Chapter 3.2

Question 1

Rate: Temperature

Answer 1

• Lower temperatures

- Higher temperatures

Question 2

Lower temperatures

Answer 2

either prevent reactions from proceeding or slow them down:

• Molecules move relatively slowly
• Lower frequency of successful collisions between substrate molecules and active site of enzyme
• Less frequent enzyme-substrate complex formation
• Substrate and enzyme collide with less energy, making it less likely for bonds to be formed or broken (stopping the reaction from occurring)

Question 3

Higher temperatures speed up reactions

Answer 3

• Molecules move more quickly
• Higher frequency successful collisions between substrate molecules and active site of enzyme
• More frequent enzyme-substrate complex formation
• Substrate and enzyme collide with more energy, making it more likely for bonds to be formed or broken (allowing the reaction to occur)

Question 4

Denaturation due to an continuous increase in temperature

Answer 4

• Bonds (eg. hydrogen bonds) holding the enzyme molecule in its precise shape start to break
• This causes the tertiary structure of the protein (ie. the enzyme) to change
• This permanently damages the active site, preventing the substrate from binding
• Denaturation has occurred once the substrate can no longer bind
• Few human enzymes can function at temperatures in excess of 50o As humans maintain a body temperature of about 37oC, even temperatures above 40oC would begin to cause denaturation of the enzymes

Question 5

Rate: pH

Answer 5

• All enzymes have an optimum pH or a pH at which they operate best
• Enzymes are denatured at extremes of pH
• enzyme functions can be an indicator of its optimal environment

Question 6

Enzymes are denatured at extremes of pH

Answer 6

• Hydrogen and ionic bonds hold the tertiary structure of the protein (ie. the enzyme) together
• Below and above the optimum pH of an enzyme, solutions with an excess of H+ ions (acidic solutions) and OH– ions (alkaline solutions) can cause these bonds to break
• This alters the shape of the active site, which means enzyme-substrate complexes form less easily
• Eventually, enzyme-substrate complexes can no longer form at all
• At this point, complete denaturation of the enzyme has occurred

Question 7

Rate: Enzyme Concentration

Answer 7

Enzyme concentration affects the rate of reaction

• The higher the enzyme concentration in a reaction mixture, the greater the number of active sites available and the greater the likelihood of enzyme-substrate complex formation
• As long as there is sufficient substrate available, the initial rate of reaction increases linearly with enzyme concentration
• If the amount of substrate is limited, at a certain point any further increase in enzyme concentration will not increase the reaction rate as the amount of substrate becomes a limiting factor

Question 8

Rate: Substrate Concentration

Answer 8

• The greater the substrate concentration, the higher the rate of reaction
• For this reason, in the graph, there is a linear increase in reaction rate as substrate is added, which then plateaus when all active sites become occupied

Question 9

The greater the substrate concentration, the higher the rate of reaction:

Answer 9

• As the number of substrate molecules increases, the likelihood of enzyme-substrate complex formation increases
• If the enzyme concentration remains fixed but the amount of substrate is increased past a certain point, however, all available active sites eventually become saturated and any further increase in substrate concentration will not increase the reaction rate
• When the active sites of the enzymes are all full, any substrate molecules that are added have nowhere to bind in order to form an enzyme-substrate complex

Question 10

Rate: Inhibitor Concentration

Answer 10

-There are two types of inhibitors: competitive and non-competitive
-Both types of inhibitors slow down or stop enzyme activity
-

Question 11

Increasing the concentration of an inhibitor

Answer 11

reduces the rate of reaction and eventually, if inhibitor concentration continues to be increased, the reaction will stop completely

Question 12

competitive inhibitors

Answer 12

countering the increase in inhibitor concentration by increasing the substrate concentration can increase the rate of reaction once more (more substrate molecules mean they are more likely to collide with enzymes and form enzyme-substrate complexes)

Question 13

non-competitive

Answer 13

increasing the substrate concentration cannot increase the rate of reaction once more, as the shape of the active site of the enzyme remains changed and enzyme-substrate complexes are still unable to form

Question 14

Michaelis-Menten enzyme kinetics

Answer 14

is used to investigate the kinetics of enzyme catalysed reactions (enzyme kinetics is an area in biochemistry that studies how different variables affect reaction rates)

• The rate of reaction is measured at different substrate concentrations
• The two important values deduced are the Vmax (maximum rate of reaction at saturating substrate concentrations) and the Km, which is the substrate concentration at ½Vmax (also known as the Michaelis-Menten constant)

Question 15

The two important values deduced are the Vmax (maximum rate of reaction at saturating substrate concentrations) and the Km, which is the substrate concentration at ½Vmax (also known as the Michaelis-Menten constant)

Answer 15

• The Michaelis-Menten constant is the substrate concentration at which the enzyme works at half its maximum rate
• At this point, half of the active sites of the enzyme are occupied by substrate molecules
• The higher the affinity of the enzyme for the substrate, the lower the substrate concentration needed for this to occur
• This is why the Michaelis-Menten constant is a measure of the affinity of an enzyme for its substrate

Question 16

there is an inverse relationship

Answer 16

• between the Km and the affinity of an enzyme for its substrate
• An enzyme with a high Km has a low affinity for its substrate and an enzyme with a low Km has a high affinity for its substrate

Question 17

Enzyme reversed Inhibitors

Answer 17

An enzyme’s activity can be reduced or stopped, temporarily, by a reversible inhibitor
There are two types of reversible inhibitors:
Competitive inhibitors have a similar shape to that of the substrate molecules and therefore compete with the substrate for the active site
Non-competitive inhibitors bind to the enzyme at an alternative site, which alters the shape of the active site and therefore prevents the substrate from binding to it

Question 18

Reversible inhibitors can act as

Answer 18

regulators in metabolic pathways

• Metabolic reactions must be very tightly controlled and balanced, so that no single enzyme can ‘run wild’ and continuously and uncontrollably generate more and more of a particular product
• Metabolic reactions can be controlled by using the end-product of a particular sequence of metabolic reactions as a non-competitive, reversible inhibitor

Question 19

process is known as end-product inhibition

Answer 19

• As the enzyme converts substrate to product, the process is itself slowed down as the end-product of the reaction chain binds to an alternative site on the original enzyme, changing the shape of the active site and preventing the formation of further enzyme-substrate complexes
• The end-product can then detach from the enzyme and be used elsewhere, allowing the active site to reform and the enzyme to return to an active state
• This means that as product levels fall, the enzyme begins catalysing the reaction once again, in a continuous feedback loop

Question 20

Enzyme Activity: Immobilised Vs. Free

Answer 20

• Enzymes can be added to solutions and are thereby considered ‘free’ or they can be immobilised
• Immobilised enzymes are enzymes that have been bound to an inert, stationary and insoluble material such as alginate
• The substrate is then passed over the immobilised enzyme and the product is collected

Question 21

immobilised advantages

Answer 21

• There is no enzyme in the product (the product is uncontaminated) and therefore there is no need to further process or filter the end product
• The immobilised enzyme can be reused multiple times which is both efficient and cost-effective (enzymes are expensive)
• Immobilised enzymes have a greater tolerance of temperature and pH changes (immobilisation often makes enzymes more stable)

Question 22

production of lactose-free milk

Answer 22

• The enzyme lactase can be immobilised using alginate beads
• Milk is run through the column of lactase-containing beads
• The lactase hydrolyses the lactose in the milk to glucose and galactose
• This ensures the milk is lactose-free
• It can also then be used to make other lactose-free dairy products