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Yr 1 - Proteins & Enzymes > Enzyme Function > Flashcards

Enzyme Function Flashcards

1
Q

What are cofactors essential for?

A

Enzyme action

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2
Q

What metal ions are major minerals?

A

Mg2+ and Ca2+

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3
Q

Which metal ions act as essential components in active sites and/or involved in electrostatic substrate binding?

A

Zn2+ in carbonic anhydrase

Mg2+ in kinases

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4
Q

What metal ions can act as redox agents?

A

Fe2+/3+ in cytochrome P450s (liver)

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5
Q

What is function of Ca2+ in calpain?

A

Regulate activity of enzymes

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6
Q

What cofactor does carbonic anhydrase need? How does this work?

A

Zn2+

  • Zn2+ in carbonic anhydrase active site binds to H20
  • This activates it for reaction with C02
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7
Q

What cofactor do kinases need?

A

Mg2+

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8
Q

What are coenzymes?

A

Many water-soluble vitamins consumed in diet are (part of) essential coenzymes

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9
Q

What do coenzymes function as?

A

Carriers of reaction components

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10
Q

How do NADH and FADH2 act as coenzymes?

A

Carry electrons (‘reducing power’)

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11
Q

How does coenzyme A act as a coenzyme?

A

Carries acyl units

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12
Q

How do biotin and thiamine pyrophosphate act as coenzymes?

A

Carry CO2 units

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13
Q

What can a B vitamin deficiency lead to?

A

Anaemia

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14
Q

What are NADH and NAPDH involved in?

A

Energy metabolism & biosynthetic reactions individually

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15
Q

What are the niacin (B3) (nicotinic acid) coenzymes?

A

NADH and NAPDH

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16
Q

What does a Niacin deficiency lead to?

A

Pellagra

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17
Q

What is the presentation of Pellagra?

A

Dementia, diarrhoea

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18
Q

What are the causes of Pellagra?

A

Poor diet, alcoholism

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19
Q

What is the most common enzyme deficiency?

A

Glucose-6-phospate dehydrogenase (G6PDH) deficiency

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20
Q

How is G6PDH deficiency acquired?

A

X-linked recessive (genetically inherited): most carriers asymptomatic until prescribed certain drugs then problems found

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21
Q

What does G6PDH produce?

A
  • Enzyme produces large proportion of body’s NADPH needed to drive biosynthesis of nucleic acids, lipids etc
  • Oxidation of G6P by G6PDH generates NADPH
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22
Q

What 2 pathways can G6P go down?

A

Glycolysis or Pentose Phosphate Pathway

Glucose –> G6P –> ?

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23
Q

What does the pentose phosphate pathway produce?

A

Makes ribose-5-phosphate which are required for active growth

Also makes NAPDH

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24
Q

What is NAPDH essential for?

A

RBCs

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25
Q

Where is G6DPH deficiency high?

A

Malarial regions

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26
Q

Why does G6DPH have high incidence in malarial regions?

A

Plasmodium parasite depends on intermediate of PPP or metabolite using NADPH from PPP

PPP confers resistance to malaria (primaquine anti-malarial drug)

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27
Q

What does genetically inherited deficiency in G6PDH result in?

A

Primaquine-induced haemolytic anaemia

Patients who took primaquine anti-malarial drug suffered haemolytic crisis

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28
Q

What do RBCs rely on to produce NAPDH?

A

Red blood cells lack mitochondria so rely entirely on PPP to produce NADPH
o Deficient patients tend to have low levels of NADPH in RBCs
• Not always a problem as sufficient ‘reducing power’ to prevent damage to RBCs by strongly oxidising free radicals

29
Q

What is NAPDH needed to make?

A

Glutathione

30
Q

What is function of glutathione>

A

Repairs oxidatively-damaged cell membranes

31
Q

What is Thiopurine Methyl Transferase (TMPT) important in?

A

Chemotherapy

32
Q

What is 6-MP? How does it interact with TMPT?

A
  • 6-MP is a prodrug (i.e. must be metabolised before it becomes active) that is differentially metabolised
  • Metabolism of 6-MP by TPMT results in 6-methyl MP (inactivation)
33
Q

What is effect of active TMPT enzymes during chemo?

A
  • TPMT less active them chemo will work better –> more of active drug
  • However, if too little TPMT then you will start to kill off healthy cells
34
Q

What is function of enzymes inhibitors?

A

We don’t want some enzymes to be active all the time so there are several mechanisms in place to switch them off

35
Q

What is function of serine protease inhibitors (serpins)?

