2.4.4 the effect of temp of enzyme activity

Question 1

what happens if a substance is heated

Answer 1

• extra energy (from heat) causes molecules to move faster
• increases rate of collisions between molecules
• increases force they collide with

Question 2

what happens if the reactant mixture (containing enzyme/substrate molecules) is heated

Answer 2

• both molecules gain kinetic energy & move faster
• increase rate of successful collisions (number per second)
• rate of formation of ES complex & rate of reaction increases which increases number of enzyme-product complexes per second (to a point)
• at enzymes optimum temp, rate of reaction is maximum

Question 3

what effect does the heat, causing the molecules to vibrate, have on the molecules

Answer 3

• break some weak bonds (eg. hydrogen/ionic) that hold tertiary structure of enzymes active site
• as it changes, substrate molecules don’t fit & rate of reaction decreases
• more heat = shape of active site irreversibly changes - no longer complementary to substrate
• reaction stops
• enzyme = denatured

Question 4

what is the optimum temperature

Answer 4

temperature at which enzyme works best & at maximum rate of reaction

Question 5

example of enzyme that works best at cool (really low) temperatures

Answer 5

psychrophilic bacteria

Question 6

example of enzyme that lives in very hot conditions (hot springs) and how

Answer 6

thermophilic bacteria
- enzymes/their other proteins are heat stable
- have more disulfide bonds that don’t break with heat & keep shape of protein molecules stable
- high optimum temperatures

Question 7

what’s the temperature coefficient Q10

Answer 7

refers to the increase in the rate of a process when the temperature is increased by 10 degrees

Question 8

equation for temperature coefficient Q10

Answer 8

rate of reaction at (T + 10) degrees ÷ rate of reaction at (T)degrees

Question 9

what is Q10 (approximately) for chemical reactions in a test tube
- what does this mean

Answer 9

2
- it means that for every 10 degrees rise in temp the rate of reaction is doubled

Question 10

what is Q10 for metabolic reactions catalysed by enzymes
- because…

Answer 10

• between 0 degrees & approx 40 degrees, the rate of reaction is roughly doubled for every 10 degrees rise
  –> as increase in temp. provides more kinetic energy, so enzyme & substrate molecules move faster/collide more

Question 11

what is Q10 for enzymes above their optimum temp
- because…

Answer 11

• value of temp. coefficient drops
  –> as higher temps. alter structure of the active sites of the enzyme molecules so they’re no longer complementary to shape of substrate molecules