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A Level Biology > 4.1 - 4.4 - Enzyme Action, Inhibators, Factors Affecting Activity , Cofactors,coenzymes & Prosthetic Groups > Flashcards

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

1
Q

What are enzymes?

A

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

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2
Q

What type of proteins are enzymes?

A

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

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3
Q

What type of a structure do enzymes have ?

A

Tertiary structure

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4
Q

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

A

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

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5
Q

What is the process of the intracellular enzyme catalase ?

A

• 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

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6
Q

What is the process of the extracellular enzyme amylase ?

A

• 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

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7
Q

Explain the induced fit model of enzyme action

A

• 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

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8
Q

Explain the lock and key model of enzyme action

A

• 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

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9
Q

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

A

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

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10
Q

What is enzyme specificity?

A

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

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11
Q

How does substrate concentration affect rate of reaction?

A

•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

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12
Q

How does enzyme concentration affect rate of reaction?

A

•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

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13
Q

How does temperature affect the rate of enzyme controlled reactions?

A

•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)

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14
Q

What is the temperature coefficient?

A

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

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15
Q

How does ph affect the rate of reaction?

A

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

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16
Q

What is activation energy?

A

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

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17
Q

What is denaturation?

A

• 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

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18
Q

How do competitive inhibitors work?

A
  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
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19
Q

How do non-competitive inhibitors work?

A
  1. Bond at allosteric binding site
  2. Trigger conformational change of active site
  3. Increasing substrate concentration has no impact on their effect
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20
Q

What is end-product inhibition ?

A

•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

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21
Q

What are irreversible inhibitors?

A

• 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

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22
Q

What are reversible inhibitors?

A

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

23
Q

Define metabolic Poison

A

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

24
Q

Give some examples of metabolic poisons

A

Respiratory inhibitors include :

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

25
Q

How do some medicinal drugs act as inhibitors?

A

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

26
Q

What are inactive precursors in metabolic pathways?

A

•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

27
Q

What are coenzymes?

A

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

28
Q

What are inorganic cofactors?

A

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

29
Q

What are prosthetic groups?

A

Tightly bound cofactors act as permanent part of enzymes binding site

30
Q

Give an example of a competitive inhibitor?

A

Statin

31
Q

What is statin used in?

A

Synthesis of cholesterol

32
Q

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

A

Allosteric site

33
Q

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

A

Organophosphates

34
Q

What is a inhibitor?

A

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

35
Q

What is the process of competitive inhibition?

A

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

36
Q

What are competitive inhibitors?

A

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

37
Q

What are non-competitive inhibitors?

A

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

38
Q

What happens when you increase the concentration of an inhibitor?

A

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

39
Q

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

A

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

40
Q

What do reversible inhibitors act as?

A

Regulators in metabolic pathways

41
Q

How can metabolic reactions be controlled?

A

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

42
Q

How does non-competitive inhibition work?

A

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

43
Q

What is PPIs ? and what do they do ?

A

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

44
Q

What is end-product inhibition?

A

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

45
Q

What is PFK?

A

Phosphofructokinase

46
Q

Give 3 examples of non-reversible inhibitors as medicinal drugs

A

1) penicillin
2) Aspirin
3) eflornithine

47
Q

What is a cofactor ?

A

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

48
Q

What is precursor activation ?

A

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

49
Q

How are inorganic cofactors obtained ?

A

Via minerals

50
Q

How are organic coenzymes obtained ?

A

Via vitamins

51
Q

Are prosthetic groups cofactors or coenzymes ?

A

Cofactor

52
Q

What is another name or a precursor protein ?

A

Apoenzyme

53
Q

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

A

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

A Level Biology (54 decks)

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