Topic 3 Enzymes.

Question 1

What is a catalyst?

Answer 1

A catalyst is a substance that speeds up or increases the rate of a chemical reaction but remains unchanged by the reaction at the end of the reaction.

Question 2

What is an enzyme?

Answer 2

An enzyme is a globular protein that functions as a biological catalyst.

Question 3

What is a globular protein?

Answer 3

A globular protein is a type of spherical shaped protein.

They are generally water soluble and typically have metabolic roles.

Question 4

What kind of a protein structure does an enzyme have?

Answer 4

Enzymes have a tertiary protein structure with hydrophilic R groups externally and hydrophobic R groups internally.

Question 5

What is a tertiary structure?

Answer 5

The coiling of a protein into its function 3D shape, held together by external hydrophilic interactions, internal hydrophobic interactions, ionic bond interactions and disulphide bonds.

Question 6

What is the difference between a hydrophobic and hydrophilic molecule?

Answer 6

A hydrophilic molecule is one that is able to interact with water.
A hydrophobic molecule is one that is not able to interact with water.

Question 7

What are the two types of enzymes?

Answer 7

Intracellular and extracellular enzymes.

Question 8

What is the difference between an intracellular enzyme and an extracellular enzyme?

Give an example of an intracellular and an extracellular enzyme.

Answer 8

An intracellular enzyme is an enzyme that acts within cells e.g. catalase and DNA polymerase.

An extracellular enzyme is an enzyme that is secreted by cells and functions outside of cells e.g. enzymes used in digestion such as amylase.

Question 9

How do enzymes speed up the rate of reaction?

Answer 9

Enzymes speed up the rate of reaction by lowering the activation energy, which is the minimum amount of energy required for a reaction to take place.

Question 10

What is the active site?

Answer 10

A specific region of an enzyme where the substrate binds and the reaction takes place.

Question 11

Describe enzyme specificity.

Answer 11

Each enzyme has a specific active site shape that must be complementary to the substrate, meaning that only one type of substrate fits into the active site of each enzyme to form an enzyme-substrate complex.

Question 12

What are the two hypotheses for enzyme action?

Answer 12

The lock-and-key hypothesis and the induced-fit hypothesis.

Question 13

What is the lock-and-key hypothesis?

Answer 13

The lock and key hypothesis states that the substrate fits perfectly into the active site of an enzyme.

Question 14

Explain enzyme action with reference to the lock-and-key hypothesis.

Answer 14

• An enzyme (lock) has a cleft in its surface called the active site to which the substrate molecule (key) has a complementary shape to.
• Random movement of the enzyme and substrate brings the substrate into the active site. This forms the enzyme-substrate complex.
• The reaction then occurs, converting the substrate into products and forming an enzyme-products complex. The products then leave the active site, leaving the enzyme molecule unchanged and ready to bind with another of the same type of substrate molecule.

Question 15

What holds the substrate in place once it has entered the active site of the enzyme forming the enzyme substrate complex?

Answer 15

The substrate is held in place by temporary bonds which form between the substrate and some of the R groups of the enzymes amino acids.

Question 16

What is the induced-fit hypothesis?

Answer 16

The induced fit hypothesis proposes that as the substrate interacts with the R groups of the amino acids at the active site of the enzyme, the enzyme is able to change shape in order to create a stronger binding to the substrate.

Question 17

What are the factors that affect the rate of enzyme-controlled reactions?

Answer 17

• Temperature.
• pH.
• Enzyme concentration.
• Substrate concentration.
• Inhibitor concentration.

Question 18

Describe the effect on enzyme activity when the temperature is up to the enzyme’s optimum.

Answer 18

As temperature increases to the optimum, the kinetic energy of the enzyme and substrate increases, causing more collisions between the enzyme and substrate. This causes the formation of more enzyme-substrate complexes, leading to an increase in enzyme activity.

Question 19

Describe the effect on enzyme activity when the temperature is above the optimum.

Answer 19

At very high temperatures above the optimum, the enzymes become denatured and the active site changes shape. This decreases the rate of reaction as enzyme-substrate complexes cannot form.

Question 20

What is denaturation?

Answer 20

A permanent change in the shape of an enzyme’s active site that prevents the binding of a substrate.

Question 21

Describe the effect on enzyme activity when the temperature is below the optimum.

Answer 21

At low temperatures, enzyme activity is low because the enzyme and substrate molecules have less kinetic energy so there are fewer collisions between them.

Question 22

What causes an enzyme to denature?

Answer 22

At high temperatures or lower or higher than optimum pH the bonds in the enzymes tertiary structure break resulting in the shape of the active site changing.

Question 23

What is pH?

Answer 23

pH is a measure of the concentration of hydrogen ions in a solution.

Question 24

Describe the effect on enzyme activity when deviating from the optimum pH.

