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Biochem > Electron Transport Chain > Flashcards

Electron Transport Chain Flashcards

1
Q

ETC is essentially chain of

A

Redox reactions

Goal: To reduce molecular oxygen

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2
Q

Flow of electrons (overall)

A

NADH —> Complex 1 —> CoQ —> Complex III —> Cyt c —> Complex IV —> O2

FADH2 also donates its electrons to Complex II which donates to CoQ

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3
Q

Synthesis of ATP is coupled to

A

Electron transfer

No electron transfer = no proton gradient = no energy = no ATP synthesis

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4
Q

Electrons move in one direction because? (2)

Trend?

A
  1. Of changes in standard reduction potential.
    — As you move down the chain, each e- acceptor is better than the previous as indicated by their more positive standard reduction potentials.
  2. Successive transfer of electrons are exergonic.
    — Standard free energy change is related to the change in reduction potential
    —For every 2 electrons passed —> 220 kJ/mol energy generated
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5
Q

Electron transfer potential of NADH and FADH2 is converted to __________ of _______

A

High phosphoryl transfer potential of ATP

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6
Q

Oxidation-reduction reactions must _______

A

Occur together.

One molecule is oxidized —> something else is reduced

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7
Q

Redox reactions occur in “ ________”

A

Two half reactions

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8
Q

Ultimate electron donor =

A

Carbon source

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9
Q

Ultimate electron acceptor =

A

O2

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10
Q

A more negative standard reduction potential means _______

A

Better electron DONOR

Ex. NADH is better than FADH2

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11
Q

A more positive standard reduction potential means ____

A

Better electron ACCEPTOR

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12
Q

Each complex of the ETC contains _____

A

Fe

  • coordinated because very reactive
  • good in redox reactions
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13
Q

All prosthetic groups accept and pass _____ electron at a time except _______ which can _________

A

All prosthetic groups accept and pass 1 electron at a time except FMN which can accept 2 electrons (still passes 1)

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14
Q

4 Main Molecules in ETC

A
  1. Flavoproteins
  2. Cytochromes
  3. Iron-Sulfur proteins
  4. Protein bound copper
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15
Q

Prosthetic groups do the ___________

A

Chemistry

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16
Q

Flavoproteins

2

A

FMN and FAD

  • tightly bound
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17
Q

FMN

A

Flavoproteins - Prosthetic group in Complex I

Need b/c NADH is carrying 2 e- and 1 H+ and can accept 2 electrons

Still only passes one electron, though

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18
Q

FAD

A

Flavoprotein- Prosthetic group on Complex II

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19
Q

Cytochromes (b,c,c1, a,a3)

A

Contain heme (Fe2+,Fe3+) prosthetic groups

Complexes III and IV

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20
Q

All heme prosthetic groups:

A

Absorb light around 415 nm

Just the substitutions on the protoporphyrin ring differ leading to different cytochromes

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21
Q

Iron Sulfur Proteins

A

Prosthetic groups in complexes I, II, III
- Has one or more Fe-S clusters

Fe2+ , Fe3+

cysteine groups

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22
Q

Protein bound copper

A

Prosthetic groups in complex IV only

Cu2+ and Cu+

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23
Q

Coenzyme Q / Ubiquinone important characteristics

A
  • A lipid
  • Mobile electron carrier
  • Has an isoprenoid hydrophobic tail
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24
Q

Quinone functional group of CoQ

A

Undergoes “redox cycling” - can continuously cycle from oxidized to reduced state as radicals in the process

Therefore, CoQ is a source of O2 free radicals in the ETC

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25
Q

How can CoQ be a source of O2 free radicals?

A

Quinone functional group:

Accept 1 e- and 1 H+ —> form semi quinone intermediate. If this loses the H+ it forms the semi quinone radical which is bad

But, if followed by another acception of 1 e- and 1 H+ —> form reduced CoQ which is fine

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26
Q

Isoprene functional unit

A
  • A 5-C repeating unit that produces a LONG carbon hydrophobic tail
  • Allows molecule to move laterally in the membrane
  • Made in biosynthesis pathway for cholesterol
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27
Q

Isoprene is made in the biosynthetic pathway for _______________.

