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Enzymes Flashcards

1
Q

Define ‘enzyme’.

A
  • An enzyme is a biological catalyst which interacts with substrate molecules to facilitate chemical reactions.
  • Usually globular proteins.
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2
Q

Define ‘substrate’.

A
  • A reactant in a chemical reaction (when acted upon by an enzyme).
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3
Q

Define ‘prodcut’.

A
  • The end result of the reaction; enzymes act on substrates and convert them into products.
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4
Q

Why are enzymes necessary to life?

A
  • Enzymes control the processes and reactions of metabolism.
  • Without them, many reactions would take place too slowly to keep organisms alive.
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5
Q

Define ‘anabolic reactions’

A
  • Reactions of metabolism that construct molecules from smaller units.
  • Requires energy from the hydrolysis of ATP.
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6
Q

Define ‘catabolic reactions’

A
  • Reactions of metabolism that break down molecules to form smaller units.
  • Releases energy.
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7
Q

Define ‘digestion’

A
  • The catabolic process in the digestive tract where ingested food is converted into simple, soluble, and diffuse blue substances that can be assimilated by the body.
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8
Q

Define ‘metabolism’*

A
  • The chemical processes that occur within a living organism in order to maintain life.
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9
Q

How do enzymes affect both the structure and function of cells and whole organisms?

A
  • Enzymes control the processes inside cells, if those chemical reactions cannot take place, the cell cannot function.
  • If many cells are affected then the organism will feel its effects.
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10
Q

Define ‘intracellular enzyme’

A

Enzymes that act inside the cell e.g. DNA polymerase

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11
Q

Give an example of an Intracellular enzyme/

A

DNA polymerase

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12
Q

Define ‘extracellular enzymes’

A

Enzymes that are secreted and act outside cells e.g. amylase, lipase.

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13
Q

Give two examples of Extracellular enzymes.

A
  • Lipase
  • Amylase
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14
Q

State the substrates and products for the enzyme catalase.

A

Hydrogen peroxide into oxygen and water.

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15
Q

State the substrates and products for the enzyme amylase.

A

Starch into sugars.

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16
Q

State the substrates and products for the enzyme trypsin.

A

Proteins into polypeptides (which are further hydrolysed into amino acids by other enzymes).

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17
Q

Explain the role of extracellular enzymes in general.

A
  • Components for reactions often come from larger molecules that cannot enter cells but must be broken down so that the monomers can be used fro metabolism.
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18
Q

Summarise the digestion of starch as an example of the role of Extracellular enzymes.

A

Starch is broken down into individual glucose monomers that can be used for respiration.

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19
Q

Summarise the digestion of proteins as an example of the role of Extracellular enzymes.

A

Proteins are broken down into individual amino acids which can be used within cells to build the specific proteins needed.

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20
Q

Define ‘active site’

A

Area of an enzyme with a shape complementary to a specific substrate allowing the enzyme to bind to a substrate with specificity.

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21
Q

Define ‘complementary shape’

A

The shape of the active site and the substrate match so they fit together.

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22
Q

Define ‘specific’

A

Each enzyme has a single substrate that it works on that will fit its active site (or group of substrates — group specificity).

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23
Q

Explain why an enzyme only catalyses one type of reaction.

A
  • A substrate will only fit into an active site if it is complementary in both shape and charge.
  • And the reaction is only catalyses if the substrate binds with the active site.
  • This means that each enzyme only catalyses one type of reaction.
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24
Q

State the sequence of events in an enzyme-controlled reaction.

A
  1. Substrate fits into active site to form an enzyme-substrate complex. The active site changes shape to accommodate the substrate, and the complementary charges help the ‘fit’.
  2. The active site changes shape to convert the substrate into products. This is now an enzyme-product complex.
  3. The products no longer complement the active site and are released.
  4. The active site is now free for another substrate.
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25
Q

Describe the ‘lock and key’ hypothesis of enzyme action.

