Electron Transport Chain Flashcards

1
Q

Where does the Electron Transport chain Occur

A

Inner mitochondrial membrane in the matrix

-contains cristae=folds

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2
Q

Oxidative Phosphorylation

A

Sometimes referred to as Protein Motive Force or Chemiosmotic coupling

1) Protein complexes located in the inter mitochondrial membrane participate in a series of redox reactions (oxidation:reduction)
- use electrons produced from NADH and FADH2 from Krebs cycle

2) energy from electrons used to transport protons across inner mitochondrial membrane
- creates proton gradient (Proton Motive Force); proton gradient and Electrical gradient

3) Proton gradient used to synthesize ATP via ATP synthase

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3
Q

What complexes of the inter mitochondrial membrane pumps protons?

A

Complex I, III, IV

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4
Q

Complex I

  • Structure
  • Function
A

Transmembrane complex-that genes encode on nuclear and mitochondrial genomes

Prosthetic groups:

  • FMN-Flavin mononucleotide
  • Iron Sulfur Centers

Function:

  • oxidized NADH to NAD+ and reduces Q to QH2
  • transports/pumps 4H+/pair of electrons from matrix to inter mitochondrial space
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5
Q

FMN

A

Flavin Mononucleotide (FMN/FMNH2)

  • Prosthetic group
  • Function-electron Carrier-2e-=FMNH2

Comes from vitamin precursor Riboflavin (vitamin B2)

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6
Q

Iron Sulfur Proteins

A

Or Nonheme proteins-ALL PROSTHETIC GROUPS
Function- electron transport-2e- without H+
3 Types:
1)Fe-S contains
-1 Fe, 4 cysteine residues with Sulfur

2) 2Fe-2S contains:
- 2 Fe, 4 cysteine residues with Sulfur, and 2 sulfide ions

3) 4Fe-4S contains
- 4 Fe, 4 cysteine residues with sulfur, and 4 sulfide ions

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7
Q

Irons Oxidated States

A

Fe2+ (ferrous iron)=reduced state

Fe3+ (ferric iron)=oxidized state

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8
Q

Complex II;

  • Structure
  • Function
A

Structure:
-Transmembrane complex of mitochondrial inner membrane associated with succinate dehydrogenase (Enzyme that links Krebs cycle to ETC)

Function:

  • transfers electrons: FADH2->Fe-S-> Q
  • No H+ pumped
  • quinone derived from a long isoprenoid tail
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9
Q

Coenzyme Q

  • Structure
  • Function
A

Structure:
Lipid soluble quinone derived from isoprene units
4 Forms:
-Q=ubiquinone=oxidized form (2C=O)
-QH.-semiquinone=ubiquinone + e- + H+ (OH and O-)
-Q.-semiquinone radical ion=semiquinone loses H+ (2 O-)
-QH2= ubiquinole= ubiquinone + 2e- +2H+ (2 OH’s)

Function:
-accepts 2 e- from complex I via Fe-S or complex II via Fe-S and 2H+ from solution

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10
Q

Complex III

  • Structure
  • Function
A

Structure:
transmembrane complex-cytochrome bc1
1) Prosthetic Groups=iron protoporphyrin IX (alt bw Fe2+/3)
3 Hemes
-Cytochrome B-(2 hemes)
a) BL=low affinity
b) Bh= high affinity
-Cytochrome c1 (one Heme)
1 iron sulfur protein (modified 2Fe-2S)=rieske center
-unusual due to use of His to coordinate Fe instead of Cys
-stabilizes reduced form

Function:

  • Oxidizes QH2 and reduces complex IV
  • transports 4 H+ from matrix to inner membrane space
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11
Q

Cytochrome C

  • structure
  • Function
A

Structure:

  • highly conserved amino acid sequence among many species
  • water soluble protein

Function:
-transports electrons from Complex III to Complex IV

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12
Q

Complex IV

  • structure
  • Function
A

Structure:

  • Transmembrane complex (13 proteins)-> nuclear and mt encode 3 genes
  • Prosthetic Groups
    1) Two Heme A groups: A and A3
    2) 3 copper ions
  • CuA/CuA linked by two cys residues
  • CuB coordinated to 3 His (one His is covalently linked to Tyr)

Function:

  • accepts electrons from cytochrome C
  • transports H+ from matrix to inner membrane space
  • reduces oxygen to water

Protons:

  • 4 protons are pumped
  • 4 protons are used in catalysis (chemical protons)
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13
Q

Coppers oxidized and reduced forms

A

Cu+-Cuprous copper-reduced form

Cu2+-cupric copper-oxidized form

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14
Q

What Is the terminal electron acceptor?

