Unit 1, everything.

• The effect of increased temperature on enzymes is summarised in the diagram.
• Enzymes are globular proteins with a tertiary structure that are synthesised by living cells and can act inside the cell (intercellular enzymes) or can be secreted by cells (extracellular enzymes).
• The 3D shape of an enzyme molecule creates an active site – a 3D space in the molecule into which specific substrate molecule(s) can fit and bind.
• The active site of an enzyme has a specific shape, which is determined by the sequence of amino acids in the polypeptide; if the sequence of amino acids changes then the active site will change shape and the substrate will not bind to the active site because they are no longer complementary.
• Enzymes work as follows: When a substrate and an enzyme collide successfully, the substrate fits into and binds to the active site by interactions with R groups/polar atoms of the amino acids that make up the active site to form an enzyme-substrate complex.
• The ability of the R groups and the substrate to form bonds is affected by temperature and pH.
• Bonds in the substrate are distorted, which puts strain on the bonds that are going to be broken and increase the chance that they will break.
• Breaking the bonds brings new atoms in the substrates closer together and new bonds can form.
• While energy is needed to break the existing bonds, energy is released when the new bonds are made.
• The energy needed for the reaction to take place is called the activation energy for that reaction.
• When an enzyme-substrate reaction forms, the activation energy needed for the reaction to take place is reduced – the reaction takes place faster - the enzyme acts as a biological catalyst.
• Each enzyme is specific to a particular substrate – so even if three substrates undergo the same reaction, there has to be three different enzymes to carry out this same function.
• One theory of how enzymes work is that the active site in the enzyme is like a lock into which only one substrate molecule can fit like a key.
• The substrate must be complementary to the active site of the enzyme so that it can bind to it.
• The active site is a fixed shape so a substrate has to collide in the correct orientation with the active site in order that bonds can form and produce an enzyme-substrate complex.
• While the substrate binds to the enzyme chemical changes can take place and the substrate molecules are either digested (broken down) or combined to form new products.
• As temperature increases particles gain kinetic energy.
• Bonds in the enzyme begin to vibrate and eventually they break – weak hydrogen bonds are broken first.
• A substrate molecule forms an enzyme-substrate complex by bonding to amino acid side groups in the active site of an enzyme.
• The enzyme is now fully denatured.
• Eventually, there is a loss of secondary and tertiary structure, the 3D shape of the active site changes and the active site can no longer form bonds with the substrate.
• Up to the optimum temperature for an enzyme, bonds remain intact and can form enzyme-substrate complexes as there is no change to the active site.
• Any change to the charges due to a change in the pH would reduce the ability of the substrate to bind to the side groups of the amino acids lining the active site.
• Below the optimum temperature, as the temperature increases, the enzymes and substrates have more kinetic energy so there are more successful collisions and therefore more enzyme-substrate complexes are formed and the rate of reaction increases.
• Catabolism is a process where many enzymes, such as digestive enzymes, are involved in breaking down complex substrate molecules into two or more product molecules.
• The change in charge on some side groups changes the ability of the enzyme’s active site to form bonds with a substrate – if bonds are not formed then the enzyme may not be able to lower the activation energy and the enzyme is inactivated/denatured.
• The induced fit theory is another theory of how enzymes work, where as the substrate molecule enters the active site, forces of attraction between the substrate and the R groups/polar atoms of the amino acids in the active site are formed, causing the shape of the active site to change and stronger bonds are then formed with the substrate.
• Changes in the pH of a solution can cause changes to the bonding between amino acids and, therefore, cause changes to the secondary and tertiary structure of a protein.
• Small changes in pH cause small reversible changes in enzyme structure – inactivation; but large changes can permanently change the structure of the protein – denaturation.
• As temperature increases above the optimum, the increased heat gives more energy to particles.
• Anabolism is a process where two substrate molecules are combined to form a single product molecule.