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Environmental Chemistry > Lecture 5 > Flashcards

Lecture 5 Flashcards

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1
Q

Are xenobiotics often water soluble or not? Are they hydrophilic or hydrophobic?

A

Xenobiotics are not very water soluble. They are often hydrophobic.

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2
Q

Why do you need to metabolise xenobiotics?

A

To make them more water soluble and hydrophilic so it’s easier to get rid of them.

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3
Q

What is the difference between primary metabolism and secondary metabolism? Give examples.

A

Primary metabolism is essential for life while secondary is not.
Primary: citronsyracykeln, metabolism of glucose
Secondary: snake’s venom. It’s important for the snake to produce venom but it will not die immediately if it’s not produced.

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4
Q

Is the metabolism of xenobiotics primary or secondary?

A

It’s often secondary.

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5
Q

What are two other words for metabolism of xenobiotics?

A

Biotransformation and detoxification.

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6
Q

What phases can biotransformation be divided into?

A

Phase I and phase II.

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7
Q

What does phase I and phase II do?

A

It helps increase the water solubility so it gets easier to get rid of the molecule.

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8
Q

What is the problem with excretion of lipophilic compounds?

A

It can’t go out via the kidney.

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9
Q

What do phase I do? What happen with the water solubility of this compound?

A

Add a hydrophilic handle to the lipophilic compound. The water solubility increases.

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10
Q

What do phase II do? What happen with the water solubility?

A

An even larger hydrophilic part is added to the compound with the hydrophilic handle. The water solubility increases even more.

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11
Q

Give some examples of handles used in phase I.

A

Small, hydrophilic polar group. Like hydroxy group, amino group, karboxylsyra.

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12
Q

Give some examples of conjugates used in phase II.

A

Sugar units, they are very hydrophilic.

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13
Q

Do all molecules in the metabolism undergo both phase I and II?

A

No. For some, phase I might be hydrophilic enough. For others, they might already have a handle so they can go directly to phase II.

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14
Q

Place phenol, phenol-O-glucuronide and benzene where they belong in phase I, phase II and end product.

A

Benzene —> Phenol (OH: hydrophilic handle, phenol: major phase I metabolite) —> Phenol-O-glucuronide (major phase II metabolite).

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15
Q

Why is the enzyme cytochrome P-450 important?

A
  1. It is used in the liver to metabolise many xenobiotics.

2. It can catalyse oxidations and reductions (more ox. than red.)

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16
Q

Where is cytochrome P-450 present and what is the environment like?

A

It lives in the ER where it’s hydrophobic.

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17
Q

Why could it be dangerous when we have both ethanol and CHCl3 in our bodies?

A

They are catalysed by the same enzyme, cytochrome P-450, which gives it a stronger toxic effect.

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18
Q

How is the general oxidation performed by cytochrome P-450?

A

R-H + O2 → R-OH + H2O

)NADPH + H+ → NADP+) - coenzyme

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19
Q

Whats the coenzyme of cytochrome P-450?

A

NADPH

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20
Q

Name a example in our body where cytochrome P-450 is important for essential nutrients.

A

It help transform Vitamin D3 into calcitriol which regulates Ca uptake.

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21
Q

In what organ (mainly) can we find cyrochrome P-450?

A

In the liver.

22
Q

What’s the mechanism of cytochrome P-450 to catalyze oxidation reaction? The enzyme has Fe(III) bound to it.

A
  1. The substate comes in (lipophilic association)
    - bind to the lipophilic part of the enzyme.
  2. An electron is added and Fe(III) is reduced to Fe(II)
    - Receive 1 e- from NADPH cytochrome P-450 reductase —> reduce Fe(III) to Fe(II).
  3. O2 binds to the Fe(II).
    - Fe(II) has a good binding force with O2
  4. Fe(II) is oxidized to Fe(V) and the other O is reduced to water
    - Receive 1 e- from NADPH cyrochrome P-450 reductase —> one O is reduced to H2O, the other one is used to oxidize Fe(II) into Fe(V) (very active oxidant).
  5. Fe(V)=O oxidizes R-H
    - Fe(V) the oxidize the substrate to from CH3 to OH and it become Fe(III).
  6. The substrate then become more hydrophilic and is kicked out from the enzyme and the cycle repeats.
23
Q

What is the problem with the cytochrome P-450 cycle?