A

O2

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15
Q

Complex IV mechanism

A

All complexes begin reaction in the oxidized state

1) 2 electrons from 2 cytochrome C transferred to complex IV
2) transfer of electrons CuA/CuA-> Heme A-> HemeA3-> Heme CuB
- reduce CuB ad Heme A3 (one electron each)
3) Reduced CuB and Fe in heme A3 bind O2 which extracts electrons forming peroxide bridge
4) Addition of 2 more electrons from 2 cyt C flow to active site along with 2 H+ from CuB^2+-OH and Fe^3+-OH cleaves the peroxide bridge
5) 2H+ react to form H2O which is released

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16
Q

Proton Motive Force

A

Or chemiosmotic coupling
2 Components:
-Proton gradients across mitochondrial inter membrane (pH outside is 1.4 units lower than inside)
-Charge gradient (Charge seperation)

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17
Q

Proton Gradient Provides Energy to multiple biological processes which are:

A
Electron Potential
Heat production 
NADPH synthesis
ATP
Active transport
Flagellar rotation
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18
Q

Complex V

-Structure

A

Or ATP Synthase
Structure
1) F0
-Transmembrane protein contains H+ channel
-Proteins
a) 10-14 c subunits form “c-ring” which forms H+ channel
-tightly linked with gamma and epsilon subunits of F1
-rotation of C ring causes rotation of the Gamma subunit
b)1 a subunit-stationary
c)2 b subunits
d)1 delta subunit

2) F1
- matrix side of mt inner membrane
- Proteins
a) A3B3 hexamer-each beta subunit is chemically different due to interaction with gamma subunit
b) Gamma subunit
c) epsilong subunit

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19
Q

Mechanism of ATP synthesis

A

1) Terminal oxygen of ADP (with associated Mg2+) attacks the phosphorus of Pi forming a pentacovalent intermediate
2) Oxygen of Pi leaves as water upon formation of ATP

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20
Q

Alpha3Beta3 hexamer of ATPsynthase

-Function

A
Beta unit=catalytic subunit 
3 conformations:
L-Loose-ADP and Pi binding
T-tight-ATP synthesis
O-open-ATP released

Gamma subunit rotates counterclockwise sequentially interacting with each beta subunit-altering its conformation

ALpha subunit-not catalytic has ATP bound to it

21
Q

Complex III Mechanism

A

1) QH2 binds
2) 1st e- transfers to rieske center 2Fe-2S-> cytochrome c1->cytochrome C
3) 2nd e- transfers to cytochrome B (both Hemes)->Q.- (radicalized form loss H) to form semiquinone QH.
4) Second QH2 binds
5) 1st e- transfers to rieske center 2Fe-2S-> cytochrome c1->cytochrome C
6) 2 e- + 2H+ (from matrix) transfers to cytochrome B-> Q.- (radical ion) to form reduced form QH2

22
Q

C subunit and A subunit of ATPsynthase

-Structure

A

C subunit:

  • 2 alpha helix structure
  • contains Asp
    a) in high H+ conc of cytoplasm Asp attracts H+ and is protoanted
    b) in low H+ conc of matrix Asp releases H+ into matrix of mitochondria

A subunit:

  • Cytoplasmic Half H+ channel
  • Matrix Half H+ channel
23
Q

Experimental Evidence of Spinning in ATP synthase

A

Cloned A3B3 Hexamer with Gamma subunit attached

  • Actin Filoments attached to Gamma subunit to see direction of rotation
  • amino terminal of Hexamer contains polyhistidine tags that binds nickel tightly on the slide
  • ATP is added and hydrolyzed to ADP + Pi thus gamma subunit spinning in opposite direction of normal conditions
24
Q

Function of Complex V

A

-uses “energy” of proton gradient to phosphorylate ADP to ATP (ATP synthesis inside matrix of mitochondria)

25
Q

Metabolite Transporters (Carries/Shuttles)

A
  • Glycerol 3-Phosphate
  • ATP/ADP shuttle
  • Malate-Aspartate Shuttle
  • Dicarboxylate Carrier
  • Tricarboxylate Carrier
  • Pyruvate carrier
  • Phosphate carrier
26
Q

Regulation of Electron Transport Chain

A

ENERGY CHARGE-demand for ATP

Respiratory control(acceptor control)
-as demand of ATP increases, the rate of ETC increases
27
Q

Inhibitors of E.T.C.

