Electron Transport Chain Flashcards
Where does the Electron Transport chain Occur
Inner mitochondrial membrane in the matrix
-contains cristae=folds
Oxidative Phosphorylation
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
What complexes of the inter mitochondrial membrane pumps protons?
Complex I, III, IV
Complex I
- Structure
- Function
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
FMN
Flavin Mononucleotide (FMN/FMNH2)
- Prosthetic group
- Function-electron Carrier-2e-=FMNH2
Comes from vitamin precursor Riboflavin (vitamin B2)
Iron Sulfur Proteins
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
Irons Oxidated States
Fe2+ (ferrous iron)=reduced state
Fe3+ (ferric iron)=oxidized state
Complex II;
- Structure
- Function
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
Coenzyme Q
- Structure
- Function
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
Complex III
- Structure
- Function
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
Cytochrome C
- structure
- Function
Structure:
- highly conserved amino acid sequence among many species
- water soluble protein
Function:
-transports electrons from Complex III to Complex IV
Complex IV
- structure
- Function
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)
Coppers oxidized and reduced forms
Cu+-Cuprous copper-reduced form
Cu2+-cupric copper-oxidized form
What Is the terminal electron acceptor?
O2
Complex IV mechanism
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
Proton Motive Force
Or chemiosmotic coupling
2 Components:
-Proton gradients across mitochondrial inter membrane (pH outside is 1.4 units lower than inside)
-Charge gradient (Charge seperation)
Proton Gradient Provides Energy to multiple biological processes which are:
Electron Potential Heat production NADPH synthesis ATP Active transport Flagellar rotation
Complex V
-Structure
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
Mechanism of ATP synthesis
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
Alpha3Beta3 hexamer of ATPsynthase
-Function
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
Complex III Mechanism
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
C subunit and A subunit of ATPsynthase
-Structure
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
Experimental Evidence of Spinning in ATP synthase
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
Function of Complex V
-uses “energy” of proton gradient to phosphorylate ADP to ATP (ATP synthesis inside matrix of mitochondria)
Metabolite Transporters (Carries/Shuttles)
- Glycerol 3-Phosphate
- ATP/ADP shuttle
- Malate-Aspartate Shuttle
- Dicarboxylate Carrier
- Tricarboxylate Carrier
- Pyruvate carrier
- Phosphate carrier
Regulation of Electron Transport Chain
ENERGY CHARGE-demand for ATP
Respiratory control(acceptor control) -as demand of ATP increases, the rate of ETC increases
Inhibitors of E.T.C.
- Rotenone
- Amytal
- Antimycin A
- Cyanide
- Azide
- Carbon Monoxide
Rotenone
-inhibits transfer of electrons by Complex I to Coenzyme Q
Amytal
-inhibits transfer of electrons by Complex I to Coenzyme Q
Antimycin
-Blocks electron flow from cytochrome bH of complex III
Cyanide
- Blocks electron flow through complex IV
- -reacts with ferric Iron (Fe3+) form of Heme a3
**same as Azide
Azide
- Blocks electron flow through complex IV
- –reacts with ferric Iron (Fe3+) form of Heme a3
**same as cyanide
Carbon Monoxide
- Blocks electron flow through complex IV
- -reacts with Ferrous Iron (Fe2+) form of Heme a3
Inhibitors of ATP synthase
1) Oligomycin
- antibiotic used to combat fungi (foot fungus)
2) Dicyclohexylcarbodiimide (DCCD)
*both prevent movement of H+ through ATP synthase
Compounds that Uncouple Electron Transport from ATP synthesis
1) 2,4 Dinitropheno (DNP)
2) UCP uncoupling protein (UCP-1,2,3)
UCP Thermogenin
Some organisms possess the ability to uncouple oxidative phosphorylation from ATP synthesis to generate heat
- Hybernating animals
- Newborns=Brown fat (adipose tissue)
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
Mitochondrial Diseases
Mutation of mitochondria genome
Leber hereditary optic neuropathy
- Mutant complex I
- causes midlife blindness
Apoptosis
Programmed Cell Death
-REgulated by mt- Mitochondrial permeability transition pore (mt PTP)
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
FADH2 of matrix is worth how much ATP?
2 ATP
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
What is a common structure of mitochondrial transporters?
Tripartite-3 tandem repeats
Dismutation
a reaction in which a single reactant is converted into two different products
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
H2O2 is scavenged by:
Catalase
Glutathione peroxidase
What protects against reactive oxygen species? (ROS)
Antioxidant Vitamins (E & C)
Reactive Species (ROS)
O2=oxygen O2-=Superoxide ion O2^2-=peroxide OH.=hydroxide H2O2=Hydrogen peroxide
