4.1 - 4.4 - Enzyme Action, Inhibators, Factors Affecting Activity , Cofactors,coenzymes & Prosthetic Groups

Question 1

What are enzymes?

Answer 1

proteins that act as biological catalysts for intra & extracellular reactions to determine structure and function

Question 2

What type of proteins are enzymes?

Answer 2

They’re Globular proteins that interact with substrate molecules causing them to react at much faster rates without the need for harsh environmental conditions

Question 3

What type of a structure do enzymes have ?

Answer 3

Tertiary structure

Question 4

What are intracellular and extracellular enzymes and what are some examples?

Answer 4

Intracellular - produced and function inside the cell eg. Respiration, photosynthesis, glycogen and protein synthesis
Extracellular - secreted by cells and catalyse reactions outside the cells
Eg. Bacteria and fungi , decomposer organisms

Question 5

What is the process of the intracellular enzyme catalase ?

Answer 5

• hydrogen peroxide is produced as a by product of many metabolic reactions
• harmful to cells
• catalase converts hydrogen peroxide into water and oxygen preventing any damage to cells or tissues

Question 6

What is the process of the extracellular enzyme amylase ?

Answer 6

• digestion is usually carried out by extracellular enzymes
• due to the fact that the macromolecules being digested are too large to enter the cell
• amylase is involved in carbohydrate digestion it hydrolyses starch into simple sugars
• secreted by the salivary glands and pancreas for digestion of starch in the mouth and small intestine

Question 7

Explain the induced fit model of enzyme action

Answer 7

• in this model the enzyme and substrate interact with each other
• the enzyme and it’s active site can change shape slightly as the substrate molecule enters the enzyme
• these changes in shape are called conformational changes
• conformational changes ensure an idea of ideal binding arrangement between the enzyme and substrate is achieved
• this maximises the ability of the enzyme to catalyse the reaction
• the initial interaction between the enzyme and substrate is relatively weak but these weak interactions rapidly induce changes in the enzymes in tertiary structure
• that strengthen binding puts a strain on the substrate molecule - weakens bonds in the substrate - lowering activation energy

Question 8

Explain the lock and key model of enzyme action

Answer 8

• suggests that active site has a rigid shape determined by the tertiary structure
• thus is only complimentary to 1 substrate
• formation of ES complex lowers activation energy
• bonds in enzyme product complex are weak do product desorbs

Question 9

Name 5 factors that affect the rate of enzyme-controlled reactions

Answer 9

• enzyme concentration
• substrate concentration
• concentration of inhibitors
• pH
• temperature

Question 10

What is enzyme specificity?

Answer 10

The specificity of an enzyme is a result of the complimentary nature between the shape of the active site on the enzyme and it’s substrate

Question 11

How does substrate concentration affect rate of reaction?

Answer 11

•Given that enzyme concentration is fixed = rate increases proportionally to substrate concentration
• the rate levels off when maximum number of ES complexes form at any given time

Question 12

How does enzyme concentration affect rate of reaction?

Answer 12

•Given that substrate is in excess = rate increases proportionally to enzyme concentration
• rate levels off when maximum number of ES complexes form at any given time

Question 13

How does temperature affect the rate of enzyme controlled reactions?

Answer 13

•Rate increases as kinetic energy increases & peaks at optimum temperature
• above optimum , ionic & H bonds in 3° structures break = active site is no longer complimentary to substrate (denaturation)

Question 14

What is the temperature coefficient?

Answer 14

Q10 measures the change in rate of reactions per 10°c temperature increase
Q10 = R2/R1 ( wheee R represents Rate )

Question 15

How does ph affect the rate of reaction?

Answer 15

Enzymes have a narrow optimum pH range
Outside range , H+/ OH- ions interact with H- bonds and ionic bonds in 3° structure = denaturation

Question 16

What is activation energy?

Answer 16

Amount of energy required by the substrate to become just unstable enough for a reaction to occur and for products to be formed

Question 17

What is denaturation?

Answer 17

• when temperatures are too high the increased kinetic energy and vibration of the enzyme molecules put a strain on them - causing the weaker hydrogen and ionic bonds that hold the enzyme molecule in its precise shape to start to break
• breaking of bonds = tertiary structure of protein to change = active site is permanently damaged = shape Is no longer complementary to the substrate = preventing the substrate from binding

Question 18

How do competitive inhibitors work?

Answer 18

1. Bind to active site since they have similar shape to substrate
2. Temporarily prevent ES complexes from forming until released
3. Increasing substrate concentration decreases their effect

Question 19

How do non-competitive inhibitors work?

Answer 19

1. Bond at allosteric binding site
2. Trigger conformational change of active site
3. Increasing substrate concentration has no impact on their effect

Question 20

What is end-product inhibition ?

Answer 20

•One of the products of a reaction acts as a competitive or non competitive inhibitor for an enzyme involved in the pathway
• prevents further formation of products

Question 21

What are irreversible inhibitors?

Answer 21

• permanently prevent formation of ES Complexes
• heavy metal ions eg. Mercury, silver cause disulphide bonds in tertiary structure to break
• bind to enzymes by strong covalent bonds eg. Cyanide binds to cytochrome

Question 22

What are reversible inhibitors?

