Factors affecting enzyme activity Flashcards
Does a rise in temperature affect enzyme activity?
Yes - the rate of an enzyme-controlled reaction increases when the temperature increases, but only to a point, as if teh temperature is too high the enzyme is denatured and the rate of reaction then falls
Why does increased temperature affect the rate of enzyme-controlled reactions?
Because increased heat means increased kinetic energy, so enzyme and substrate molecules are moving around faster meaning they’re more likely to collide, and they’re also moving around with more energy so the collisions are more likely to be successful and result in a reaction.
(Remember: if the temperature gets too high the reaction stops)
Why do enzyme-controlled reactions stop if the temperature gets too high?
Increased temperatures makes enzyme molecules vibrate more, which is good to a point, but past this point the vibrations increase to a level that they cause the enzyme molecule to change shape as some of the bonds on the structure are broken. This changed shape means that the substrate can no longer fir in teh active site of the enzyme, so the enzyme is no longer able to catalyse the reaction. The enzyme is now denatured - it can no longer function as a catalyst.
What does the temperature coefficient (Q10) show?
It shows how rate changes with temperature. In enzyme controlled reactions, the Q10 value is usually around 2.
The Q10 value for a reaction shows how much the rate changes when the temperature is increased by 10 degrees. So, at temperatures before the optimum, if a reaction has a Q10 of 2 it means that the rate doubles when the temp is increased by 10 degrees, or if a reaction has a Q10 of 3 it means the rate triples when the rate is increased by 10 degrees.
What pH do human enzymes usually function best at? Name an exception.
All enzymes have an optimum pH value - in humans its usually about pH 7 (neutral), but there are exceptions.
Pepsin is an exception - it functions best at pH 2, which is good because its found in teh stomach which is an acidic environment.
Why does a pH higher or lower than the optimum pH for an enzyme-controlled reaction affect the rate?
At a higher pH than the optimum (a more alkaline environment), the OH- ions found in alkalis can affect the ionic bonds and hydrogen bonds that hold the enzymes tertiary structure in place, so the enzymes active site shape is changed, so the substrate no longer fits, so the enzyme is denatured.
At a lower pH than the optimum (a more acidic environment), the H+ ions found in acids can affect the ionic bonds and hydrogen bonds that hold the enzymes tertiary structure in place, so the enzymes active site shape is changed, so the substrate no longer fits, so the enzyme is denatured.
How does enzyme concentration affect the rate of an enzyme-controlled reaction?
The higher the concentration of enzyme, the more likely a substrate molecule is to collide with one and form an enzyme-substrate complex, so the faster the rate.
However, it will not increase the rate indefinitely - if the amount of substrate is not also increasing, then you reach a point where there’s plenty of enzyme molecules to deal with the available substrate, so adding more enzyme will not have any further affect until more substrate is added.
How does substrate concentration affect the rate of an enzyme-controlled reaction?
The higher the substrate concentration, the faster the reaction, because a collision between substrate and enzyme is more likely. But this is only true until all of the enzymes have as much substrate as they can cope with and all teh active sites are full - at this point more enzyme needs to be added if the rate were to increase any more.
As the reaction progresses, substrate gets ‘used up’ (remember enzyme does not!), so substrate concentration decreases over time (unless more substrate is added during the reaction). So, if no other variables are changed, the rate of reaction will decrease over time, making the initial rate of reaction the highest.
Name 4 things that can affect the rate of an enzyme-controlled reaction.
pH, temperature, enzyme concentration, substrate concentration
One way to measure the rate of an enzyme-controlled reaction is to measure how fast the produce of the reaction appears. Give an example of this (hint: what does the catalase enzyme do?)
Catalase enzyme catalyses hydrogen peroxide breakdown to water and oxygen, so you can collect the oxygen produced and measure how fast its given off.
One way to measure the rate of an enzyme-controlled reaction is to measure the disappearance of the substrate. Give an example of this (hint: what does the amylase enzyme do?)
Amylase enzyme catalyses the breakdown of starch to maltose, so you can measure how quickly to starch is being used up by adding drops of the starch solution to a spotting tile with a solution of potassium iodide and iodine in each well (which turns black-blue in the presence of starch). When you stop getting a colour change, all the starch has been broken down and the reaction is compete.
