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Biology (Semester 1) > L11 & 12: Enzymes > Flashcards

L11 & 12: Enzymes Flashcards

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1
Q

What percentage of human genes code for enzymes?

A

25%

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2
Q

Are enzymes used up in the reaction?

A

No

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3
Q

What are enzymes made from?

A

Protein

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4
Q

What does a proteolytic enzyme do?

A

Breaks down proteins

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5
Q

What is papain? What does it do?

A

Enzyme found in papaya plants. Used to break peptide bonds - specifically used to tenderise meat

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6
Q

What is trypsin? What does it do?

A

Digestive enzyme that only splits bonds between lysine and arginine residues

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7
Q

What is thrombin? What does it do?

A

Activates the process of clotting by cleaving fibrinogen

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8
Q

What is the active site formed from?

A

Specific amino acids. They create charged regions that only appropriate chemical groups can bind to.

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9
Q

True or false: Enzymes are slowly used up in the reactions they govern, so must be replaced by the cell.

A

False

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10
Q

True or false: Enzymes are coded for by only a few highly regulated genes.

A

False. They are coded for by 25% of all our genes

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11
Q

True or false: Enzymes are mainly produced by ribosomes.

A

True

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12
Q

True or false: Most enzymes can catalyse 2 or 3 related reactions.

A

False

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13
Q

True or false: Thrombin is a relatively non-specific protease.

A

False

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14
Q

True or false: Cyclins are enzymes which control the cell cycle.

A

False

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15
Q

True or false: Changing the active site often renders the enzyme non-functional.

A

True

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16
Q

True or false: Substrates bind to the active site of the enzyme.

A

True

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17
Q

True or false: Enzyme-substrate complexes are always formed during biological catalysis.

A

True

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18
Q

True or false: Amino acids away from the active site can control binding specificity.

A

True

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19
Q

What are coenzymes and cofactors?

A

Non-protein molecules that can alter the shape of the active site by binding to the enzyme away from its active site

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20
Q

What is an apoenzyme?

A

An enzyme without its cofactor

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21
Q

What is a holoenzyme?

A

An enzyme that has its cofactor

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22
Q

Describe cofactors

A

Simple inorganic ion that causes the enzyme to fold and change shape, enhancing the charge to improve substrate binding.

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23
Q

Give an example of a cofactor and its relevant enzyme

A

Chloride ions and amylase

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24
Q

Describe coenzymes

A

Small organic molecules that attach to activate the enzyme and detach when reaction completed to deactivate the enzyme. Often vitamins (e.g Niacin, riboflavin). They act as transporters of chemical groups from one reactant to another.

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25
Q

What are isoenzymes?

A

Enzymes that are chemically different, but catalyse the same reaction

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26
Q

Why are isozymes important?

A

They can be activated under different conditions to fine-tune metabolic processes. They may display different kinetic parameters (e.g Km/Vmax) or regulatory properties

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27
Q

What are the 6 classes of enzyme?

A 
Oxidoreductases
Transferases
Hydrolases
Lyases
Isomerases
Ligases
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28
Q

What is the general role of oxidoreductases?

A

Catalyse redox reactions

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29
Q

What is the general role of the transferases?

A

Move a functional group from one molecule to another

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30
Q

Kinases are examples of what class of enzyme?

A

Transferase

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31
Q

Generate a double bond through an elimination reaction

A

Lyases

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32
Q

What is the general role of the lyases?

A

Break things down and form double bonds

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33
Q

What is the general role of the isomerases?

A

Catalyse structural changes within a molecule. Nothing gained, nothing lost.

34
Q

What is the general role of the ligases?

A

Catalyse ligation (joining two things together). Usually coupled with the hydrolysis of a disphosphate bond (e.g. ATP)

35
Q

What is the general role of the hydrolases?

A

Catalyse hydrolysis reactions

36
Q

What is an exo-hydrolase?

A

Enzyme that cleaves of individual monomers

37
Q

What is an endo-hydrolase?

A

Enzyme that cuts through the middle of the chain. Doesn’t create monomers.

38
Q

Which hydrolase breaks down proteins by severing peptide bonds between amino acids?

A

Proteases/peptidases

39
Q

Which hydrolase cleaves ester bonds to form fatty acids and glycerol?

A

Lipase

40
Q

Which hydrolase cleaves phosphodiester bonds? What is produced as a result?

A

Nucleases. They form nucleotides from nucleic acids.

41
Q

How does substrate concentration affect enzyme activity?

A

Increases until saturation point

42
Q

How does enzyme concentration affect enzyme activity?

A

Increases until saturation point

43
Q

How does temperature affect enzyme activity?

A

Cold: reduced kinetic energy reduces enzyme activity. Reversible.

Hot: Increases activity until excessive heat denatures enzymes. Irreversible.

44
Q

pH

A

Too acid or too alkali will inhibit or denature enzymes

45
Q

What units are used to express enzyme activity?

A

International Units (IU)

1IU = 1 micromole/min

46
Q

Why are enzyme velocities measured at time 0, or before 10% of substrate is used up?

A

Measures rate of reaction before feedback inhibition or reversible reactions kick in

47
Q

What is Michaelis-Menten Enzyme Kinetics?

A

Study of the rate of an enzyme-controlled reaction

48
Q

What is Vmax?

A

The maximum rate of reaction controlled by enzymes

49
Q

What is Km?

A

The concentration of substrate when the reaction rate is half of Vmax

50
Q

Describe the Km and Vmax of a fast, efficient specific enzyme

A

Low Km; high Vmax

51
Q

What value is commonly used to distinguish isoenzymes from each other?