A

Cholesterol

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28
Q

Patients on statin drugs (to reduce high cholesterol) often experience muscle weakness, why?

A

Statin drug inhibits cholesterol synthesis therefore not making isoprene units —> block availability of isoprene for CoQ

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29
Q

CoQ function

A

Accepts electrons from complex I and complex II —> transfer to complex III

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30
Q

Further down chain = ____________ electron acceptor

Why?

A

BETTER

More positive standard reduction potential

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31
Q

Complex I location

A

Part of the complex is embedded in the inner mitochondrial membrane
— each of the helices contributes to action of proton pump

The rest of the complex protruding into the matrix portion.
— FMN located here

32
Q

Complex I functions as _____

How can it do this?

A

A proton pump with 3 channels

  • As the electrons move down the prosthetic groups, protons are pumped from the matrix into the inter membrane space
  • Can do this because the of the amino acid composition of the helices —> Charged amino acids can change their charge depending on whether they are binding to a proton or releasing it
33
Q

In Complex I, _________ and _________ happen together.

A

Electron flow and proton pumping

34
Q

Explain electron transfer in complex I

A

NADH donates 2 electrons to FMN —> FMN passes one electron at a time to various Fe-S centers —> electrons continue to move and as they move protons are pumped into the IMS space —> two additional protons from the matrix side reduce CoQ that is embedded in the meme brand

35
Q

2 main things at play in complex I

A
  1. Exergonic nature of free energy change as electrons are passed
  2. Proton pumping - beginning of generation of proton gradient
36
Q

Proton gradient contains _____ called ______

Purpose?

A

Energy. Called proton motive force

Powers ATP synthase

37
Q

Complex I can be a source of ________ that are associated with

A

reaction oxygen species ; neurodegenerative diseases

38
Q

Complex II structure & location & groups

A
  • Includes Succinate dehydrogenase (part of TCA cycle)
  • Has flavoprotein (FAD) and Fe-S center
  • Located in inner mitochondrial membrane
39
Q

What happens in complex II?

A

FAD accepts electrons from FADH2 —> prosthetic groups —> CoQ

Reaction is exergonic

40
Q

CoQ gets electrons from ? And take them to?

A

Complexes I and II

Takes to Complex III

41
Q

What is unique about complex II?

A

NO proton pumping!!

Therefore, does not contribute to proton motive force.

42
Q

Do you get more protons from NADH or FADH2? Why?

A

NADH. Because complex II does not do proton pumping.

43
Q

Complex III- prosthetic groups

A
  • Cytochrome bc1 and Fe-S center
44
Q

What happens at complex III?

A

CoQ passes its electrons to cytochrome c

Net 2 H+ pumped into IMS

45
Q

Cytochrome c properties

A
  • Small protein on outer side of inner membrane
  • Water soluble
  • Can move laterally within membrane
  • Carries electrons to complex IV
46
Q

Complex 4 prosthetic groups

A
  • Cytochome a and a3

- Heme a3 & CuB form the active center that reduces oxygen

47
Q

What happens at complex IV ***?

A
  1. Two molecules of cytochome c sequentially transfer electrons to reduce CuB and heme a3
  2. O2 enters and forms a peroxide bridge between the Fe and Cu
  3. 2 additional cytochrome c come and transfer 2 e-
  4. Cleave the peroxide bridge
  5. 2 H+ from matrix added to the oxygens —> Fe binds one, Cu binds the other, 1 proton attached to O in each case
  6. 2 more H+ from matrix
  7. Release of H2O
48
Q

How many chemical protons are from pumped in matrix and what is their purpose?

