2. Factors Affecting Enzyme Activity Flashcards
What 4 factors affect enzyme activity
- Temperature
- pH
- Enzyme Concentration
- Substrate Concentration
How does temperature affect enzyme activity
- As temp increases, the rate of enzyme activity increases.
- Increased heat mans more kinetic energy, so molecules move faster. This makes the enzymes more likely to collide with the substrate molecules.
- The energy of these collisions also increases, which means each collision is more likely to result in a reaction.
- HOWEVER, once optimum temperature is achieved, the vibration of the enzymes molecules **breaks* some of the bonds that hold the enzyme in shape. The active site changes shape & the enzyme & substrate no longer fit tg - the enzyme is denatured
see pg44 for graph on temperature effect on enzyme activity
What is the optimum temperature for human enzymes
37
What is the temperature coefficient (Q10)
Temperature coefficient or Q10 value for a reaction shows how much the rate of a reaction changes when the temp is raised by 10dc.
What is the equation for temperature coefficient (Q10)
Q10 = R2 (rate at higher temperature) / R1 (rate at lower temperature)
see pg44 for eg of calculating Q10
What do certain Q10 values mean
- At temps before the optimum, a Q10 value of 2 means that the rate doubles when the temp is raised by 10dc.
- A Q10 value of 3 would mean that the rate trebles.
- Most enzyme-controlled reactions have a Q10 value of around 2.
How does pH affect enzyme activity
- All enzymes have an optimum pH value.
- Most human enzymes work best at pH 7 (neutral), but there are exceptions. Pepsin for eg, works best at acidic pH 2, which is useful bc it’s found in the stomach.
- Above & below the optimum pH, the H+ & OH- ions found in acids & alkalis can mess up the ionic bonds & hydrogen bonds that holds the enzyme’s tertiary structure in place.
This makes the active site change shape, so the enzyme is denatured
see graph of pH effect on enzyme activity on pg44
How does Enzyme concentration affect enzyme activity
- The more enzyme molecules there are in a solution, the more likely a substrate molecule is to collide with one & form an enzyme-substrate complex.
- So, increasing the concentration of the enzyme increases the rate of reaction
- BUT, if the amount of substrate is limited, there comes a point when theres more than enough enzyme molecules to deal with all the available substrate, so adding more enzyme has no further effect.
see pg45 for graph on enzyme concentration effect on enzyme activity
How does Substrate concentration affect enzyme activity
- The higher the substrate concentration, the faster the reaction - more substrate molecules means a collision between substrate & enzyme is more likely & so more active sites will be used.
- HOWEVER, this is only true up until a ‘saturation’ point. After that, there are so many substrate molecules that the enzymes have abt as much as they can cope with (all active sites are full), & adding more substrate **makes no difference* to rate of reaction.
- Substrate concentration decreases with time during a reaction (unless more substrate is added to the reaction mixture), so if no other variables are changed, the rate of reaction will decrease overtime too.
- This makes the initial rate of reaction the highest rate of reaction.
see pg45 for graph of substrate concentration effect on enzyme activity
2 ways of measuring the rate of an enzyme-controlled reaction: Example 1
- Measure how fast the product of the reaction appears. We can measure this with the enzyme catalase.
- Catalase catalyses the breakdown of hydrogen peroxide into water & oxygen.
- Its easy to collect the oxygen produced & measure how fast its given off.
2 ways of measuring the rate of an enzyme-controlled reaction: Example 2
- Measure the disappearance of the substrate rather than the appearance of the product & use this to compare the rate of reaction under diff conditions.
FOR EG.
The enzyme amylase catalyses the breakdown of starch to maltose. It’s easy to detect starch using a solution of potassium iodine & iodine.
You can time how long it takes for the starch to disappear by regularly sampling the starch solution. You can then alter the conditions & compare rates.
see pg45 for diagrams of both eg1 & 2 practical
Investigating the effect of temperature on catalase activity: Method
- Set up boiling tubes containing same vol & concentration of hydrogen peroxide. To keep pH constant, add equal volumes of a buffer solution to each tube.
- Set up apparatus to measure volume of oxygen produced from each boiling tube. (Use a delivery tube & upside down measuring cylinder).
- Put each boiling tube in water bath set to diff temps (10, 20, 30, etc) for 5mins along w another tube containing catalase.
- Use pipette to add the same volume & concentration of catalase to each boiling tube.
- RECORD how much oxygen is produced in first 60secs of the reaction. Use a stopwatch measure time.
- REPEAT at each temp three times, & use results to find the mean vol of oxygen produced at each temp.
- CALCULATE the mean rate of reaction at each temp by dividing the volume of oxygen produced by time taken.
(unit for rate of reaction will be cm^3/s^-1)
What is the purpose of a buffer solution
A buffer solution is able to resist changes in pH when small amounts of acid or alkali are added
Investigating the effect of temperature on catalase activity: Independent variable
Temperate is the independent variable
Investigating the effect of temperature on catalase activity: Dependent variable
The volume of oxygen produced
Investigating the effect of temperature on catalase activity: Control variable
Must control all other variables that could affect the outcome of the investigation. This includes pH, enzyme concent, substrate concent.
Investigating the effect of temperature on catalase activity: How would you alter this to investigate effect of substrate concentration
Keep the temp of the reaction the same, but prepare boiling tubes w different concentrations of hydrogen peroxide (this could be done using **serial dilutions).
Investigating the effect of temperature on catalase activity: How would you alter this to investigate effect of pH
Could add a buffer solution w a different pH to each tube
