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BIOLOGY A LEVEL > CHAPTER 4 - ENZYMES > Flashcards

CHAPTER 4 - ENZYMES Flashcards

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1
Q

What are enzymes?

A

Biological catalysts (made from proteins)

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2
Q

What type of proteins are Enzymes?

A

Globular

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3
Q

What do Enzymes do?

A

Interact with substrate molecules causing them to react at much faster rates without the need for harsh environmental conditions

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4
Q

What do anabolic enzymes catalyse?

A

Build up reactions

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5
Q

What to catabolic enzymes catalyse?

A

Break down reactions

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6
Q

What is Vmax?

A

Maximum initial velocity or rate of the enzyme catalysed reaction, Position where enzymes cannot speed up reaction rates any further

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7
Q

What is the specificity of an enzyme?

A

Each enzyme catalyses only one type of biochemical reaction

(Means there are thousands of enzymes in a given cell)

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8
Q

What is activation energy

A

Amount of energy required to start a reaction - cause a successful collision

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9
Q

What are the two hypothesis on how enzymes react?

A

Lock and Key Hypothesis

Induced-fit hypothesis

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10
Q

What is the Lock and Key Hypothesis?

A

Only a specific substrate will fit into the active site of the enzyme

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11
Q

What is the area in on enzyme where Enzymes react?

A

Active site

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12
Q

How do enzymes react

A

Substrate(s) successfully randomly collides with active site

Substrate(s) binds to enzyme and forms Enzyme-Substrate Complex

Substrate held so that atom-groups are close enough to react

Forms temporary bonds with R-groups of substrate to strain the bonds in substrate,

Substrate(s) react, forms Enzyme-product complex

Products are released, Enzyme is unchanged

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13
Q

What is the induced-fit hypothesis?

A

Enzyme changes shape as the substrate enters

Initial interaction between enzyme and substrate is weak, but these induce changes in enzymes tertiary structure

Which strengthens binding, putting strain on molecule

Can weaken particular bonds, therefore lowering activation energy

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14
Q

What are Intracellular enzymes?

A

Enzymes that remain within the cell

(eg breakdown of Hydrogen Peroxide, making polysaccharides from glucose)

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15
Q

What are extracellular enzymes?

A

Enzymes that operate outside of the cell

(eg breakdown of large molecules into smaller ones in digestion, which then gets absorbed by cells)

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16
Q

Examples of Extracellular enzymes

A

Amylase

Trypsin

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17
Q

Describe the digestion of starch

A

Starch polymers are partially broken down into maltose (Disaccharide) by Amylase

Maltose is broken down into glucose (monosaccharide) by maltase

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18
Q

Where is Amylase produced and released

A

produced by salivary glands and pancreas

Released into mouth and small intestine

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19
Q

Where is maltase released?

A

Small intestine

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20
Q

Why is glucose a desired product of the digestion of starch?

A

Small enough to be absorbed by cells lining digestive system and absorbed into blood stream

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21
Q

What are protease enzymes?

A

Enzymes that catalyses digestion proteins

Eg Trypsin

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22
Q

What does Trypsin do?

A

Digests proteins into smaller peptides, then subsequently broken down into amino acids by other proteases

Amino acids can then be absorbed by cells lining digestive system and then absorbed by the bloodstream

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23
Q

Where is trypsin produced and released?

A

Produced in pancreas

Released by pancreatic juices in small intestine

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24
Q

State the type of biological molecule used to form enzymes

A

Protein

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25
Q

Name the monomers that form the biological molecule that makes enzymes

A

Amino Acids

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26
Q

Describe how the structure(s)of this biological molecule determines enzyme activity

A

Specific, 3D shape / tertiary structure

(formation of) active site

binds to substrate(s)

catalyses reaction

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27
Q

Explain how catabolism and anabolism are related to metabolism

A

Catabolism is breaking down of molecules

anabolism is building of molecules

reactions involve breaking down and building of molecules

Metabolism is sum of all reactions

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28
Q

There are two theories explaining enzyme substrate interaction. The Lock and key model and induced fit model of enzyme action
A) explain what is meant by the term model in the sentence above
B) Explain how the Following terms are relevant to each of the models. Complementary, flexibility, R group Interactions, Bond strain

A

A) simple / easy to understand

representation

B) Lock and key substrate is complementary to active site (of enzyme)

Induced fit active site is flexible

Both models substrate interacts with R groups in active site (binds)

(leading to) bond strain in substrate molecule

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29
Q

What factors affect enzyme activity?