A

Reduce O2 —> H2O

49
Q

Complex IV is the site of _______poisoning

A

CN and CO

50
Q

Totals of H+ at each complex

A

Complex I = 4

Complex II = 0

Complex III = 2

Complex IV = 4

51
Q

_____ H+ per 2 e- being passed

A

10

52
Q

Significance of respiratory inhibitors (2)

A
  1. Blocks the transfer of electrons (therefore ATP synthase activity)
  2. Allowed the order of complexes to be determined
53
Q

Rotenone and Amytal

A
  • Inhibit complex I
  • Electrons don’t move to CoQ —> NADH builds up —> TCA cycle slows down because NADH is negative allosteric modifier of isocitrate dehydrogenase
54
Q

Antimycin A

A

Inhibits complex III

55
Q

Cyanide, Azide, Carbon Monoxide

A
  • Inhibit Complex IV
  • Prevents the Oxidation- reduction because if the iron becomes reduced it eventually has to be reset to be oxidized if it is going to accept more electron to keep the reaction going.
  • Prevent the release of electrons to oxygen
56
Q

Where do CN and N3 bind?

A

Fe3+ of heme a3

57
Q

Where does CO bind?

Affects?

A

Fe2+ of heme a3

2 things: oxygen delivery and mitochondrial respiration and the ability to make ATP —> only survive by glycolysis

58
Q

What is downfall of aerobic respiration?

A

Reactive oxygen species are made

59
Q

3 types of Reactive Oxygen Species

A
  1. O2- superoxide
  2. H2O2 - hydrogen peroxide
  3. OH* - hydroxyl radical
60
Q

O2- superoxide

Properties?
Forms when?
Sources?

A
  • highly reactive
  • limited lipid solubility in PM
  • forms when O2 accepts a single electron
  • Sources: Complex I (quinone structure), Complex II (Flavin group of FAD), CoQ
61
Q

H202 hydrogen peroxide

A

Technically not a radical but can generate an OH radical by accepting an e- and 2 H+

62
Q

OH* hydroxyl radical

Forms when?
Properties?

A
  • Most reactive
  • Formed when H2O2 accepts an e- and 2H+
  • Lipid peroxides
  • Particularly damaging to lipids in PM, esp. unsaturated fatty acids
63
Q

ROS can be generated how?

A

Enzymatically and nonenzymatically

64
Q

Non-enzymatic reactions

A
  1. Haber-Weiss

2. Fenton

65
Q

Haber-Weiss reaction

A

O2- + H2O2 —> OH*

66
Q

Fenton reaction

A

H2O2 in presence of Fe or Cu —> OH* + OH-

67
Q

What are free radicals?

A
  • An independent, free species
  • Have unpaired electrons in orbital —> search for electrons and take from other species.
  • This initiates chain propagating reaction where radical after radical is formed.
  • Most serious when happens in PM
68
Q

What is a radical?

A

NOT free

Doesn’t go anywhere but can be formed and enzyme will continue on with reaction

69
Q

Non enzymatic mechanisms to protect against ROS (2)

A
  1. Vitamin E

2. Vitamin C

70
Q

Vitamin E (alpha-tocopherol)

A
  • Lipid soluble
  • Stored in adipose tissue therefore can be damaging at high concentrations
  • Protects against lipid peroxides / any PM type damage
71
Q

Vitamin C (ascorbic acid)

A
  • Water soluble
  • Excreted in urine
  • Needed for regenerating reduced/protective from of Vitamin E
72
Q

Enzymatic mechanisms for protecting against ROS

A
  1. Superoxide dismutase
  2. Catalase
  3. Glutathione**
73
Q

Catalase

A
  • Converts hydrogen peroxide into water and oxygen

- Found in peroxisomes

74
Q

Superoxide dismutase

A

Converts superoxide into hydrogen peroxide

  • Found in mitochondria, cytosol, extracellular (kidney, liver, heart)
75
Q

Glutathione protective function

A

GSH (reduced form) is more protective

Structure: Glu-Cys-Gly

SH group in Cys acts as nucleophile that can interact with electrophilic compounds. When SH group is oxidized —> form S-S bond with another glutathione molecule

** One of the most important mechanisms against ROS**

76
Q

Enzyme: Glutathione perioxidase

A

2 GSH (reduced) + peroxide —> GSSH (oxidized) + H2O + ROH

77
Q

Enzyme: glutathione reductase (GSH reductase)

A

Takes GSSG and gives GSH

Biochem (15 decks)

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