A
  • The active site is the lock, the substrate is the key.
  • One key fits only one lock.
  • This assumes that both the active site and substrate have a complementary fixed shape.
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26
Q

Describe the ‘induced-fit’ hypothesis of enzyme action.*

A
  • This has replaced lock and key theory.
  • It assumes the active site changes shape slightly to fit around the substrate.
  • The analogy used is a hand and a glove. The glove (active site) moves around the hand (substrate).
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27
Q

Suggest how the R-groups of amino acids are involved in catalysing reactions.

A
  • The active site may involve only a small number of amino acids but the R-groups are key to the function.
  • The interactions between them case the shape which must be complementary to the substrate.
  • They also may be charged which must be complementary.
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28
Q

Define ‘activation energy’

A

The energy required to initiate a reaction.

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29
Q

Define ‘rate of reaction’

A
  • How quickly or slowly the reaction takes places.
  • Measure of the change in concentration of the reactants or the change in concentration of the products per unit time.
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30
Q

State what the presence of an enzyme does to the activation energy for the reaction. Explain why this increases the rate of reaction.

A

Enzymes lower the activation energy requires for the reaction, making it easier for it to take place and therefore happen faster.

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31
Q

State 5 factors that affect the rate of an enzyme controlled reaction.

A
  1. Temperature
  2. pH
  3. Substrate concentration
  4. Enzyme concentration
  5. Inhibitors
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32
Q

Explain why increasing the temperature from below the optimum up towards the optimum increases the rate of reaction.

A

As temperature rises, enzymes and substrate molecules have more kinetic energy and move faster, forming more enzyme-substrate complexes.

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33
Q

Define ‘temperature coefficient, Q10’ and state its usual value for enzyme controlled reactions.

A
  • A measure of how much the rate of reaction increases with 10 degrees temperature increase.
  • For enzyme reactions, it is normally 2 (rate doubles every 10 degrees increase).
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34
Q

Explain why increasing the temperature up from the optimum decreases the rate of reaction abruptly.

A

Enzymes denature which changes the shape of active site so substrate cannot fit.

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35
Q

Explain why Siamese cats are white with black tails, ears, paws, and faces.

A
  • They have a mutation in the enzyme that catalyses melanin production which means tat it is denatures at normal body temperature.
  • The extremities of the cat such as the tail, however, are cooler so melanin is produced and the fur is darker.
36
Q

Explain why a pH change away from the optimum decreases the rate of reaction.

A
  • Enzyme structure depends on interactions of R groups.
  • pH alters charges and therefore bonds, changing and denaturing the enzyme, and therefore changing the shape of the active site.
  • So enzyme and substrate are no longer complementary.
37
Q

Define ‘Vmax’

A

Maximum initial velocity or rate of an enzyme-catalysed reaction.

38
Q

Explain how increasing the substrate concentration affects the initial rate of an enzyme-controlled reaction.

A
  • As substrate concentration increases, the rate of reaction also increases as there are free enzyme molecules to combine with the extra substrate.
  • At some point, the saturation point cannot increase further due to the enzymes working ‘flat-out’ — there are no longer any free enzymes to combine with extra substrate so increasing the concentration has no effect.
39
Q

Explain how increasing the enzyme concentration affects the initial rate of an enzyme-controlled reaction.

A
  • As enzyme concentration increases, rate increases as there will be free substrate waiting to be reacted with.
  • Rate will continue to increase until there is no longer an excess of substrate, and any extra enzymes are left free as there is no substrate to bind with.
40
Q

Describe and explain how to investigate any of the factors that affect the rate of enzyme-controlled reactions.*

A
  • Using catalase, hydrogen peroxide and measuring the rate (by measuring the volume of oxygen produced in a certain amount of time).
  • Change the conditions by using buffer solutions or water baths etc.
41
Q

Define ‘cofactor’

A

Non-protein components necessary for the effective functioning of an enzyme.

42
Q

Define ‘coenzyme’

A

If the cofactor is an organic molecule, it is a coenzyme.

43
Q

Give 2 possible roles of cofactor/coenzymes.

A
  • They may form part of the active site or transfer atoms/groups from one reaction to another through a multi-step pathway.
44
Q

Describe the similarities and differences between cofactors, coenzymes, and prosthetic groups.*

A
45
Q

Explain why the chloride ion necessary for the correct formation of the active site in amylase is called a cofactor and not coenzyme or prosthetic group.