A
  • Rotenone
  • Amytal
  • Antimycin A
  • Cyanide
  • Azide
  • Carbon Monoxide
28
Q

Rotenone

A

-inhibits transfer of electrons by Complex I to Coenzyme Q

29
Q

Amytal

A

-inhibits transfer of electrons by Complex I to Coenzyme Q

30
Q

Antimycin

A

-Blocks electron flow from cytochrome bH of complex III

31
Q

Cyanide

A
  • Blocks electron flow through complex IV
  • -reacts with ferric Iron (Fe3+) form of Heme a3

**same as Azide

32
Q

Azide

A
  • Blocks electron flow through complex IV
  • –reacts with ferric Iron (Fe3+) form of Heme a3

**same as cyanide

33
Q

Carbon Monoxide

A
  • Blocks electron flow through complex IV

- -reacts with Ferrous Iron (Fe2+) form of Heme a3

34
Q

Inhibitors of ATP synthase

A

1) Oligomycin
- antibiotic used to combat fungi (foot fungus)
2) Dicyclohexylcarbodiimide (DCCD)

*both prevent movement of H+ through ATP synthase

35
Q

Compounds that Uncouple Electron Transport from ATP synthesis

A

1) 2,4 Dinitropheno (DNP)

2) UCP uncoupling protein (UCP-1,2,3)

36
Q

UCP Thermogenin

A

Some organisms possess the ability to uncouple oxidative phosphorylation from ATP synthesis to generate heat

  • Hybernating animals
  • Newborns=Brown fat (adipose tissue)
37
Q

Inhibitors of ATP export

A

Atractyloside

  • plant glycoside
  • binds to nucleotide binding site on cytoplasmic side

Bongkreki acid

  • antibiotic from mold
  • binds to nucleotide binding site on matrix side
38
Q

Mitochondrial Diseases

A

Mutation of mitochondria genome

Leber hereditary optic neuropathy

  • Mutant complex I
  • causes midlife blindness
39
Q

Apoptosis

A

Programmed Cell Death

-REgulated by mt- Mitochondrial permeability transition pore (mt PTP)

40
Q

Malate-Aspartate Shuttle

A

In heart and liver, electrons from cytoplasmic NADH are brought into mt by malate-aspartate shuttle

1) electrons are transferred from NADH in the cytoplasm to Oxaloacetate forming malate
2) malate crosses inner mitochondrial membrane and is oxidized to Oxaloacetate
* *Oxaloacetate undergoes transamination to form aspartate -Aspartate can be transported to cytoplasmic side in exchange for Glutamate
3) Glutamate donates amino group to OAA-forming aspartate and alpha ketogluterate
4) In the cytoplasm, aspartate is then deaminated to form oxaloacetate and cycle restarts

41
Q

FADH2 of matrix is worth how much ATP?

A

2 ATP

42
Q

ATP/ADP Shuttle

A

Or ATP/ADP translocate This enzyme changes the equivalents of your body weight in ATP every day

  • Antiport faces cytoplasm and ADP binds causing eversion of antiport into matrix where ADP is released
  • ATP (matrix) binds to ANTIPORT and eversion occurs and ATP is released into cytoplasm (BIND WITHOUT Mg2+)

Mt matrix is more negative than cytoplasm due to transport of H+ out of mt and OH- remains
VOLTAGE POTENTIAL POWERS THE TRANSFER of ADP/ATP

43
Q

What is a common structure of mitochondrial transporters?

A

Tripartite-3 tandem repeats

44
Q

Dismutation

A

a reaction in which a single reactant is converted into two different products

45
Q

Superoxide Dismutase

A

Scavenges reactive oxygen species

  • Two forms of Superoxide Dismutase in eukaryotes:
    1) Mn2+ in mt
    2) Cu2+ and Zn+ in cytoplasm

Oxidized form accepts electtrons from O2-

  • enzyme is reduced
  • O2- is oxidized to O2

Reduced form uses e- + 2H+ to reduce another O2

46
Q

H2O2 is scavenged by:

A

Catalase

Glutathione peroxidase

47
Q

What protects against reactive oxygen species? (ROS)

A

Antioxidant Vitamins (E & C)

48
Q

Reactive Species (ROS)

A
O2=oxygen
O2-=Superoxide ion
O2^2-=peroxide
OH.=hydroxide 
H2O2=Hydrogen peroxide