A

Temperature

pH

Substrate and Enzyme Concentration

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30
Q

What affect do extremes in pH and Temperature do to most enzymes?

A

Causes Denaturing and a change in shape of their active site

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31
Q

What is the Temperature Coefficient or Q10

A

A measure of how much the rate of reaction increases with a 10 degree rise in temperature

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32
Q

What happens during the denaturing of an enzyme due to high temperature

A

Bonds holding proteins together vibrate more

As the temperature increases, vibrations increase

Causes bonds to strain then break

Changes Tertiary Structure, Active sit has changed, no longer acts as a catalyst as its active site cannot accept substrate

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33
Q

What is Optimum temperature of an enzyme?

A

The temperature at which the enzyme has the highest rate of activity

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34
Q

Are all enzymes optimum temperatures the same?

A

No, most in human body are around 40 degrees

Thermophilic bacteria (found in hot springs) is around 70 degrees

Psychrophilic organisms (live in areas of cold) can be below 5 degrees

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35
Q

Why are enzymes that are adapted to the cold more likely to denature after a small temperature change?

A

More flexible structures, making them less stable than enzymes that work at higher temperatures

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36
Q

Why are enzymes that are adapted to the heat more stable than other enzymes?

A

Increased number of bonds (especially Hydrogen and disulphide bridges) and are more resistant to change

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37
Q

What does tyrosinase catalyse?

A

The production of melanin (pigment responsible for dark coloured fur)

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38
Q

Why are Siamese cats extremities (tail, ears, limbs) dark when their fur is Cream/white?

A

Tyrosinase is at too low a temperature and is too low to denature the mutant tyrosinase, so black fur pigment is still catalysed

39
Q

What is the optimum pH of an enzyme?

A

Where the active site will only be in the right shape at that certain hydrogen ion concentration

40
Q

Why will enzymes denature under changes in pH?

A

Differing H+ ion concentration affects interactions between the polar and charged R-groups present in the amino acids

41
Q

What happens to an enzyme when the pH changes slightly

A

The Active site will change shape, but not denature

Will return to shape once pH returns to optimum

42
Q

What happens if the pH changes Drastically?

A

The structure of the enzyme is irreversibly altered and the active site will no longer be complementary to the substrate .

43
Q

Examples of Enzymes and their Optimum pHs and where they operate
Amylase
Pepsin
Maltase

A

Amylase - pH 7-8 - Mouth
Pepsin - pH 1-2 - Stomach
Maltase - pH 8 - Small Intestine

44
Q

Suggest why Siamese Kittens are born completely white

A

Extremities are at, same temperature as rest of the body in womb

Tyrosinase, not denatured

pigment is broken down

45
Q

Why does an increasing substrate concentration increase rate of reaction?

A

higher collision rate with active site of enzymes

More Enzyme-substrate complexes are formed

increases up until Vmax

46
Q

Why does an increasing enzyme concentration increase rate of reaction?

A

Increase number of available active sites in a particular volume,

more Enzyme-substrate complexes are formed

Increases up until Vmax

47
Q

Once Vmax is reached, how would you increase Rate of Reaction?

A

Increase Temperature

Add more enzyme

48
Q

Suggest an experiment into how different factors would effect enzyme activity

A

Placing Liver tissue (containing catalase) into a conical flask of Hydrogen peroxide with a gas syringe (or water trough technique)

Repeat experiment for Boiled and un-boiled liver

49
Q

Explain why a student would use liver tissue to investigate the effects of different factors on enzyme activity

A

Easy to obtain

contains catalase

50
Q

Show the chemical reaction that occurs resulting in the release of oxygen from the decomposition of Hydrogen Peroxide by Catalase

A

2H2O2 ➝ 2H2O + O2

51
Q

Explain the shape of the graph (page 91) for the gas production from Un-Boiled liver

A

volume of oxygen released increased

figures quoted

Catalase, catalysed reaction

52
Q

Describe and explain what has happened in the second experiment - involving boiled liver in the decomposition of H2O2 into oxygen and water

A

Enzymes are proteins

(boiling) denatures protein

Tertiary structure (of protein) changed

Active site no longer complementary to substrate

Fewer enzyme-substrate complexes formed

Decreased reaction rate

53
Q

What is a serial dilution?

A

A repeated stepwise dilution of a stock solution of known concentration (usually done by a factor of 10)

54
Q

How would a serial dilution be set up?