A

It is an inorganic ion not permanently bound to the enzyme.

46
Q

Explain why the zinc ion that forms an important part of the structure of carbonic anhydrase is called a prosthetic group and not a cofactor or coenzyme.

A

It is an inorganic ion permanently bound to the enzyme.

47
Q

What is the responsibility of carbonic anhydrase?

A

It is an enzyme necessary for the metabolism of carbon dioxide.

48
Q

Give two examples of coenzymes that are synthesised from vitamins in our diet.

A
  • NAD is synthesised from vitamin B3 and is used in respiration to transfer hydrogen.
  • Coenzyme A is synthesised from vitamin B5 and used in the breakdown of carbohydrates and fatty acids in respiration.
49
Q

What coenzyme is synthesised from vitamin B3?

A

NAD — used in respiration to transfer hydrogen.

50
Q

What coenzyme is synthesised from vitamin B5?

A

Coenzyme A — used in the breakdown of carbohydrate and fatty acids in respiration.

51
Q

Describe 4 ways in which multi-step reaction pathways can be regulated by cells.

A
  1. Non-competitive inhibitor
  2. Competitive inhibitor
  3. End product inhibition
  4. Inactive precursor enzymes
52
Q

Define ‘enzyme inhibitors’

A

A factor that prevents or reduces the rate of an enzyme catalysed reaction.

53
Q

Define ‘competitive inhibitor’

A

An inhibitor that competes with the substrate to bind to the active site of an enzyme.

54
Q

Define ‘non-competitive inhibitor’

A

An inhibitor that binds to an enzyme at the allosteric site of an enzyme.

55
Q

Define ‘reversible inhibitor’

A

An inhibitor that can bind temporarily to the enzyme but also dissociate itself so the enzyme returns to being functional.

56
Q

Define ‘irreversible inhibitor’

A

An inhibitor that, once bound to the enzyme, cannot dissociate and permanently stops the enzyme functioning.

57
Q

Define ‘allosteric site’

A

The place on an enzyme where a molecule that isn’t the substrate may bind, thus changing the shape of the enzyme and influencing its ability to be active.

58
Q

Explain how a competitive inhibitor affects the rate of an enzyme-controlled reaction.

A
  • They have a similar shape to the substrate so enter the active site forming an enzyme-inhibitor complex.
  • No product is formed but while the inhibit is in the active site, the substrate cannot enter.
59
Q

State two examples of competitive inhibitors and describe their action.

A
  1. Statins are competitive inhibitor of the enzymes used to produce cholesterol so are prescribed to help lower cholesterol.
  2. Aspirin inhibits the production of chemicals responsible for pain and fever.
60
Q

Describe the inhibitor ‘statins’.

A
  • Competitive
  • Inhibits enzyme which produces cholesterol so statins are prescribed to help lower cholesterol levels.
61
Q

Describe the inhibitor ‘aspirin’.

A
  • Competitive inhibitors
  • Inhibits the production of chemicals responsible for pain and fever.
62
Q

Explain how a non-competitive inhibitor affects the rate of an enzyme-controlled reaction.

A
  • They don’t bind to the active site but to the allosteric site which distorts the tertiary structure which changes the shape of the active site so the substrate cannot fit.
63
Q

State two examples of a non-competitive inhibitors and describe their action.

A
  1. Organophosphate used as insecticides as they inhibit enzymes used in nervous impulses transmission causing paralysis.
  2. Proton pump inhibitors block an enzyme responsible for secreting hydrogen ions into the stomach, preventing build-up of acid which could lead to ulcers.
64
Q

Describe the inhibitor ‘Organophosphate’.

A
  • Non-competitive
  • Used as insecticides as it inhibits the enzyme used in nervous impulse transmission, causing paralysis.
65
Q

Describe the inhibitor ‘proton pump’.

A
  • Non-competitive
  • Block an enzyme responsible for secreting hydrogen ions into the stomach, preventing build up of acid which could lead to ulcers.
66
Q

Define the term ‘end-product inhibition’.

