My AP Biology ThoughtsUnit 1 Episode #46

Welcome to My AP Biology Thoughts podcast, my name is Nidhi and I am your host for episode 46 called Unit 1 The Impact of Temperature and pH on enzymes. Today we will be discussing what an enzyme is and how the pH and temperature of the environment affects the enzyme and its substrate.

Segment 1: Introduction to The Impact of Temperature and pH on enzymes

An enzyme is a protein or a RNA molecule that acts as a catalyst in chemical reactions, helping to reduce the activation energy needed for the reaction to occur. Often, this speeds up the rate of reaction. Enzymes are not changed or consumed by the reactions they catalyse and as a result can be reused. Enzymes are typically named after the molecules they react with, which is called the substrate, and they end with the suffix ‘-ase’. The active site is the region on the surface of the enzyme which binds to the substrate molecule. The active site and the substrate complement each other in terms of both shape and chemical properties. Enzymes are selective and each enzyme only speeds up a specific reaction. pH is a scale from 1-14 used to specify how acidic or how basic a solution is. A number lower than the neutral 7 is considered an acid while a number higher than 7 is a base. With enzymes, changes in pH can affect active sites by changing its shape or charge and making it harder for substrates to bind. Small changes in pH above or below the Optimum for the enzyme do not cause a permanent change to the enzyme, since the bonds can be reformed. However, extreme changes in pH can cause enzymes to Denature and permanently lose their function. The optimum pH, or the pH where the enzyme is most active, depends on where it normally works. For example, enzymes in the small intestine have an optimum pH of about 7.5, but stomach enzymes have an optimum pH of about 2. Low temperatures result in insufficient thermal energy for the activation of a reaction to proceed. Increasing the temperature will increase the speed and motion of both enzyme and substrate, resulting in higher enzyme activity since a higher kinetic energy will result in more frequent collisions between the enzymes and substrates. At an optimal temperature for the enzyme, the rate of activity will be at its peak. Higher temperatures will cause enzyme stability to decrease, because the thermal energy disrupts the enzyme’s hydrogen bonds. This causes the enzyme’s active site to lose its shape, resulting in denaturation. 

Segment 2: Example of The Impact of Temperature and pH on enzymes

Trypsin and pepsin are both enzymes in the digestive system which break protein chains in food into smaller peptide chains or into individual amino acids. Pepsin works in the highly acidic conditions of the stomach. It has an optimum pH of about 1.5. On the other hand, trypsin works in the small intestine, parts of which have a pH of around 7.5. If at a pH of around 7, a substrate attaches itself to the enzyme via two ionic bonds, then a change in pH can definitely make it difficult for the substrate to bond to the enzyme. In an example enzyme, the groups allowing ionic bonding are caused by the transfer of a hydrogen ion from a COOH group in the side chain of one amino acid to an -NH2 group in the side chain of another. At a lower pH, the -COO- will pick up a hydrogen ion and with this an ionic bond can no longer form between the substrate and the enzyme. If those bonds were necessary to attach the substrate and activate it, then at this lower pH, the enzyme won't work. With a pH higher than 7, the NH3+ will lose a hydrogen ion and again an ionic bond can’t...