A

Add 1ml of stock solution with 9ml distilled water (1/10)

Take 1ml of this and add 9ml of distilled water (1/100)

Take another 1ml of this and add 9ml of distilled water (1/1000)

Etc……

55
Q

You are provided with a stock solution of enzyme X with a concentration of 20mmol/dm-3. Explain how you would prepare a range of five solutions with a different concentrations of enzyme X using the stock solution. Show your working and state concentrations produced

A

Serial dilution (1);

described e.g., 1 ml of stock solution and 9 ml of distilled water, 2 mmol dm−3 solution

repeat with diluted solution (s) 0.2 mmol dm−3 and 0.02 mmol dm−3 and 0.002 m mol dm−3 (1)

56
Q

Explain the term ‘denatured’ with reference to enzymes

A

R-group interactions are disrupted

Change in tertiary structure

change in 3D shape of active site preventing binding with substrate

57
Q

Bacteria that colonise hydrothermal vents, where temperatures are very high, have enzymes with high optimum temperatures. Suggest why these bacteria are unlikely to cause infections in humans

A

Bacterial enzymes have high optimum temperatures,

human body temperature is lower

Enzymes will have low activity

Bacteria will not thrive

58
Q

Enzymes with very low optimum temperatures tend to have quite flexible. Using your knowledge of collision theory, explain why this flexibility is necessary

A

(at low temperatures) Kinetic energy is low

substrates / enzymes, move slowly

Fewer collisions

Collisions have less energy

Increased flexibility of active site

increases chances of successful collision

59
Q

Why is it important that sometimes reactions do not happen too fast?

A

Could lead to the build up of (harmful) excess products

60
Q

How can enzymes be inactivated

A

Inhibitors

61
Q

What are the types of Inhibitors

A

Competitive

Non-competitive

62
Q

What do inhibitors do

A

Prevents enzymes carrying out their normal function of catalysis

63
Q

How does Competitive inhibition work

A

A molecule with a similar shape to active site blocks substrate from entering

Stops enzyme catalysing reaction

Enzyme cannot carry out function (inhibited)

Most bind reversibly to active site, exception aspirin

64
Q

How do competitive inhibitors affect rate of reaction?

A

Reduces rate of reaction, doesn’t change Vmax

If substrate concentration is increased, Original Vmax can still be reached

65
Q

Example of competitive inhibition

A

Statins inhibit enzyme used in synthesis of cholesterol
Prescribed to help people reduce blood cholesterol concentration and reduce risk of heart disease

Aspirin irreversibly inhibits COX enzymes, preventing synthesis of Prostaglandins and thromboxane, chemicals responsible for pain and fever

66
Q

How does Non-competitive inhibition work?

A

Inhibitor binds to location other than active site (Allosteric site)

Binding causes change in tertiary structure of enzyme, changes active site

Active site no-longer complementary, substrate cannot bind to enzyme

Cannot carry out function - said to be inhibited

67
Q

How do non-Competitive inhibitors affect rate of reaction?

A

Affects Vmax and reduces Rate of Reaction

Increasing concentration of inhibitor will decrease rate of reaction as more active sites become unavailable

68
Q

Examples of Irreversible non-competitive inhibitors

A

(often toxic)

Organophosphates used as insecticides and herbicides will inhibit enzyme acetyl cholinesterase, necessary for nerve impulse transmission

Leads to muscle cramps, paralysis and death if accidentally ingested

69
Q

What is End-product inhibition?

A

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

70
Q

What type of feedback is End-product Inhibition and why is it beneficial?

A

Negative feedback

Acts as control mechanism so excess products are not made and resources aren’t wasted

71
Q

Explain why a non-competitive inhibitor does not need to have a similar shape to a substrate molecule

A

A non-competitive inhibitor binds to an enzyme away from the active site

at an allosteric site

Which has a different shape than the active sit

72
Q

Explain why increasing the concentration of substrate will never produce the Vmax of a reaction after the addition of a non-competitive inhibitor

A

Inhibitor will always be present

Some enzymes always inhibited

73
Q

End-product inhibition is likely to be competitive rather than non-competitive. Suggest reasons for this, and give an example of end-product inhibition

A

End-product inhibition regulates rate of reaction

concentrations of substrate and product determine reaction rate

(so must be) competitive

substrate concentration has no effect in non- competitive inhibition

e.g. ATP and PFK in respiration

74
Q

What is an example of an End-product inhibition

A

ATP and PFK in respiration

Addition of two phosphates to glucose

Addition of second phosphate group results in the initial breakdown of glucose, catalysed by Phosphofructokinase (PFK)