Answer 24

Deviating from the optimum pH (too high or too low) causes the enzyme’s active site to become denatured. Hence, it can no longer form enzyme-substrate complexes, leading to a decrease in enzyme activity.

Question 25

Describe the effect on enzyme activity when enzyme concentration increases.

Answer 25

The rate of reaction increase as enzyme concentration increases as there are more active site for substrates to bind to, however, increasing the enzyme concentration beyond a certain point has no effect on the rate of reaction as there are more active sites than substrates so substrate concentration becomes the limiting factor.

Question 26

Describe the effect on enzyme activity when substrate concentration increases.

Answer 26

As concentration of substrate increases, rate of reaction increases as more enzyme-substrate complexes are formed, however, beyond a certain point the rate of reaction no longer increases as enzyme concentration becomes the limiting factor.

Reference to Vmax (Card 34).

Question 27

What is an inhibitor?

Answer 27

An inhibitor is a substance which slows down or prevents a particular chemical reaction or process by reducing the activity of the reactant, catalyst or enzyme.

Question 28

What are the two types of reversible inhibitors?

Answer 28

Non-competitive and competitive inhibitors.

Question 29

What is a competitive inhibitor?

Answer 29

A competitive inhibitor is a molecule which has a similar shape to the substrate and fits into the enzyme’s active site preventing the substrate from binding. In this way, the competitive inhibitor molecule competes with the substrate to bind to the active site of an enzyme.

Question 30

What is a non-competitive inhibitor?

Answer 30

Non-competitive inhibitors bind to a different site that is not the active site on the enzyme, changing the shape of the enzyme so that it cannot bind to the substrate effectively.

Question 31

Describe the effect on enzyme activity when the concentration of competitive inhibitors increases.

Answer 31

As the concentration of competitive inhibitors increases, the rate of enzyme activity decreases because more active sites on the enzyme are occupied by the competitive inhibitor instead of the substrate. This reduces the number of enzyme-substrate complexes formed, leading to a decrease in the rate of enzyme activity.

Question 32

Describe the effect on enzyme activity when the concentration of non-competitive inhibitors increases.

Answer 32

When the concentration of non-competitive inhibitors increases, enzyme activity decreases. Non-competitive inhibitors bind to a different site that is not the active site on the enzyme, altering the enzyme’s shape and function, and reducing its ability to catalyze reactions regardless of substrate concentration.

Question 33

Describe the effect that non-competitive inhibitors have on an enzyme’s shape.

Answer 33

While the inhibitor is bound to the enzyme, it can affect the normal arrangement of hydrogen bonds and hydrophobic interactions holding the enzymes molecule in its three dimensional shape.

Question 34

What is Vmax?

Answer 34

Vmax is the maximum rate of an enzyme-catalyzed reaction. At this point, all active sites of the enzyme molecules are occupied, and the reaction rate cannot increase further regardless of additional substrate concentration.

Question 35

Describe how to decrease the effect of competitve inhibitors?

Answer 35

To decrease the effect of competitive inhibitors, increase the concentration of the substrate, which can outcompete the inhibitor for the active site.

Question 36

State what the Michaelis-Menten formula equation is (including units and meaning of formula terms?

Michaelis-Menten constant (Km).

Answer 36

V = Vmax [S] ÷ Km + [S]

V = initial reaction rate.
[S] = substrate concentration.
Vmax = maximum reaction rate.
Km = the Michaelis-Menten constant/substrate concentration at ½ Vmax.

Reference to enzyme affinity (Card 38).

This equation is used to compare the affinity of different enzymes for their substrates.

Question 37

What is Km?

Answer 37

The Michaelis-Menten equation is a measure of the substrate concentration at which the reaction rate is at half of its maximum value (Vmax)
It reflects the affinity of the enzyme for its substrate.

The Michaelis-Menten constant is Km.

Question 38

What is enzyme affinity?

Answer 38

Enzyme affinity refers to how strongly an enzyme binds to its substrate. High affinity means the enzyme binds tightly and easily to the substrate, while low affinity means the binding is weaker and less likely to occur.

Question 39

What does a low Km indicate and what does a high Km indicate?

The Michaelis-Menten constant is Km.

Answer 39

A lower Km indicates higher affinity, while a higher Km indicates lower affinity.

Question 40

What is an immobilised enzyme?

Answer 40

An immobilised enzyme is an enzyme that is attached to an insoluble, inert material such as agar gel.

Question 41

List for three advantages of immobilising enzymes.

Answer 41

• Immobilised enzymes are trapped and therefore not fully exposed to denaturing conditions and are more able to withstand changes to pH and temperature.
• Immobilising enzymes means that you can re-use the enzymes.
• Immobilising enzymes means that the product is enzyme-free.

Question 42

Remaining subtopics to write flashcards on.

Answer 42

• Calorimeters with enzymes.
• Disadvantages of immobilised enzymes.
• Advantages and disadvantages of free-use enyzmes.