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
Metabolite Transporters (Carries/Shuttles)
- Glycerol 3-Phosphate - ATP/ADP shuttle - Malate-Aspartate Shuttle - Dicarboxylate Carrier - Tricarboxylate Carrier - Pyruvate carrier - Phosphate carrier
26
Regulation of Electron Transport Chain
ENERGY CHARGE-demand for ATP ``` Respiratory control(acceptor control) -as demand of ATP increases, the rate of ETC increases ```
27
Inhibitors of E.T.C.
- Rotenone - Amytal - Antimycin A - Cyanide - Azide - Carbon Monoxide
28
Rotenone
-inhibits transfer of electrons by Complex I to Coenzyme Q
29
Amytal
-inhibits transfer of electrons by Complex I to Coenzyme Q
30
Antimycin
-Blocks electron flow from cytochrome bH of complex III
31
Cyanide
- Blocks electron flow through complex IV - -reacts with ferric Iron (Fe3+) form of Heme a3 **same as Azide
32
Azide
- Blocks electron flow through complex IV - --reacts with ferric Iron (Fe3+) form of Heme a3 **same as cyanide
33
Carbon Monoxide
- Blocks electron flow through complex IV | - -reacts with Ferrous Iron (Fe2+) form of Heme a3
34
Inhibitors of ATP synthase
1) Oligomycin - antibiotic used to combat fungi (foot fungus) 2) Dicyclohexylcarbodiimide (DCCD) *both prevent movement of H+ through ATP synthase
35
Compounds that Uncouple Electron Transport from ATP synthesis
1) 2,4 Dinitropheno (DNP) | 2) UCP uncoupling protein (UCP-1,2,3)
36
UCP Thermogenin
Some organisms possess the ability to uncouple oxidative phosphorylation from ATP synthesis to generate heat - Hybernating animals - Newborns=Brown fat (adipose tissue)
37
Inhibitors of ATP export
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
Mitochondrial Diseases
Mutation of mitochondria genome Leber hereditary optic neuropathy - Mutant complex I - causes midlife blindness
39
Apoptosis
Programmed Cell Death | -REgulated by mt- Mitochondrial permeability transition pore (mt PTP)
40
Malate-Aspartate Shuttle
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
FADH2 of matrix is worth how much ATP?
2 ATP
42
ATP/ADP Shuttle
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
What is a common structure of mitochondrial transporters?
Tripartite-3 tandem repeats
44
Dismutation
a reaction in which a single reactant is converted into two different products
45
Superoxide Dismutase
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
H2O2 is scavenged by:
Catalase | Glutathione peroxidase
47
What protects against reactive oxygen species? (ROS)
Antioxidant Vitamins (E & C)
48
Reactive Species (ROS)
``` O2=oxygen O2-=Superoxide ion O2^2-=peroxide OH.=hydroxide H2O2=Hydrogen peroxide ```