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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
Where is G6DPH deficiency high?
Malarial regions
26
Why does G6DPH have high incidence in malarial regions?
Plasmodium parasite depends on intermediate of PPP or metabolite using NADPH from PPP PPP confers resistance to malaria (primaquine anti-malarial drug)
27
What does genetically inherited deficiency in G6PDH result in?
Primaquine-induced haemolytic anaemia Patients who took primaquine anti-malarial drug suffered haemolytic crisis
28
What do RBCs rely on to produce NAPDH?
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
What is NAPDH needed to make?
Glutathione
30
What is function of glutathione>
Repairs oxidatively-damaged cell membranes
31
What is Thiopurine Methyl Transferase (TMPT) important in?
Chemotherapy
32
What is 6-MP? How does it interact with TMPT?
* 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
What is effect of active TMPT enzymes during chemo?
* 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
What is function of enzymes inhibitors?
We don’t want some enzymes to be active all the time so there are several mechanisms in place to switch them off
35
What is function of serine protease inhibitors (serpins)?
o Act as inhibitors with perfect fit to active site of protease o Produced naturally in body & block enzyme activity
36
Are protease enzymes specific or non-specific?
Non-specific
37
What are 3 examples of serpins?
1. Antitrypsin 2. Pancreatic trypsin inhibitor 3. Antithrombin
38
What is function of antitrypsin?
Prevents protease from attacking tissues
39
What is function of pancreatic trypsin inhibitor?
Controls activity of digestive enzyme
40
What is function of antithrombin?
Switches of blood clotting system
41
What is function of feedback regulation?
* Conserves metabolic energy supply of organism | * Prevents build-up of large quantities of unwanted metabolic immediates further along
42
View Regulation of Enzyme notes
For feedback pathways
43
What is phosphorylation catalysed by?
Protein kinases
44
What is dephosphorylation catalysed by?
Phosphatases
45
How is ATP involved in phosphorylation?
ATP used as phosphate donor: -phosphate of ATP is transferred to amino acid residues
46
What does the phosphate induce in the enzyme?
Conformational change and alters active site Phosphorylation of an enzyme can increase or decrease activity
47
What is a zymogen?
An inactive substance which is converted into an enzyme when activated by another enzyme
48
What are activated by proteolysis?
Inactive ‘zymogen’ or ‘pro-enzyme’
49
What is proteolysis?
Irreversible activation of enzyme after removal of part of peptide chain
50
Why does proteolysis require tight control by natural inhibitors (e.g. antitrypsin, antithrombin III)?
Prevents enzyme becoming active in wrong place/wrong time i.e. digesting pancreas
51
What digestive enzymes are produced as zymogens in the pancreas?
Chymotrypsin & trypsin & elastase
52
Where are these zymogens of chymotrypsin & trypsin & elastase then transported?
To the small intestine as their zymogen forms and activated there by cleavage of specific peptide bonds
53
What are chymotrypsin & trypsin & elastase?
Serine proteases
54
What do chymotrypsin & trypsin & elastase all contain in their active site?
Serine amino acid residue
55
What is the zymogen of trypsin?
Trypsinogen
56
How is trypsinogen activated?
It is cleaved and activated by enzyme enteropeptidase: a duodenal enzyme o Only produced in intestine
57
Once activated, what can trypsin do?
Trypsin can cleave and activate further trypsinogen molecules as well as other zymogens (e.g. proelastase --> elastase)
58
What is the zymogen of chymotrypsin?
Chymotrypsinogen (a single polypeptide)
59
How is chymotrypsinogen activated?
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
What is the blood clotting cascade?
Activation of a series of serine protease enzymes form zymogen precursors Massive amplification of initial signal by having proteases cleave other proteases
61
What can a deficiency in any factor lead to in the clotting cascade?
Clotting or bleeding disorders
62
What are many blood factors?
Serine proteases
63
How does antithrombin III control clotting?
By tightly binding to thrombin & serine protease factors
64
What is plasmin?
A serine protease
65
What is the zymogen of plasmin?
Plasminogen
66
What is plasminogen activated by?
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
What is function of plasmin?
Plasmin digests fibrin clot to small peptides that are carried away
68
What is function of administration of recombinant TPA (rTPA) or streptokinase by injecting into circulatory system of patient?
• 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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