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IMS Y1 v2 > Topic 4 - Enzymes > Flashcards

Topic 4 - Enzymes Flashcards

1
Q

What is the relevance of enzymes in medicine?

A
  • Defects in enzymes underlie many diseases
  • 30-40% of drug targets are enzymes
  • Enzymes can be drugs themselves
  • Enxyme activity can be diagnostic/prognostic
  • Enzymes are tools in diagnostic/prognostic tests
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2
Q

What are enzymes?

A
  • Biological catalysts of chemical reactions
  • Specific action on particular biochemical compounds (substrates)
  • Nearly all are proteins
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3
Q

What do enzymes do?

A

Increase the rate at which the reaction equilibrium is reached, but do NOT shift the position of equilibrium

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4
Q

How do enzymes increase rate of reaction?

A
  • By providing catalytically competent groups for a specific reaction mechanism
  • By binding substrates such that their orientation is optimised for the reaction
  • By preferentially binding and stabilising the transition state(s) of the reaction
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5
Q

What is the active site of an enzyme?

A

The region of the enzyme at which substrate binding and conversion to product takes place.

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6
Q

What are the features of an active site?

A
  • 3-dimensional space comprising crucial amino acid residues
  • May represent only a small part of the protein structure
  • Binds substrate via multiple weak interactions
  • Provides substrate specificity because of its unique 3D arrangement of atoms
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7
Q

What is trypsin?

A

Proteolytic digestive enzyme
Three key amino acids in active site, but far apart in amino acid sequence
Active site is ‘niche’ for binding substrate

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8
Q

What is the equilibrium constant, K?

A

[A]

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9
Q

What are the three key amino acids making up the active site of trypsin?

A

They are far apart on the ppt chain:
His57
Asp102
Ser195

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10
Q

What is the michaelis-menten model?

A

E+S<>ES>E+P

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11
Q

What is the Michaelis constant, Km?

A

K1

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12
Q

What are the factors affecting enzyme catalysed reaction rates?

A
  • Substrate concentration
  • Enzyme concentration
  • Temperature
  • pH
  • Inhibitors
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13
Q

What is a cofactor?

A

a substance (other than the substrate) whose presence is essential for the activity of an enzyme

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14
Q

What are some major cofactor minerals?

A

Mg2+ and Ca2+ and trace

elements such as Cu2+, Zn2+, Fe2+/3+, Mn2+ and Mo4+

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15
Q

What is the role of metal ions as cofactors?

A
  • Can be part of active site and/or be involved in electrostatic substrate binding (Zn2+ in carbonic anhydrase, Mg2+ in kinases).
  • Can as redox agents (Fe2+/3+ in cytochrome p450s).
  • Can regulate activity of enzymes (Ca2+ in calpain).
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16
Q

What cofactor does carbonic anhydrase require?

A

Zn2+

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17
Q

What is the function of Zn2+ as a cofactor?

A

Zn2+ in carbonic anhydrase active site binds to H2O and activates it for reaction with CO2

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18
Q

What is the role of NADH and FADH2?

A

To carry electrons (Recusing power)

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19
Q

What is the role of Coenzyme A?

A

To carry acetyl units

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20
Q

What is the role of Biotin and Thiamine pyrophosphate?

A

To carry CO2 units bound to carboxylases

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21
Q

Which water soluble enzyme corresponds to coenzymes FAD and FMN?

A

Riboflavin (B2)

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22
Q

Which water soluble enzyme corresponds to coenzymes NAD+ and NADP+?

A

Niacin

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23
Q

Which water soluble enzyme corresponds to coenzyme Thiamine pyrophosphate?

A

Thiamine (B1)

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24
Q

Which water soluble enzyme corresponds to coenzyme Biotinylated carboxylases?

A

Biotin

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25
Q

Which water soluble enzyme corresponds to coenzyme cobamide coenzymes?

A

Cobalamin (B12)

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26
Q

Which water soluble enzyme corresponds to coenzyme tetrahydrofolate?

A

Folic acid

27
Q

Which water soluble enzyme corresponds to coenzyme Pyridoxal phosphate?

A

Pyridoxal (B6)

28
Q

Which water soluble enzyme corresponds to coenzyme A?

A

Pantothenic acid

29
Q

What is pellagra caused by?

A

Niacin/Tryptophan deficiency

30
Q

What is the presentation of pellagra?

A

Dementia, diarrhea and dermatitis

31
Q

What is the ethanol to acetaldehyde reaction catalysed by?

A

Alcohol dehydrogenase

32
Q

What is the acetaldehyde to acetate reaction catalysed by?

A

Acetaldehyde dehydrogenase

33
Q

What is reduction?

A
  • gaining of electrons (hydrogen) by one of the atoms

- loss of oxygen

34
Q

What is Oxidation?

A
  • loss of electrons (hydrogen) by one atom

- gain of oxygen

35
Q

What can Glucose-6-phosphate dehydrogenase (G6DPH) deficiency cause?

