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IMS- Strand 3 > Regulation of enzyme activity > Flashcards

Regulation of enzyme activity Flashcards

1
Q

What factors affect enzyme activity?

A

Temperature
pH

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2
Q

What is the importance of metal ions as cofactors?

A
  • Includes major minerals such as Mg2+ and Ca2+ and trace elements such as Cu2+
  • Metal ions can be part of active site and/ or be involved in electrostatic substrate binding
  • Metal ions may act as redox agents
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3
Q

What are cofactors?

A

Something the enzyme requires to function

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4
Q

What does Zn2+ do as a cofactor?

A

Zn2+ in carbonic anhydrase active sites binds to H20 and activates it for reaction with CO2

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5
Q

What do coenzymes do?

A
  • Many water soluble vitamins are (part of) essential coenzymes
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6
Q

What are 3 examples of Coenzymes?

A
  • Coenzymes function as carriers of reaction components
  • Coenzyme A carries acyl units
  • NAD(P)H and FAD(P)H2 carry electons (reducing power)
  • Biotin and thiamine pyrophosphate carry CO2 units (bound to carboxylases)
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7
Q

What do vitamin B3 based coenzymes do?

A

Pellegra, caused by niacin/ tryptophan deficiency presents as: dementia, diarrhea & dermatitis

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8
Q

How does the body metabolise alcohol?

A

NAD+ redox reactions

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9
Q

What is the mechanism for the metabolism of alcohol?

A

Ethanol is reduced using Alcohol dehydrogenase & NAD+ to form Acetaldehyde which is further reduced to form Acetate using NAD+ & acetaldehyde dehydrogenase

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10
Q

What happens in chronic alcoholism?

A
  • Often accompanied by malnutrition and gastrointestinal problems
  • Alcohol metabolism needs NAD+ ( & therefore niacin)
  • Alcohol inhibits conversion of tryptophan to niacin
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11
Q

What is G6PDH?

A

Glucose- 6- phosphate dehydrogenase

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12
Q

What does a G6PDH deficiency cause?

A

metabolic defects

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13
Q

What is G6PDH deficiency?

A
  • Most common enzyme deficiency
  • X- linked recessive most carriers are asymptomatic
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14
Q

What does the G6PDH enzyme do?

A
  • The enzyme produces a large proportion of the body’s NADPH needed to drive biosynthesis of nucleic acids, lipids etc
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15
Q

When symptomatic of G6PDH deficiency what symptoms are there?

A

Haemolytic crises
Jaundice (can lead to brain damage in infants)

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16
Q

What can a haemolytic crisis be caused by?

A

drugs, foods and infections

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17
Q

What is the pentose phosphate pathway?

A

Oxidation of G6P by G6PDH generates NADPH

18
Q

What does a genetically inherited deficiency in G6PDH cause?

A

(X linked, high incidence in malarial regions)
Results in
Primaquine- induced haemolytic anaemia

19
Q

What is Primaquine induced anaemia?

A

Glutathione repairs oxidatively- damaged cell membranes
NADPH is need too for recycling of glutathione
RBC don’t have mitochondria so depend on G6PDH to make NADPH
No NADPH= build up of hydroperoxides which damages membranes

20
Q

What is TPMT?

A

Thiopurine methyl transferase

21
Q

What is TPMT deficiency?

A

an adverse response to cancer chemotherapy

22
Q

What is 6-MP?

A

Is a prodrug that is differentially metabolised
Metabolism by TPMT results in inactivation

23
Q

What does the amount of TPMT affect?

A

The lower the amount of TPMT activity the greater sensitivity to 6-MP so lower dosage

24
Q

What are the 4 levels of enzyme control?

A
  1. Inhibition (reversible or irreversible)
  2. Feedback regulation
  3. Covalent modification (for example phosphorylation)
  4. Proteolytic activation
25
Q

What is an example of an Endogenous inhibitor?

A

Serine protease inhibitors (serpins)
Tightly controlled by natural inhibitors

25
Q

What do serpins do?

A
  • A1- antitrypsin (aka anti- elastase)= prevents protease from attacking tissue
  • Pancreatic trypsin inhibitor= controls activity of digestive enzyme
  • antithrombin III= switches off blood clotting system
26
Q

What is protein phosphoylation?

A

Universal mechanism of enzyme modulation
- Gamma- phosphate of ATP is transferred to amino acid residues

27
Q

What are enzymes phosphorylated by?

A

Other enzymes called protein kinases

28
Q

What are phosphate groups removed by?

A

Phosphatases

29
Q

Where can phosphoylation occur and what does it do to enzyme activity?

A
  • Can occur on many different amino acid residues
  • Phosphorylation can increase or decrease enzyme activity
30
Q

What is proerolytic activation?

A
  • Inactive zymogen or pro-enzyme is activated by proteolysis
  • Irreversible activation of enzyme after removal of part of the peptide chain
31
Q

What are examples of Proerolytic activation?

A

Digestive enzymes (trypsin, chymotrypsin)
Blood- clotting system

32
Q

Why does proerolytic activation require tight control?

A

Requires tight control by natural inhibitors as it prevents enzymes becoming active in the wrong place/ time
e.g. premature activation of digestive enzymes in the a
pancreas

33
Q

What is Chymotrypsin?

A
  • Digestive enzyme
  • zymogen precursor in a single polypeptide
  • Mature active protein has 3 polypeptide chains linked by disulfide bonds
  • Active site contains catalytic triad of aspartate, histidine and serine
34
Q

What are common features of serine proteases?

A

-Chymotrypsin, trypsin & elastase
- Three enzymes evolved from common ancestor, but are functionally distinct

35
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
36
Q

What are blood clotting proteases?

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
37
Q

What are many blood factors?

A

Serine proteases

38
Q

What does Antithrombin III do?

A

Inhibits clotting by binding to thrombin/ serine protease factors

39
Q

What do serine proteases do?

A

The blood clotting system requires the interaction of many serine proteases to cause a fibrin clot formation

40
Q

What are Serine proteases?

A

Key enzyme in digestion, are activated from inactive precursors (zymogens) by proteolysis

IMS- Strand 3 (3 decks)

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