2.1.4 - Enzymes

Question 1

What is an enzyme ?

Answer 1

A biological catalyst that increase the rate of chemical reactions without being used up

Question 2

Define the term ‘Metabolism’ ?

Answer 2

Metabolism - All the chemical reactions that occur within a living organism

Question 3

Define the term ‘Anabolic reaction’ ?

Answer 3

Anabolic reactions - The building of large molecules from smaller molecules

Question 4

Name an example of enzymes being involved in anabolic reactions ?

Answer 4

The synthesis of large polymer-based components in cells

Question 5

Define the term ‘Catabolic reactions’ ?

Answer 5

Catabolic reactions - The breakdown of larger molecules into smaller molecules

Question 6

Name an example of enzymes being involved in catabolic reactions ?

Answer 6

The breakdown of glucose to release energy

Question 7

Define the term ‘intercellular enzymes’ ?

Answer 7

Intercellular enzymes - Enzymes that catalyse reactions inside the ell that produced them

Question 8

Name an example of an intercellular enzyme ?

Answer 8

Catalase - An intercellular enzyme that catalyses the breakdown of hydrogen peroxide into oxygen and water. Hydrogen peroxide is a toxic product of many metabolic pathways therefore preventing its accumulation.

Question 9

Define the term ‘Extracellular enzymes’ ?

Answer 9

Extracellular enzyme - Enzymes that catalyse reactions outside the cell that produced them

Question 10

What is the role of extracellular enzymes ?

Answer 10

• Nutrients are often in the form of polymers and therefore too large to enter cell via the cell surface membrane
• Extracellular enzymes are used to break down the large nutrient molecules into smaller molecules so they can be absorbed by the cell

Question 11

Name an example of an extracellular enzyme ?

Answer 11

Amylase - It is an extracurricular enzyme that breakdown of starch to maltose. Maltase catalyses breakdown of maltose to glucose which os then small enough to be absorbed into bloodstream

Question 12

Define the term ‘Activation energy’ ?

Answer 12

Activation energy - The minimum amount of energy required for a chemical reaction to occur

Question 13

How do enzymes function ?

Answer 13

• Many different enzymes are produced by organisms, each enzyme catalysing one biological reaction making them specific ( specificity of enzyme )
• Enzymes help the molecules collide, lowering the activation energy required by the reaction and producing an alternative reaction pathway

Question 14

What are the two models for how enzymes function ?

Answer 14

• Lock and key hypothesis
• Induced-fit hypothesis

Question 15

Explain the lock and key hypothesis ?

Answer 15

• The tertiary structure of the enzyme determines the enzyme’s and enzyme’s active site’s shape which is complementary to a specific substrate molecule
• Lock and key hypothesis says that like only a specific key will fit into a lock / only a specific substrate will ‘fit’ in active site of enzyme
• When the substrate binds to the active site of an enzyme, an enzyme-substrate complex forms. Substrate then react leading to formation of product in enzyme-product complex which are then released leaving the enzyme to react is subsequent reactions

Question 16

Explain the induced-fit hypothesis ?

Answer 16

• The induced-fit hypothesis suggests the enzyme’s active site changes shape slightly when reacting with substrate
• When a substrate binds with active site of an enzyme, this induces a change in the enzymes tertiary structure so it becomes complementary to substrate
• This can put strain on substrate and weaken bonds in substrate lowering the activation energy of the reaction

Question 17

What are the factors affecting enzyme activity ?

Answer 17

• Temperature
• pH
• Substance concentration
• Inhibitors

Question 18

Explain the affect of temperature on enzyme activity ?

Answer 18

• As the temperature increases, the kinetic energy of particles increases causing the particles to move faster and collide more frequently per time period
• This means/ causes more frequent successful collisions between substrate and enzyme leading to an increased rate of reaction

Question 19

Explain the affect of extreme temperature on enzyme activity ?

Answer 19

• Enzymes are globular proteins and therefore their structure, therefore shape is affected by temperature
• As the temperature increases, bonds holding the protein together vibrate more until the bonds break
• This results in the change in the precise tertiary structure of the protein causing enzyme to change shape, active site to change shape and no longer remain complementary to substrate so called denatured
• Substrate can no longer bind to the enzymes active site so enzyme can no longer function

Question 20

What is the temperature coefficient ?

Answer 20

The temperature coefficient is measure of how much the rate of reaction increases with a 10oC rise in temperature

Question 21

What is the symbol of the temperature coefficient ?

Answer 21

Qv10

Question 22

What is the temperature coefficient of enzyme-controlled reactions ?

Answer 22

For enzyme-controlled reactions, the rare of reaction doubles as the temperature increases by 10oC ( Qv10 = 2 )

Question 23

Explain the affect of pH on enzyme activity ?