A

If O2 get an e- from Fe(II) —> O2- gets kicked out because Fe(III) doesn’t have good affinity with oxygen.
O2- —> superoxide anion, ROS: dangerous

24
Q

What does ROS stand for?

A

Reactive Oxygen Species.

25
Q

What are the steps in the generation of ROS? 5 steps, one e- is added in each step.
Which way is the oxidation and which way is the reduction?

A
  1. Dioxygen, O2
  2. Superoxide anion, O2-
  3. Hydrogen peroxide, H2O2
  4. Water and hydroxy radical, H2O + OH*
  5. Water, H2O + H2O (not ROS)

Oxidation: 5 —> 1
Reduction: 1 —> 5
(Increase)

26
Q

What’s the Fenton reaction?

A

H2O2 + Fe(2+) + H+ —> OH* + H2O + Fe(3+)

27
Q

What is the Haber Weiss reaction?

A

O2- + H2O2 —(Fe(3+)) —> OH + OH- + O2

28
Q

What happen if we have a too big iron uptake?

A

It can cause acute iron poisoning.

29
Q

Why are ROS dangerous?

A

Very reactive.

30
Q

Are our cell membranes firm or not?

A

They are not. They need to be “loose” to be able to adapt/let thing in and out.

31
Q

What happen if a cell membrane contain only saturated hydrocarbon tails?

A

The cellmembrane will be too firm.

32
Q

The cellmembrane need unsaturated hydrocarbon tails in order to move. Why is this dangerous in the context of ROS?

A

ROS is highly reactive, especially with organic compounds that contain double bonds.

33
Q

Do radical reactions generate more and more radicals?

A

Yes.

34
Q

What is lipid peroxidation? Does it happen to saturated or unsaturated fatty acids?

A

Is the chain reaction where free radicals steal e- from the lipids in the cell membranes, resulting in cell damage.
It most often affect unsaturated fatty acids since they have double bonds.

35
Q

What kind of molecules are formed from lipid peroxidation?

A

Harmful electrophiles.

36
Q

There are enzymes to degrade ROS. What does Superoxide dismutase (SOD) do? What does catalase do? What does glutathione peroxidase do? What then happen to glutathione peroxidase?

A

SOD: 2 O2*- + 2 H+ —> H2O2 + O2
Catalase: 2 H2O2 —> 2 H2O + O2
Glutathione peroxidase: H2O2 + 2 G-SH —> 2 H2O + G-S-S-G

Later: GS-SG + NADPH + H+ —> 2 G-SH + NADP+

37
Q

What vitamins protects us against radicals?

A

Vitamins C and E.

38
Q

What are the 3 types of phase I reactions?

A
  1. Oxidations
  2. Reductions
  3. Hydrolyses
39
Q

What is the only phase II reaction?

A

Conjugations.

40
Q

What are the 4 types of phase I oxidations?

A
  1. Epoxidation of alkenes and aromatics
  2. Carbon hydroxylation
  3. Heteratom oxidation
  4. Oxidation of alcohols and aldehydes
41
Q

If we see a double bond in this course, what can we assume they can be?

A

Epoxidised!

42
Q

What part of the cytochrome P-450 cycle can be epoxidised (oxidized?)?

A

The part where Fe(V) give away its O, and it become a Fe(III).

43
Q

Are epoxides electrophilic or electrophobic? Is epoxidstion of alkenes metabolic activation or inactivation?

A

Electrophilic.

Metabolic activation, it’s turned into a more toxic form.

44
Q

What is carbon hydroxylation? Is it an oxidation or reduction?

A

It’s where at least one hydrogen is replaced by a hydroxy-group. Oxidation.

45
Q

Where on the molecule does carbon hydroxylation occur?

A
  1. Next to unsaturations

2. Next to heteroatoms, alpha-hydroxylation

46
Q

What is oxidative dealkylation?

A

It’s the end product of a-hydroxylation.

a-hydroxylation: the a-carbon to a heteroatom is hydroxylysed.

47
Q

What is oxidative dehydrohalogenation?

A

???

48
Q

What two compounds can behave like halogens during hydroxylation?

A
  1. Nitriles
  2. Thiols
    ???
49
Q

What is beta-oxidation of fatty acids?

A

The oxidation of C-H on the beta-carbon to a karboxyl-grupp.

50
Q

Does enzymatic degradation of fatty acids belong to the primary or secondary metabolism?

A

Primary metabolism. (Tror det).

Environmental Chemistry (6 decks)

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