A

Metabolic defects!

  • X-linked recessive; most carriers asymptomatic
  • The enzyme produces a large proportion of the body’s NADPH needed to drive biosynthesis of nucleic acids, lipids etc.
36
Q

What symptoms can G6DPH deficiency cause?

A
  • Haemolytic crisis
  • Jaundice
  • Can lead to brain damage (kernicterus) in infants
37
Q

What can trigger a G6DPH deficiency crisis?

A
  • Drugs
  • Foods
  • Infections
38
Q

What does the oxidation of G6P by G6PDH generate?

A

NADPH

39
Q

What is the role of NADPH?

A
  • Fuel for biosynthesis
  • needed to make glutathione, which repairs oxidatively-damaged cell membranes
  • RBCs are dependent on G6DPH to make NADPH
40
Q

What does the pentose phosphate pathway generate?

A
  • Ribose 5-phosphate»> nucleic acids

- NADPH»»Fuel for biosynthesis

41
Q

What is 6-MP?

A
  • a prodrug that is differentially metabolised

- metabolism by TPMT results in inactivation

42
Q

What is the role of Thiopurine methyl transferase (TPMT) in adverse response to cancer chemotherapy?

A

It catalyzes the S-methylation of 6-mercaptopurine (6-MP), azathioprine (AZA), and thioguanine to inactivate these drugs, which are used for treating leukemia and autoimmune diseases. So TPMT deficiency is needed for these drugs to be correctly metabolised.

43
Q

What are the levels of control of enzymes?

A
  1. Inhibition (reversible or irreversible)
  2. Feedback regulation
  3. Covalent modification
  4. Proteolytic activation
44
Q

What are serine protease inhibitors (serpins)?

A

a family of proteins that antagonize the activity of serine proteases

45
Q

What are some examples of serpins?

A
  • Alpha1-antitrypsin (a.k.a. anti-elastase)
  • Pancreatic trypsin inhibitor
  • Antithrombin III
46
Q

What does Alpha1-antitrypsin do?

A

Prevents protease from attacking tissue

47
Q

What does pancreatic trypsin inhibitor do?

A

Controls activity of digestive enzyme

48
Q

What does antithrombin III do?

A

Switches off blood clotting system

49
Q

What are some examples of feedback regulation?

A
  • Energy metabolism pathways
  • NADP+ on G6PDH
  • Purine biosynthesis
  • Amino acid biosynthesis
50
Q

What is protein phosphorylation?

A
  • a universal mechanism of enzyme modulation
  • gamma-phosphate of ATP is transferred to amino acid residues
  • Enzymes are phosphorylated by other enzymes, called protein kinases
  • Phosphate groups are removed by phosphatases
  • Charged group induces conformational change in the enzyme
  • Key processes in cell signaling by growth factors (hormones, cytokines)
51
Q

How is zymogen/pro-enzyme activated?

A

By proteolysis

52
Q

What is proteolysis?

A

Irreversible activation of enzyme after removal of part of peptide chain

53
Q

Where is proteolysis used?

A
  • Digestive enzymes (trypsin, chymotrypsin)

- Blood-clotting system

54
Q

What does proteolysis require?

A

tight control by natural inhibitors (for example antitrypsin, antithrombin III)

55
Q

What does proteolysis prevent?

A
  • enzyme becoming active in the wrong place/wrong time

- eg. premature activation of digestive enzymes in the pancreas

56
Q

What is chymotrypsin?

A
  • Digestive enzyme
  • Mature active protein has 3 polypeptide chains linked by disulfide bonds
  • Zymogen precursor is a single polypeptide
57
Q

What is the connection between chymotrypsin, trypsin and elastase?

A

evolved from common ancestor

58
Q

What is trypsin?

A
  • Made as zymogen called trypsinogen
  • Removal of amino acids 1-6 cause activation - causes small conformational change
  • Initial activation by enteropeptidase, a duodenal enzyme
59
Q

What is the role of proteases in the blood clotting cascade?

A
  • Massive amplification of initial signal
  • Complex interactions in vivo between intrinsic and extrinsic pathways
  • Deficiency in any one factor can result in clotting or bleeding disorders
  • Many blood Factors are serine proteases
60
Q

What is antithrombin III?

A
  • A serine protease inhibitor

- Controls clotting by binding tightly to thrombin and serine protease factors

61
Q

What is the pathway of lysis of blood clots by plasmin?

A
  • TPA adheres to clot and binds plasminogen
  • Serine protease activity of TPA cleaves plasminogen to active plasmin
  • Plasmin digests fibrin clot to small peptides
62
Q

What is TPA?

A

Tissue-type plasminogen activator - plays a role in blood clotting

63
Q

Which drugs would be administered in coronary thrombosis?

A

CLOT BUSTERS//thrombolytics

  • Recombinant TPA
  • Streptokinases (eg. alteplase)

IMS Y1 v2 (14 decks)

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