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BIOL 201 > Lecture 2 > Flashcards

Lecture 2 Flashcards

1
Q

What molecule is at a central point in metabolism?

What can it be converted into, and how?

A

Pyruvate.

Lactate - Reduction.
Acetyl CoA - Oxidative Decarboxylation.
Oxaloacetate - Carboxylation.
Alanine - Transamination.

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2
Q

What is pyruvate synthesised from, and by which process?

A

Glucose, glycolysis.

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3
Q

Where is Acetyl CoA produced? Is it reversible?

A

Mitochondria.

Not reversible.

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4
Q

What are the reactants involved in producing Acetyl CoA?

A

Pyruvate + CoA-SH.

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5
Q

Which enzyme and which coenzyme is used to produce Acetyl CoA?

A 
Pyruvate Dehydrogenase (PDH),
NAD+ -> NADH.
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6
Q

What is the MW of Pyruvate Dehydrogenase?

A

5-10X10^6 Da.

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7
Q

How many separate enzyme proteins does PDH contain? What are they?

A

3: E1, E2, E3.

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8
Q

Where is PDH found in large quantities?

A

Mitochondria of plants and animals.

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9
Q

How many cofactors does PDH require? What type of molecule are most of these? How does this relate to lethargy?

A
  1. Mostly human vitamins.
    Lethargy arises from lack of these vitamins.
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10
Q

What is E1’s cofactor? What’s its association with the enzyme? Is the cofactor sourced from a vitamin?

A

Thiamine pyrophosphate. Bound to enzyme. Cofactor sourced from Thiamine (Vitamin B1).

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11
Q

What are E2’s cofactors? What are their associations with the enzyme? Are these cofactors sourced from a vitamin?

A

Coenzyme A. Free association. Cofactor sourced from Pantothenic Acid (Vitamin B5).

Lipoamide (lipoic acid + lysine residue). Bound to enzyme. Cofactor not sourced from vitamin - non-dietary.

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12
Q

What are E3’s cofactors? What are their associations with the enzyme? Are these cofactors sourced from a vitamin?

A

FAD. Bound to enzyme. Cofactor sourced from Riboflavin (Vitamin B2).

NAD+. Free association. Cofactor sourced from Niacin (Vitamin B3).

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13
Q

What’s very reactive on TPP (Thiamine pyrophosphate)? How does this enable it to react with carbonyl group on pyruvate?

A

The C between the N and S is very reactive. Causes H to readily dissociate as H+, leaving a -ve C ion that can react with carbonyl group of pyruvate.

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14
Q

Why (structurally) does lipoic acid attach to a lysine molecule in protein, forming lipoamine?

A

To form a long extendable, moveable arm.

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15
Q

How does the ring open up in lipoic acid?

A

Two sulphur atoms on it can be reduced during transfer of acetyl group, causing ring to open up,

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16
Q

How large is the long moveable arm in lipoamide?

A

14 Å.

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17
Q

What is E1?

How many subunits is it comprised of?

A

Pyruvate dehydrogenase component.

24 subunits.

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18
Q

What is E2?

How many subunits is it comprised of?

A

Transacetylase core.

8 subunits.

19
Q

What is E3?

How many subunits is it comprised of?

A

Dihydrolipoyl dehydrogenase.

12 subunits.

20
Q

How many distinct domains are there in an E2 subunit? Which component do they interact with?

A

3 distinct domains in one E2 subunit.

Interact with E3 component.

21
Q

What 2 key reactions happen with E1 in pyruvate dehydrogenase?

A

Decarboxylation of Pyruvate.

Transfer of hydroxyethyl group to lipoamide (transacetylation).

22
Q

How does the decarboxylation of pyruvate occur?

A

TPP carbanion spontaneously forms, producing TPP and H+.

Carbanion then adds to carbonyl group of pyruvate, forming hydroxyethyl-TPP, losing CO2 and reacting with H+ in process.

23
Q

How does transacetylation occur in E1?

A

Hydroxyethyl group from hydroxyethyl TPP oxidised to form acetyl group. Reacts with lipoamide to form carbanion of TPP and acetyllipoamide.

24
Q

How is Acetyl CoA formed in E2?

A

Acetyl group from acetyllipoamide transferred to CoA, forming Acetyl CoA and dihydrolipoamide.

25
Q

How is FAD reduced in E3 of PDH?

A

By reaction with Dihydrolipoamide to form Lipoamide and FADH2.
I.e. Regeneration of lipoamide.

26
Q

How is FAD then reoxidised after reduction via dihydrolipoamide?

A

Reacts with NAD+ transferring one hydrogen and offloading the other, forming NADH + FAD + H+.

27
Q

What does the structural integration of three kinds of enzymes in PDH enable?

A

The co-ordinated catalysis of a complex.

28
Q

What 3 advantages do the proximity of the enzyme subunits provide in PDH?

A

Reduces the number of side reactions.
Maximises efficiency.
Maximises rate of reaction.

29
Q

Why is it important that all organisms can control the amount of pyruvate converted into Acetyl CoA? What happens if the concentration is too high?

A

Because it’s an irreversible step, and a commitment to energy production.
High concentrations of reaction products inhibit PDH activity (NADH, Acetyl CoA, ATP).

30
Q

What 3 cofactors can activate the PDH complex?

A

NAD, ADP AMP.

31
Q

What type of reaction is the primary regulator of the PDH complex?
What enzyme performs most of the regulation, and how does it work?

A

Phosphorylation.

PDH kinase, can phosphorylate at 3 serine resides on the E1 subunit, causing loss of enzyme activity or deactivation.

32
Q

When deactivated, what stimulates PDH kinase activity?

A

NADH, ATP, Acetyl CoA.

33
Q

When activated, what inhibits PDH kinase activity?

A

NAD+, ADP/AMP, CoA.

34
Q

What stimulates PDH phosphatase? What does it activate, and where is this important?

A

Elevation of cytosolic Ca2+.

Activates PDH - important in muscles.

35
Q

What enzyme inactivates PDH by phosphorylation?

A

PDH kinase.

36
Q

What enzyme activates PDH by dephosphorylation?

A

PDH phosphatase.

37
Q

Beriberi comes from which language?

A

Sinhalese. :D

38
Q

What causes beriberi?

A

Deficiency of thiamine (vitamin B1).

39
Q

Where is beriberi a serious health problems and why?

A

Far East, as polished rice usually consumed, which removes primary source of thiamine.

40
Q

What common condition does beriberi sometimes manifest itself in?

A

Alcoholism.

41
Q

What type of disorder is beriberi, and why?

A

Neurological, because glucose is the primary source of energy for the CNS, as fats can’t be used.

42
Q

What are you likely to find high levels of in the blood of a patient with beriberi?

A

Pyruvate and lactic acid.

43
Q

What type of poisoning has similar symptoms to beriberi? Why?

A

Mercury and arsenite, as arsenite can react with dihydrolipoamide from E2 of PDH, producing an arsenite chelate on the enzyme.

44
Q

How does BAL (British anti-lewisite) cure arsenite poisoning?

A

Binds arsenite chelate on enzyme, and is then excreted, restoring normal enzyme.

BIOL 201 (3 decks)

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