Factors affecting enzyme activity (d)

Question 1

General trend for temperature

Answer 1

• increasing temperature increases the kinetic energy of the particles
• the particles move faster and collide more frequently
• thus more frequent (successful) collisions between enzyme and substrate molecules = increases rate of reaction

Question 2

Temperature coefficient

Answer 2

• a measure of how much a rate of reaction increases with a 10°C rise in temperature
• e.g. if Q₁₀=2, rate of reaction doubles with a 10°C temperature increase for enzyme-controlled reactions
• Q₁₀= R₂/R₁
• Where R₂ is the rate at the higher temperature and R₁ is the rate at the lower temperature.

Question 3

Denaturation

Answer 3

• at higher temperatures the bonds holding the protein together vibrate more + increases in vibrations strain the bond - they then break
• this changes the precise tertiary structure of the protein - changing its shape - becoming denatured
• changes the active site so it is no longer complementary to the substrate - it no longer fits so enzyme loses its function as a catalyst

Question 4

Optimum temperature

Answer 4

• optimum = the temperature at which the enzyme has the highest rate of activity - can vary
• once denatured above the optimum, decrease in rate of reaction is rapid
• at this point, the temperature coefficient no longer applies

Question 5

Temperature extremes

Answer 5

• enzymes adapted to the cold tend to have more flexible structures - particularly at the active site, so smaller temperature changes will denature them
• enzyme present in thermophiles are more stable due to increased number of bonds (H bonds + sulfur bridges) so more resistant to change as temp. rises.

Question 6

pH

Answer 6

• pH changes H⁺ ion concentration - acidic = more H⁺ ions, alkaline = less H⁺ ions
• H⁺ ions interact with polar and charged R-groups, thus changing its concentration changes the degree of interactions and affects the interaction of R-groups with each other
• increase in H⁺ ions = decrease in pH = less R-groups able to interact with each other - leading to bonds breaking and enzyme shape changing (and vice versa)
• enzyme only functions within a narrow pH range

Question 7

Optimum pH, renaturation + denaturation

Answer 7

• optimum pH - active site will be in right shape at certain hydrogen ion concentration
• renaturation: when pH changes from the optimum, the structure of the active site alters; if it returns to optimum, then the protein will resume its normal shape and catalyse the reaction again
• structure is irreversible when pH changes more significantly = denatures = decreases rate

Question 8

Substrate concentration

Answer 8

• increasing substrate concentrate increases number of substrate particles in a volume = higher collision rate = more enzyme-substrate complexes formed = increased rate of reaction
• Vₘₐₓ = the maximum initial velocity or rate of the enzyme-catalysed reaction. rate increases upto its Vₘₐₓ.
• at the Vₘₐₓ all active sites are occupied by substrate particles and no more enzyme-susbtrate complexes can be formed until products are released from the active site
• only way to increase the rate is to increase the temperature or add more enzyme - limiting factors etc

Question 9

Enzyme concentration

Answer 9

• increasing enzyme concentration increases available number of active sites in a volume - leading to the formation of enzyme-substrate complexes at a faster rate
• more active sites are available so rate increases to a higher Vₘₐₓ, until substrate concentration is the limiting factor again.

Question 10

Practicals to measure rate of enzyme activity

Answer 10

1. how fast the product appears - e.g. collecting oxygen from catalase catalysing the breakdown of hydrogen peroxide in a gas syringe or upturned measuring cylinder
2. measure the disappearance of substrate - e.g. amylase catalyses starch into maltose, so starch can be detected using iodine solution (KI and I); time how long it takes for starch to disappear using a spotting tile. alter the conditions.

Question 11

Practical for the effect of temperature on enzyme activity

Answer 11

1. set up boiling tubes with same volume + concentration of hydrogen peroxide
2. set up apparatus to measure the volume of oxygen produced
3. put each in a different temperature water baths. put a boiling tube of catalase in each temperature water bath and wait 5 minutes
4. pipette the same volume of oxygen produced into each boiling tube
5. record volume of oxygen produced in the first 60 seconds
6. repeat at each temperature 3 time and calculate the mean
7. calculate the rate of reaction at each temp and compare
   Different factors can be experimented: for this, pH should be constant by using a buffer solution

Question 12

Serial dilutions

Answer 12

Change concentrations of water and the enzyme to produce the desired concentration of the enzyme