This enzyme is competitively inhibited by ATP, Therefore ATP regulates its own production

When levels of ATP are high, ATP binds to allosteric site on PFK, preventing addition of second phosphate on glucose, so ATP is not produced at the same rate

As ATP is used up, less binds to PFK, so enzyme is able to add Second phosphate group to glucose, respiration resumes leading to production of more ATP

75
Q

Ethylene Glycol present in antifreeze is poisonous when ingested. Ethylene glycol is oxidised using the same enzymes used to oxidise ethanol. The product made during the breakdown of ethylene glycol, rather than ethylene glycol itself, are responsible for the toxic effects. Ethylene glycol is able to leave the body unchanged in urine. Suggest why ethanol is often used in emergency departments as an antidote to antifreeze poisoning.

A

Ethanol has similar shape to ethylene glycol

(ethanol) binds to active site of enzyme which breaks down ethylene glycol

competitive inhibition

less ethylene glycol broken down

more (ethylene glycol) leaves body unchanged

fewer toxic effects

76
Q

What is a cofactor?

A

A non-protein helper component that is needed to carry out enzyme function.

Transfer atoms or groups from one reaction or may form active site of an enzyme

77
Q

What is a Coenzyme?

A

If a cofactor is an organic molecule

78
Q

How are inorganic cofactors obtained?

A

Via Diet as minerals eg. iron, calcium, chloride and Zinc

79
Q

What ion acts as a cofactor to Amylase?

A

Chloride ion - forms part of active site

80
Q

How are coenzymes obtained?

A

Derived from vitamins in diet

81
Q

What Vitamin is a coenzyme of NAD?

A

Vitamin B3 - Transfers hydrogen atoms between molecules in respiration

82
Q

What does a Prosthetic group act as, a cofactor or coenzyme?

A

Permanent Cofactor (eg Zinc in carbonic anhydrase)

83
Q

What is inactive precursor enzymes?

A

When enzymes are produced in an inactive form, usually those that can cause damage within cells (needs to be controlled)

84
Q

How do Inactive precursor enzymes become active?

A

Change in Tertiary (structural) shape, particularly to active site, usually by addition of a cofactor

85
Q

What is an inactive precursor protein called before a cofactor is added?

A

Apoenzyme (inactive enzyme)

86
Q

What is a precursor inactive enzyme called after a cofactor is added

A

Holoenzyme (active enzyme now)

87
Q

How else can tertiary structure be changed to activate an enzyme?

A

Actions of another enzyme (eg protease) which cleaves certain bonds in the molecule

pH and temperature can also result in a change in structure (these are called zymogens or proenzymes)

88
Q

What is an example of enzyme activation by pH?

A

Inactive pepsinogen released into stomach to digest proteins, pH transforms enzyme into active pepsin

This adaption protects the body tissues against digestive action of pepsin

89
Q

Describe enzyme activation in blood-clotting mechanism

A

Blood clotting is when platelets aggregate at site of tissue damage, releasing clotting factors, such as Factor X

Factor X is an enzyme that is dependant on cofactor vitamin K for activation, and catalyses the conversion of prothrombin into the enzyme thrombin by cleaving specific bonds in the molecule (tertiary structure)

Thrombin is a protease and catalyses conversion of soluble fibrinogen into insoluble fibrin fibres - which together with platelets, form a blood clot

This series of successive enzyme activations in blood clotting is called the coagulation cascade

90
Q

Explain the importance of enzyme activation in controlling blood clotting

A

Enzymes responsible for blood clotting are present as precursors e.g., Factor X,
prothrombin

prevents clotting unless required

91
Q

Describe two ways in which cofactors are necessary for the catalytic role of some enzymes

A

Transfer, atoms / groups, between reactions

form part of active site

92
Q

Explain using an appropriate example of each, how prosthetic groups are different from coenzymes

A

Coenzymes bind loosely to enzymes e.g. NAD

prosthetic groups are a permanent feature of and bind tightly to, proteins / enzymes e.g. iron ion in haemoglobin

93
Q

Using blood clotting as your example, explain the different ways in which enzymes can be activated

A

Presence of cofactor
e.g., vitamin K and Factor X

change in tertiary structure / described
e.g. (activated) factor X catalyses the breaking of bonds in prothrombin
forming thrombin

thrombin catalyses the conversion of fibrinogen to fibrin

94
Q
A

BIOLOGY A LEVEL (24 decks)

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