A

The product of a reaction inhibits the enzyme required for the reaction.

67
Q

Describe the usefulness of end-product inhibitor in controlling metabolic pathways.

A
  • Useful as if there is little product, there is little inhibitor therefore more is made.
  • If there is a lot of product, there is lots of inhibitor and production slows down.
  • Negative feedback controls the level of product.
68
Q

Describe how ATP is involved in end-product inhibitor of the enzyme phosphofructokinase.

A
  • First step of break-down of glucose involves adding 2 phosphate groups to the molecule.
  • Addition of second catalysed by PFK which is competitively inhibited by ATP so it regulates its own production.
69
Q

Define ‘inactive precursor’

A

A protein precursor (is an inactive protein or peptide) that can be turned into an active form by post-translational modification, such as breaking off a piece of the molecule or adding on another molecule.

70
Q

Why are some enzymes produced in the form of ‘inactive precursor enzyme’?

A

Some enzymes can cause damage to cells and must only be activated under certain conditions.

71
Q

Describe 3 ways in which inactive precursors may be activated.

A
  1. Addition of a cofactor.
  2. Action of another enzyme e.g. protease.
  3. Change in conditions e.g. pH.
72
Q

Define ‘apoenzyme’

A
  • An inactive enzyme.
  • Activation of the enzyme occurs upon binding of an organic or inorganic cofactor.
73
Q

Define ‘holoenzyme’

A

An enzyme with its required cofactor.

74
Q

Define ‘zymogen’/‘proenzyme’

A

An inactive substance which is converted into an enzyme when activated by another enzyme.

75
Q

Give 2 examples of inactive precursor enzymes and describe how they are activated.

A
  1. Factor X: During blood clotting, factor X is released by platelets which catalyses prothrombin into thrombin (which is a protease which catalyse fibrinogen into fibrin) — this series of activations is called the coagulation cascade.
  2. Pepsinogen released into stomach becomes pepsin due to pH — this protects body tissues from digestive actions of Pepsin.
76
Q

What is the coagulation cascade?

A

During blood clotting, factor X is released by platelets which catalyses prothrombin into thrombin — which is a protease which catalyses fibrinogen into fibrin.

77
Q

How many amino acids are there?

A
  • 20 that form different polypeptides.
  • Each with a different R-group
78
Q

What is the primary structure of proteins?

A

Polypeptides

79
Q

Polypeptides fold to form _____

A
  • Specific tertiary structures which allow them to carry out specific roles in the body.
80
Q

Describe two poisons/drugs which are involved in enzyme inhibition.

A
  1. Potassium cyanide: Inhibits an enzyme involved in aerobic respiration, thus someone poisoned with cyanide will be dead within hours.
  2. Competing inhibitors of protease enzymes may be useful in treatment of viral diseases such as HIV. Viruses have a protein coat; therefore, inhibiting the virus’s protease enzymes prevents repair to the coat so the enzyme disintegrates.
81
Q

What are a common source of coenzymes in humans?

A

Nutrients

82
Q

Describe the secondary structure of proteins.

A
  • Weak hydrogen bonds between the hydrogen (amino group) and oxygen (Carboxyl group) cause the polypeptide to from a-helix.
83
Q

Describe the tertiary structure of proteins.

A
  • Ionic bonds, disulfide bridges, and hydrophobic/hydrophilic interactions case the helix to fold into a 3d shape.
84
Q

Describe the quaternary structure of proteins.

A
  • Formed of multiple proteins and non-protein (prosthetic) substances.
  • E.g. Haemoglobin has four proteins and four ions.
85
Q

Describe fibrous proteins.

A
  • Long, unbranched, and tightly-wound together.
  • Have structural functions, such as collagen in muscles, keratin in hair, and elastin in connective tissues.
86
Q

Describe globular proteins.

A
  • Smaller than fibrous proteins.
  • Can easily be secreted from a cell.
  • Have metabolic functions e.g. enzymes (maltase) and hormones (insulin).
87
Q

What type of structure are do enzymes have?

A

Tertiary structure

Biology (25 decks)

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