🤒Factors affecting enzyme activity 🤒

• An increase in temperature means an increase in kinetic energy of the particles which results in more frequent successful collisions between substrate and enzyme because the particles will be moving faster and colliding more frequently. This leads to an increased rate of reaction
• The temperature coefficient -Q10- of a reaction is a measure of how much faster the rate of reaction increases with a 10 degree C rise in temperature.

  For enzyme-controlled reactions this is usually taken as 2: the rate of reaction doubles with a 10 degrees C increase in temp
• At higher temperatures, the bonds holding the protein (enzyme) together vibrate more. As temperature increases, vibrations increase causing the bonds to strain and eventually break.

  The breaking of these bonds changes the precise tertiary structure of the protein. This means the enzyme changes shape causing it become denatured because the active site shape changes so it is no longer complementary to its substrate.

  The substrate no longer fits in the active site so the enzyme will no longer function as a catalyst
• The optimum temperature is the temperature at which the enzyme has the highest rate of activity
• Once enzymes have denatured above optimum temp, the decrease in the rate of reaction is rapid as it happens to all of the enzymes ate the same temp so the loss of activity is relatively abrupt
• The temperature coefficient, Q10, doesn't apply once enzymes have denatured
• The decrease in rate of reaction below optimum temp is less rapid because the enzymes don't denature they are just less active
• Enzymes that are adapted to the cold tend to have more flexible structures, particularly at the active site, making them less stable than enzymes that work at higher temps. This means that smaller temp changes will denature them
• Thermophiles are organisms that are adapted to living in very hot environments (e.g. hot springs, deep sea hydrothermal vents). Their enzymes are more stable than others because of an increased number of bonds, particularly hydrogen bonds and sulfur bridges, in their tertiary structures. The shapes of these enzymes are more resistant to change as temp rises
• Hydrogen bonds and ionic bonds between polar and charged amino acid R-groups are what hold proteins in their precise 3D shape
• A change in pH is a change in hydrogen ion concentration:

  • there are more H+ ions in a low pH environment
  • there are fewer H+ ions in a high pH environment
• The active site will only be the right shape at a certain hydrogen ion concentration. This is the optimum pH.
• If the pH changes from the enzyme's optimum, the structure of the enzyme and its active site is altered. However, if pH returns to the optimum pH, the protein will resume its normal shape and catalyse its reaction again. This is called renaturation. When pH changes more significantly (beyond a certain pH), the enzyme will be irreversibly altered so it will denature
• H+ ions interact with polar and charged R-groups. Changing the concentration of H+ ions changes the degree of this interaction. The interaction of R-groups with hydrogen ions also affects the interaction of R-groups with each other. If there are more H+ ions (low pH), the R-groups will interact less with each other so the bonds will break and the enzyme's shape will change. If there are less H+ ions (high pH), the reverse is true. Enzymes only function within a narrow pH range because its shape changes if pH changes
• If the concentration of the substrate is increased, the number of substrate particles increases so there will be a higher collision rate with enzyme active sites. This increases the formation of enzyme-substrate complexes so the rate of reaction increases.
• When the concentration of the enzyme increases, the number of available active sites increases so enzyme-substrate complexes form at a faster rate. This results in an increased rate of reaction
• Rate of reaction increases up to its maximum (Vmax) when all the active sites are occupied by substrate molecules so no more enzyme-substrate complexes can be formed until the products are released from the active sites. At this point the only way to increase the rate of reaction is to add more enzyme or increase temp.
• When the concentration of the enzyme is increased, more active sites are available so the reaction rate can reach a higher Vmax. The substrate concentration then becomes a limiting factor so increasing it will allow the reaction rate to rise again until the new Vmax is reached. When the new Vmax is reached, enzyme concentration (now limiting) is increased again to increase Vmax again and the cycle repeats.