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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
What is an example of an Endogenous inhibitor?
Serine protease inhibitors (serpins) Tightly controlled by natural inhibitors
25
What do serpins do?
- 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
What is protein phosphoylation?
Universal mechanism of enzyme modulation - Gamma- phosphate of ATP is transferred to amino acid residues
27
What are enzymes phosphorylated by?
Other enzymes called protein kinases
28
What are phosphate groups removed by?
Phosphatases
29
Where can phosphoylation occur and what does it do to enzyme activity?
- Can occur on many different amino acid residues - Phosphorylation can increase or decrease enzyme activity
30
What is proerolytic activation?
- Inactive zymogen or pro-enzyme is activated by proteolysis - Irreversible activation of enzyme after removal of part of the peptide chain
31
What are examples of Proerolytic activation?
Digestive enzymes (trypsin, chymotrypsin) Blood- clotting system
32
Why does proerolytic activation require tight control?
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
What is Chymotrypsin?
- 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
What are common features of serine proteases?
-Chymotrypsin, trypsin & elastase - Three enzymes evolved from common ancestor, but are functionally distinct
35
What is Trypsin?
- 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
What are blood clotting proteases?
- 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
What are many blood factors?
Serine proteases
38
What does Antithrombin III do?
Inhibits clotting by binding to thrombin/ serine protease factors
39
What do serine proteases do?
The blood clotting system requires the interaction of many serine proteases to cause a fibrin clot formation
40
What are Serine proteases?
Key enzyme in digestion, are activated from inactive precursors (zymogens) by proteolysis

IMS- Strand 3 (3 decks)

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