. This is only if the pH change has been minimal
• •Amylase is an enzyme found in saliva. The pH in the mouth is around 6-7. Therefore this is the optimum in which amylase works. Amylase works to break down starch into maltose.
• •Pepsin is an enzyme in the stomach. This is an acidic environment with a pH of 2. Pepsin catalyses the break down of proteins into polypeptides.
• •Trypsin is an enzyme in the small intestine. It catalyses the break down of proteins into polypeptides. The pH here is around 7-8.
• Another factor which can affect enzyme action is concentration. Increasing substrate concentration will increase enzyme reaction rate BUT this is limited by the availability of active sites/enzymes.