A

Km

52
Q

Use Hexokinase and Glucokinase to demonstrate the importance of Km

A

Hexokinase is found in liver cells. Switched on at low gluc levels (low Km) so used for general storage of glucose. Glucokinase is in the pancreas, has high Km. Only activates when gluc levels are high.

53
Q

What does ACE Inhibitor stand for?

A

Angiotensin-converting enzyme inhibitor

54
Q

What is Phosphodiesterase Inhibitor more commonly known as?

A

Viagra

55
Q

What are the 5 types of enzyme inhibitor?

A
  1. Reversible
  2. Irreversible
  3. Uncompetitive
  4. End Product
  5. Zymogens
56
Q

What are the 2 subtypes of reversible inhibitor?

A

Competitive and non-competitive (allosteric)

57
Q

How do competitive inhibitors work?

A

Bind to active site to prevent the substrate binding. Only last a moment, and then the enzyme is free to bind to another substrate or competitive inhibitor

58
Q

Give an example of a competitive inhibitor.

A

Disulfiram (Antabuse) - used to treat alcoholism as it causes unpleasant side-effects of nausea and vomiting.

Ethanol - used to treat methanol poisoning as it competes, slowing the production of formaldehyde.

59
Q

What type of inhibitor is disulfiram? Which enzyme does it inhibit?

A

Competitive. Inhibits aldehyde dehydrogenase.

60
Q

What type of inhibitor is ethanol? Which enzyme does it inhibit?

A

Competitive. Inhibits alcohol dehydrogenase.

61
Q

How does non-competitive (allosteric) inhibition work?

A

An allosteric inhibitor binds to the allosteric site on an enzyme, distorting the shape of the active site to prevent substrate from binding to it.

62
Q

Give an example of a non-competitive inhibitor.

A

Nifedipine - blocks calcium uptake into cardiac cells by changing the shape of the calcium channel. Treats angina and hypertension.

63
Q

What type of inhibitor is Nifedipine? Which enzyme does it inhibit?

A

Non-competitive. Inhibits Calcium-dependent ATPase

64
Q

What effect do competitive inhibitors have on Vmax and Km?

A

Vmax is unaffected; Km is increased

65
Q

What effect do non-competitive inhibitors have on Vmax and Km?

A

Vmax is reduced; Km is unaffected

66
Q

How do irreversible inhibitors work?

A

Bind covalently to enzyme, permanently rendering them unusable

67
Q

Give an example of an irreversible inhibitor.

A

Sarin binds to a serine residue in acetylcholinesterase, preventing nerve impulse transmission.

Aspirin bind to prostaglandin H2 synthase, reducing synthesis of inflammatory signals

68
Q

How does uncompetitive inhibition work?

A

When a substrate binds to the enzyme, an inhibitor also binds, away from the active site. This prevents the enzyme-substrate complex from becoming a product.

69
Q

Give an example of uncompetitive inhibition.

A

Lithium treats manic-depressive psychosis

70
Q

What type of inhibitor is Lithium? Which enzyme does it inhibit?

A

Uncompetitive. Inhibits inositol monophosphatase

71
Q

How does end-product (feedback) inhibition work?

A

The end product of a process is also the inhibitor. When there is lots of end product, the enzymes are temporarily stopped. As the level of end product decreases, the enzyme activity resumes. This is an important method of self-regulation in the body.

72
Q

What does the inhibitor often bind to during feedback inhibition?

A

Allosteric site of the enzyme being inhibited

73
Q

Consider the biochemical pathway used to synthesize the amino acid proline. A high increase in the level of proline will most likely lead to…

A) a decrease in proline production.

B) further increase in proline production.

C) no change in the rate of proline production.

D) increased breakdown of proline.

A

A) A decrease in proline production

74
Q

Which of these is a competitive inhibitor?

A) sarin

B) lithium

C) ethanol

D) Aspirin

A

C) Ethanol

75
Q

Competitive inhibitors

A) Decrease Km, do not affect Vmax

B) Do not affect Km, increase Vmax

C) Increase Km, increase Vmax

D) Increase Km, do not affect Vmax

A

D) Increase Km, do not effect Vmax

76
Q

Nifedipine is an anti-angina drug. It works by:

A) Covalently modifying prostaglandin H2 synthase

B) Inhibits the aldehyde oxidase

C) Inhibits Ca2+ dependent ATPase

D) Inhibits inositol monophosphatase

A

C) Inhibits Ca2+ dependent ATPase

77
Q

What is a zymogen?

A

An enzyme with a ‘shield’ that blocks the active site. The shield is known as a pro-sequence and must be cleaved off to allow access to the active site. It is cleaved off at the activation site (not to be confused with the active site…)

78
Q

In addition to inhibitors, what three other methods regulate enzyme activity?

A
  1. Gene expression
  2. Phosphorylation
  3. Proteolysis
79
Q

What does ELISA stand for?

A

Enzyme-linked immunosorbent assay

80
Q

What is ELISA used to detect? (5 examples)

A
  1. Mycobacterium antibodies in TB
  2. Hep-B markers in serum
  3. Enterotoxin of E. Coli in faeces
  4. HIV antibodies in blood samples
  5. Hormone levels
81
Q

Which enzyme is most commonly used in ELISA?

A

Horseradish Peroxidase (HRP)

82
Q

What are the steps of ELISA?

A
  1. Primary antibody is coated on 96-well plate
  2. Add patient sample
  3. Antigens in patient sample bind to antibody
  4. Wash to remove excess/unbound antigen
  5. Add secondary antibody, bound to HRP
  6. Wash to remove excess/unbound antibody
  7. Add substrate and observe colour intensity

Biology (Semester 1) (10 decks)

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