Answer 23

• When the pH is optimal, enzymes will remain their specific shape and canton optimally
• When the pH changes significantly the enzyme will denature

Question 24

Explain the affect of high pH on enzyme activity ?

Answer 24

This leads to enzyme becoming denatured

Question 25

Explain the affect of low pH on enzyme activity ?

Answer 25

• A low pH means more H+ ions are present
• This means less R-groups of amino acids are able to interact with one another leading to bonds breaking, the tertiary structure and shape of the enzyme to change

Question 26

Explain the affect of substrate concentration on enzyme activity ?

Answer 26

• When the substrate concentration increases, the number of collisions between substrates and enzymes active site increases per time period
• This causes the rate of formation of enzyme-complexes to increase, causing rate to increase
• This continues till all enzymes active site’s have become saturated and the rate reaches its max ( Vmax )
• Substrate concentration will no longer have any affect

Question 27

Explain the affect of enzyme concentration on enzyme activity ?

Answer 27

• As the enzyme concentration increases, the number of collisions between substrates and enzymes active site increases per time period
• This causes the rate of formation of enzyme-complexes to increase, causing rate to increase

Question 28

How can the Vmax be increased once substrate concentration no longer has an affect ?

Answer 28

Vmax can be increased by increasing enzyme concentration so more active sites are available leading to formation of enzyme-substrate complexes at a faster rate or by increasing temperature

Question 29

Define the term ‘Inhibitors’ ?

Answer 29

Inhibitors - Molecules that prevent enzymes from functioning normally/ catalysing chemical reactions

Question 30

What are the two type of inhibitors ?

Answer 30

• Competitive inhibitors
• Non-competitive inhibitors

Question 31

Explain how competitive inhibitors function ?

Answer 31

• Competitive inhibitors are a similar shape to the substrate that binds to the specific active site of an enzyme
• Competitive inhibitors will bind to active site of enzyme and prevent substance molecules from binding to specific active site reducing. number of substrates binding to enzymes, enzyme-substrate complexes forming and reducing rate of reaction
• Enzyme has been inhibited

Question 32

Explain the effect of competitive inhibitors on the rate of enzyme activity ?

Answer 32

• They reduce the rate of reaction but not Vmax
• This can be combated by increasing substrate concentration increasing number of substrates and therefore number of enzyme-substrate complexes forming till Vmax is reached

Question 33

Explain why the effect of competitive inhibitors is reversible ?

Answer 33

Most competitive inhibitors only bind to active site temporarily, so their effect is reversible

Question 34

Name examples of competitive inhibitors ?

Answer 34

• Statins
• Aspirin

Question 35

Explain how non-competitive inhibitors function ?

Answer 35

• Non-competitve inhibitors are molecules that kind to the enzyme at a point other than the active site ( allosteric site )
• This causes the enzymes tertiary structure to change and therefore its active site meaning it is no longer complementary to the substrate so it cannot bind to enzyme
• The enzyme can no longer carry out its function and is inhibited

Question 36

Explain the effect of non-competitive inhibitors on the rate of enzyme activity ?

Answer 36

They reduce the rate of the reaction as more active sites become unavailable

Question 37

Explain why the effect of non-competitive inhibitors is non-reversible ?

Answer 37

The structure of enzyme is permanently altered so increasing enzyme/ substrate concentration does not combat effect so non-reversible

Question 38

Name examples of non-competitive inhibitors ?

Answer 38

• Organophosphates
• Proton pump inhibitors

Question 39

Define the term ‘End-product inhibitor’ ?

Answer 39

End-product Inhibitor - Enzyme inhibition that occurs when the product of a reaction acts as an inhibitor to the enzyme that produces it

Question 40

What is the role of ‘end-product inhibitors’ ?

Answer 40

• They serve as negative feedback/ a control mechanism so excess products aren’t made and resources aren’t wasted
• Non-competitive reversible inhibition

Question 41

Define the term ‘cofactors’ ?

Answer 41

Cofactors - An additional non-protein component necessary for the effective functioning of an enzyme as a biological catalyst

Question 42

What are the different types of cofactors ?

Answer 42

• Cofactors ( Inorganic cofactors )
• Coenzymes ( Organic cofactors )
• Prosthetic groups ( Tightly bounds cofactors/ required by enzymes to carry out catalytic function )

Question 43

Where are inorganic cofactors obtained from ?

Answer 43

They are obtained via the diet as minerals

Question 44

Name an example of inorganic cofactors ?

Answer 44

Cl- ion in enzyme amylase - Enzyme amylase ( which catalyses the breakdown of starch ) contains a Cl- ion ( its inorganic cofactor ) that is necessary for formation of amylases correctly shaped active site

Question 45

Where are organic cofactors/ coenzymes obtained from ?

Answer 45

They are obtained from vitamins in diet