Electron Transport Chain Flashcards
What is the structure of the Mitochondria?
- Intracellular organelle as big as a bacterium
- It has two membranes, an inner and outer mitochondrial membrane.
- It has its own DNA encoding some of the genes required for ETC and other functions
- Has own transcription and translation machinery, the mitochondrial ribosomes. These are similar to those of bacteria.
Is the oxidation of NADH and FADH2 exergonic or endergonic?
The oxidation of these two molecules is extremely exergonic.
What are three ways in which electrons can be transferred?
- Direct electron transfer (eg. Fe3+ to Fe2+)
- Transfer of H atom
- Transfer of Hydride ion, as in NADH oxidation to NAD+
What are some membrane-bound electron carriers?
- Ubiquinone or Coenzyme Q
- Flavoproteins
- Iron-Sulfur proteins
- Cytochromes
What are some qualities of Ubiquinone (Coenzyme Q)?
- It is a highly hydrophobic, lipid-soluble benzoquinone with a long isoprenoid side chain.
- Can accept one electron to become semiubiquinone radical or two electrons to become ubiquinol.
- can freely diffuse through lipid bilayer, shuttling electrons among less mobile carriers
- Can carry both electrons and protons, playing a central role in coupling electron flow to proton movement.
What are some qualities of flavoproteins?
- Proteins tightly bound to flavin nucleotides (FMN or FAD)
- Capable of accepting/donating one or two electrons
- reduction potential of flavin nucleotides depends on the protein it is bound to.
What are some qualities of Iron-Sulfur Proteins?
- Fe atoms coordinated to Sulfur atoms of either Cys residues of the proteins or also with inorganic sulfur atoms. The Fe is either oxidized or reduced
- Reduction potential varies depending on microenvironment around Fe atom in the protein.
What are some qualities of Cytochromes?
- Proteins with an Fe-containing heme prosthetic group
- absorbs light in the visible range due to heme group
- three classes of cytochromes depending on the heme group they have
What are the differences between the three cytochromes?
- Cytochrome a and b are non-covalently bound to protein, c is covalently bound
- Cytochrome a and b are membrane proteins whereas cytochrome c in the mitochondria is a soluble protein associated with the outer surface of the membrane by electrostatic interaction
What is complex 1 of the ETC?
NADH-Coenzyme Q Oxidoreductase:
largest protein complex in mitochondria (43 polypeptides, 850kDa heavy)
contains 6-7 iron-sulfur clusters and 1 FMN as prosthetic group
Has a binding site for Coenzyme Q, which is a substrate for this complex
What is complex 2 of the ETC?
Succinate Dehydrogenase:
Contains 4 different proteins
What is Comlex 3 of the ETC?
Cytochrome bc1 Complex or
Ubiquinone: Cytochrome c Oxidoreductase complex.
- Is a dimer of two identical complexes, each containing 11 different subunits.
- The Q cycle occurs within complex 3
What is the Q cycle?
Electrons from two electron carriers are transferred throughout complex 3.
- The first electron follows the path
QH2 –>Fe-S->Cyt c1 –>Cyt c
- The second electron follows the path
QH2–>Cyt bL–>cyt bH–>oxidized Q, creating an unstable Q-.
- The Q- ion is converted back into Q by taking 2H+ from the matrix side. The QH2 is then recycled back into the Q cycle.
What is complex 4 of the ETC?
Cytochrome c Oxidase:
- Catalyses the transfer of electrons from cyt c to Oxygen, leading to the reduction of Oxygen into H2O
- The complex has 13 subunits and a weight of 240 kDa
What are the three proteins critical for electron flow in Complex 4 of the ETC?
Subunits 1,2, and 3:
Subunit 1 contains two heme groups and a Cu ion
Subunit 2 contains two Cu atoms bonded by two sulfur atoms of Cystine
Subunit 3 role is not well understood but critical for complex 4 function