A

o Act as inhibitors with perfect fit to active site of protease
o Produced naturally in body & block enzyme activity

36
Q

Are protease enzymes specific or non-specific?

A

Non-specific

37
Q

What are 3 examples of serpins?

A
  1. Antitrypsin
  2. Pancreatic trypsin inhibitor
  3. Antithrombin
38
Q

What is function of antitrypsin?

A

Prevents protease from attacking tissues

39
Q

What is function of pancreatic trypsin inhibitor?

A

Controls activity of digestive enzyme

40
Q

What is function of antithrombin?

A

Switches of blood clotting system

41
Q

What is function of feedback regulation?

A
  • Conserves metabolic energy supply of organism

* Prevents build-up of large quantities of unwanted metabolic immediates further along

42
Q

View Regulation of Enzyme notes

A

For feedback pathways

43
Q

What is phosphorylation catalysed by?

A

Protein kinases

44
Q

What is dephosphorylation catalysed by?

A

Phosphatases

45
Q

How is ATP involved in phosphorylation?

A

ATP used as phosphate donor: -phosphate of ATP is transferred to amino acid residues

46
Q

What does the phosphate induce in the enzyme?

A

Conformational change and alters active site

Phosphorylation of an enzyme can increase or decrease activity

47
Q

What is a zymogen?

A

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

48
Q

What are activated by proteolysis?

A

Inactive ‘zymogen’ or ‘pro-enzyme’

49
Q

What is proteolysis?

A

Irreversible activation of enzyme after removal of part of peptide chain

50
Q

Why does proteolysis require tight control by natural inhibitors (e.g. antitrypsin, antithrombin III)?

A

Prevents enzyme becoming active in wrong place/wrong time i.e. digesting pancreas

51
Q

What digestive enzymes are produced as zymogens in the pancreas?

A

Chymotrypsin & trypsin & elastase

52
Q

Where are these zymogens of chymotrypsin & trypsin & elastase then transported?

A

To the small intestine as their zymogen forms and activated there by cleavage of specific peptide bonds

53
Q

What are chymotrypsin & trypsin & elastase?

A

Serine proteases

54
Q

What do chymotrypsin & trypsin & elastase all contain in their active site?

A

Serine amino acid residue

55
Q

What is the zymogen of trypsin?

A

Trypsinogen

56
Q

How is trypsinogen activated?

A

It is cleaved and activated by enzyme enteropeptidase: a duodenal enzyme
o Only produced in intestine

57
Q

Once activated, what can trypsin do?

A

Trypsin can cleave and activate further trypsinogen molecules as well as other zymogens (e.g. proelastase –> elastase)

58
Q

What is the zymogen of chymotrypsin?

A

Chymotrypsinogen (a single polypeptide)

59
Q

How is chymotrypsinogen activated?

A
  1. Chymotrypsin is secreted into duodenum
  2. Encounters active trypsin
  3. Trypsin cleaves inactive chymotrypsinogen close to N terminal: giving partially active form
  4. Active chymotrypsin already in duodenum cuts at 2nd site: giving fully active form
60
Q

What is the blood clotting cascade?

A

Activation of a series of serine protease enzymes form zymogen precursors

Massive amplification of initial signal by having proteases cleave other proteases

61
Q

What can a deficiency in any factor lead to in the clotting cascade?

A

Clotting or bleeding disorders

62
Q

What are many blood factors?

A

Serine proteases

63
Q

How does antithrombin III control clotting?

A

By tightly binding to thrombin & serine protease factors

64
Q

What is plasmin?

A

A serine protease

65
Q

What is the zymogen of plasmin?

A

Plasminogen

66
Q

What is plasminogen activated by?

A

o Activated by TPA
 TPA adheres to clot & binds plasminogen: concentrates plasmin activity to right place
 Serine protease activity of TPA cleaves plasminogen to active plasmin

67
Q

What is function of plasmin?

A

Plasmin digests fibrin clot to small peptides that are carried away

68
Q

What is function of administration of recombinant TPA (rTPA) or streptokinase by injecting into circulatory system of patient?

A

• Can significantly increase chances of surviving coronary thrombosis
o A blockage of flow of blood to heart caused by blood clot in coronary artery
• Rapidly restoring circulation to heart muscle buy removing blockage
o rTPA & Alteplase: referred to as ‘clot-buster’ or ‘thrombolytics’

Yr 1 - Proteins & Enzymes (8 decks)

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