Answer 22

May be competitive or-non-competitive
• bond to enzyme temporarily eg. By H- bonds or a few ionic bonds
• ES complexes can firm after the inhibitor is released

Question 23

Define metabolic Poison

Answer 23

Substance that damages cells by interfering with metabolic reactions , usually an inhibitor

Question 24

Give some examples of metabolic poisons

Answer 24

Respiratory inhibitors include :

• cyanide- non competitive, irreversible, inhibits cytochrome c oxidase
• malonate - competitive, inhibits succinate dehydrogenase
• arsenic - competitive, inhibits pyruvate dehydrogenase

Question 25

How do some medicinal drugs act as inhibitors?

Answer 25

Penicillin- non competitive inhibitor of transpeptidase to prevent formation of peptidoglycan cross-links in bacterial cell wall

Ritonavir - inhibits HIV protease to prevent assembly of new virions

Question 26

What are inactive precursors in metabolic pathways?

Answer 26

•To prevent damage to cells, some enzymes in metabolic pathways are synthesised as inactive precursors eg. Proteases
• one part of the precursor acts an inhibitor
• ES complexes form when it is removed

Question 27

What are coenzymes?

Answer 27

•Organic cofactors - do not bind permanently - often transport molecules or electrons between enzymes
• frequently derived from water- soluble vitamins

Question 28

What are inorganic cofactors?

Answer 28

Facilitate temporary binding between substrate and enzyme
Often metal ions eg. Cl- is the cofactor for amylase

Question 29

What are prosthetic groups?

Answer 29

Tightly bound cofactors act as permanent part of enzymes binding site

Question 30

Give an example of a competitive inhibitor?

Answer 30

Statin

Question 31

What is statin used in?

Answer 31

Synthesis of cholesterol

Question 32

What is the alternative site that non-competitive inhibitors bind to?

Answer 32

Allosteric site

Question 33

What is an example of an irreversible non- competitive inhibitor used in pesticides and herbicides?

Answer 33

Organophosphates

Question 34

What is a inhibitor?

Answer 34

Molecules that prevent enzymes from carrying out their normal function of catalysis, it affects the binding of substrate to the enzymes

Question 35

What is the process of competitive inhibition?

Answer 35

1 ) a molecule or part of a molecule that has a similar shape to the substrate of an enzyme can fit into the active site of the enzyme
2 ) this blocks the substrate from entering the active site , preventing the enzyme from catalysing the reaction
3 ) the enzyme cannot carry out its function and thus is said to be inhibited
4 ) the non substrate molecule that binds to the active site is a type of inhibitor
5 ) substrate and inhibitor molecules present in a solution will compete with each other to bind to the active sites of the enzymes catalysing the reaction
6 ) this will reduce the number of substrate molecules binding to the active sites in a given time and slows down the rate of reaction

Question 36

What are competitive inhibitors?

Answer 36

Have a similar shape to that of the substrate molecules and there fore compete with the substrate for the active site

Question 37

What are non-competitive inhibitors?

Answer 37

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 38

What happens when you increase the concentration of an inhibitor?

Answer 38

Reduces the rate of reaction and if the inhibitor concentration continues to be increased the reaction will stop completely

Question 39

In non competitive inhibition what happens when you increase the substrate concentration?

Answer 39

This 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 40

What do reversible inhibitors act as?

Answer 40

Regulators in metabolic pathways

Question 41

How can metabolic reactions be controlled?

Answer 41

By using the end product of a particular sequence of metabolicreactions as a non-competitive, reversible inhibitor

Question 42

How does non-competitive inhibition work?

Answer 42

1) the inhibitor binds to the enzyme at a location other than the active site
- this alternative site is called an allosteric site
2) the binding of the inhibitor causes the Tertiary structure of the enzyme to change - meaning the active site changes shape
3) this results in the active site no longer having a complementary shalt to the substrate so it is unable to bind to the enzyme
4 ) the enzyme cannot carry out its function and is said to be inhibited

Question 43

What is PPIs ? and what do they do ?

Answer 43

-Proton pump inhibitors
- used to treat long term indigestion
- they irreversibly block an enzyme system responsible for secreting hydrogen ions into the stomach

Question 44

What is end-product inhibition?

Answer 44

Occurs when the product of a reaction acts as an inhibitor to the enzyme that produces it

Question 45

What is PFK?

Answer 45

Phosphofructokinase

Question 46

Give 3 examples of non-reversible inhibitors as medicinal drugs

Answer 46

1) penicillin
2) Aspirin
3) eflornithine

Question 47

What is a cofactor ?

Answer 47

A non protein that is obtained via the diet as minerals that transfer atoms or groups from one reaction to the other in a multi-step pathway or form part of the active site on the enzyme

Question 48

What is precursor activation ?

Answer 48

Precursor enzymes need to undergo a process of change in order to be activated - this involve the addition of a cofactor

Question 49

How are inorganic cofactors obtained ?

Answer 49

Via minerals

Question 50

How are organic coenzymes obtained ?

Answer 50

Via vitamins

Question 51

Are prosthetic groups cofactors or coenzymes ?

Answer 51

Cofactor

Question 52

What is another name or a precursor protein ?

Answer 52

Apoenzyme

Question 53

Explain what is meant by the term Vmax with respect to enzymes

Answer 53

The reaction is at a maximum rate and all active sites are occupied and enzyme activity is at a maximum