Lecture 6 Electron Transfer Reactions in the Mitochondria Flashcards
What are the electron carriers of the ETC?
- NAD+/NADH
- FAD/FADH2
- FMN/FMNH2
- iron-sulfur clusters
- ubiquinone/ubiquinol
- heme
What is “oxidative phosphorylation“ in mitochondria?
It is the enzymatic phosphorylation of ADP to ATP which is coupled to an electron transfer chain of reactions occurring in the matrix that ultimately reduces O2 to H2O.
Where does oxidative phosphorylation occur?
The ECT occurs on the inner mitochondrial membrane with some reaction happening in the matrix
What does the mitochondrial respiratory chain consist of?
The mitochondrial respiratory chain consists of 4 multisubunit protein complexes (I – IV).
- These multiprotein complexes function as carriers of either 1 or 2 electrons from donors to acceptors.
What is the purpose of the e- moving through the ETC?
When they e- are actively moving through the ETC the energy of the transfer is used to pump protons out of the matrix, through the inner mitochondrial membrane and into the intermembrane space where they accumulate against their electrochemical gradient. there fore the the two side of the membrane become polarized
What is the P and N side of the ETC?
P side = positive side, cytosolic side, relatively high [H+].
N side = negative side, matrix, relatively low [H+].
What are the 2-electron transfer molecules?
- FMN → flavin mononucleotide
- FAD → flavin adenine dinucleotide
- ubiquinone
Structure of FMN
Flavin adenine mononucleotide (FMN) contains an isoalloxazine ring, which undergoes reversible 2- electron reduction to form FMNH2.
- One electron reduction forms a semiquinone
What subunit is FMN on?
Subunit I
Structure of FAD
Analogous to FMN, flavin adenine dinucleotide (FAD) contains an isoalloxazine ring, which undergoes reversible 2-electron reduction to form FADH2.
- Single-electron reduction to form a semiquinone radical is also possible.
What kind of coenzyme is FAD?
prosthetic group → tightly bound to proteins
What subunit is FMN found on?
subunit II
Structure of ubiquinone
Ubiquinone is also called coenzyme Q or simply Q.
Ubiquinone is a mobile, lipid-soluble electron carrier. It has a long, hydrophobic isoprenoid tail. The length of the isoprenoid side chain of ubiquinone is species-specific.
- Ubiquinone that undergoes 1-electron reduction forms semiquinone radical.
- Ubiquinone that undergoes 2-electron reduction becomes ubiquinol (QH2).
How long is the isoprenoid side chain of Q in humans?
Ubiquinone found in humans, ubidecaquinone or coenzyme Q10, has a “tail” of 10 isoprene units (a total of 50 carbon atoms) attached to its benzoquinone “head”.
What structure in ubiquinone similar to?
Similar to benzene
structure of iron-sulphide centers
- The iron is bound to inorganic sulfur atoms or the sulfur atoms of cysteine side chains.
- The iron-sulfur clusters of the respiratory chain are 2Fe-2S, 3Fe-4S or 4Fe-4S clusters
- related to Fe2+ ↔ Fe3+ + 1e
Where are the iron-sulfide clusters found?
complex subunits I and III
Structure of heme
The four N atoms of the porphyrin ring coordinate an iron atom. Because iron can cycle between Fe2+ and Fe3+, heme groups can serve as 1 electron carriers.
- Heme groups absorb visible light and appear as protein pigments.
What types of cytochromes are in the mitochondria?
Mitochondria contain a, b and c-type cytochromes
- Heme a is found in a-type cytochrome.
- Hemes bH and bL is found in complex III, which has the b-type cytochrome.
- Heme c is covalently bound to c-type cytochromes through thioether bonds to two cysteine residues.
- Heme c and Heme a are similar but the latter has a long isoprenoid tail attached to one of the 5-membered rings.
How are the cytochromes of the mitochondria distinguished?
by their absorption spectra
- The absorption spectra of cytochromes change between the oxidized form (Fe3+; red) and the reduced form (Fe2+; blue).
- The exact absorption maximum of the 𝛼 band is sometimes used in the name, such as cytochrome b562.
