2.4.4-2.4.5-2.4.6(Factors affecting rates of enzyme activity)

State the 3 factors which affect the rate of enzyme activity

• Temperature

• pH

• Substrate and enzyme Concentration

Describe and explain how increasing temperature affects the rate of enzyme action

• As you increase the temperature, the rate of reaction increases

• This is because as you increase the temperature, the kinetic energy of the substrate and enzymes increases which causes more successful collisions

• This leads to the formation of more enzyme substrate complexes which leads to more enzyme-product complexes per second which leads to more product is formed

• This happens up to the optimum temperature of the enzymes activity where the rate of reaction is at its maximum

• After this point, the temperature is too high and hydrogen and ionic bonds begin to break

• This cause the active site tertiary structure to change, which leads to the active site no longer being complementary to the substrate and less ESCs form which means less product is formed

• This leads to a decreased rate of reaction

• As more heat is applied, the enzymes begin to denature and the rate of reaction eventually reaches 0

What is the temperature coefficient equation

Q10 = Rate of reaction at (T+10) C / Rate of reaction at T C

For most enzyme controlled reactions, what is the temperature coefficient

• 2

State what is meant by a buffer

• A buffer is something which stops the changes in pH in a solution to maintain a desired pH

Describe and explain how pH can affect the rate of reaction of enzymes

• H+ ions or OH- ions are what affect pH.

• These H+ and OH- ions disrupt hydrogen and ionic bonds in the enzyme

• This leads to the tertiary structure of the enzyme’s active site to deform

• This leads to the active site no longer being complementary to the substrate

• This leads to less ESCs forming, leading to less product being formed which leads to a decreased rate of reaction when not at an optimum pH

• Increasing H+ ions will also affect with the binding of the substrate molecule to the active site which will further decrease rate of reaction

Describe how enzymes are adapted to working in different parts of the body

• Enzymes that work extracullarly have an optimum pH different from 7

  • For example, amylase works best at 6.8 pH

• Enzymes in the stomach work at a very low pH due to the acidic conditions in the stomach:

  • For example, pepsin works best pHs 1-2

• Enzymes in the small intestine work best at pHs of 7.8. This pH is caused by bile made in the liver neutralising the pH

  • For example, this is trypsin’s optimum pH

Describe and explain the effect of changing substrate concentration of the rate of reaction

• As you increase the concentration of substrates, the rate of reaction increases

• This is because more successful collisions occur

• This causes more ESCs to form which leads to more product forming

• Substrate concentration is the limiting factor, because, as it increases, the rate of reaction also increases

• As the concentration of substrate further increases, the reaction will reach its maximum rate of reaction, which will not change as you add more substrate

• This is because all the enzymes active sites are occupied with substrate molecule and therefore the maximum number of ESCs are formed and no more successful collisions can occur and the maximum number of products are being formed

• At this point, enzymes are the limiting factor

Describe and explain the effect of changing enzyme concentration of the rate of reaction

• As you increase the concentration of enzymes, you increase the number of free active sites

• Initially, enzyme concentration is the limiting factor

• This causes more successful collisions and therefore increasing the formation of ESCs complexes

• This causes more product to form and therefore increasing rate of reaction

• As the enzyme concentration further increases, the reaction will reach its maximum rate of reaction and the rate will not change as you add more enzymes

• This is because there are not enough substrates to occupy all the available active sites of the enzymes

• This now means that the substrate concentration is the limiting factor