How Does the Reducing Equivalents Go from the Cytoplasm to the Mitochondrion?
Autor: may3000 • March 15, 2017 • Study Guide • 572 Words (3 Pages) • 849 Views
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- How does the reducing equivalents go from the cytoplasm to the mitochondrion? They don’t cross the membrane, but electrons do through two ways:
- Glycerol 3-phosphate shuttle:
- In cytoplasm, DHAP is reduced to glycerol 3-phospahe by NADH. Enzyme: cytoplasmic Glycerol 3-phoshate dehydrogenase.
- FAD is reduced to FADH2 in the enzyme called mitochondrion Glycerol 3-phoshate dehydrogenase. FAD is prosthetic group in the enzyme.
- Ubiquinone (Q) is reduced to Ubiquinol (QH2)
- Malate-Aspartate shuttle:
- In cytoplasm, OAA + NADH → Malate + NAD+. Enzyme: cytoplasmic Malate dehydrogenase.
- Malate is transported into the Matrix
- Malate + NAD+ → OAA + NADH. Enzyme: Mitochondrial Malate dehydrogenase.
- Glutamate is transformed to a-Ketoglutarate , and OAA is transformed to Aspartate. Enzyme: Mitochondrion Aspartate amino transferase.
Glu+ OAA → Asp + a-ketoglutarate.
- Asp + a-ketoglutarate are transported to the cytoplasm.
- Asp + a-ketoglutarate → Glu+ OAA. Enzyme: cytoplasmic Aspartate amino transferase.
- The more negative Eo, the greater the electron-transfer potential and the greater the tendency to donate electrons. The more positive Eo, the greater the greater the tendency to accept electrons.
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- Electron Transport Chain: Integral proteins
- Complex I (NADH-Q oxidoreductase, NADH dehydrogenase):
- Pumps protons? Yes
- Electron source: NADH
- Electron carriers: FMN – multiple Fe-S centers
- Ultimately reduce: Ubiquinone
- Complex II (Succinate-Q reductase, succinate dehydrogenase):
- Pumps protons? No
- Electron source: Succinate
- Electron carriers: FAD – multiple Fe-S centers
- Ultimately reduce: Ubiquinone
- Complex III (Q-cytochrome C oxidoreductase):
- Pumps protons? Yes
- Electron source: Ubiquinol
- Electron carriers: 3 cytochromes– Rieske Fe-S centers
- Ultimately reduce: Cytochrome C
- Complex IV (Cytochrome C oxidase):
- Pumps protons? Yes
- Electron source: cytochrome C
- Electron carriers: CuA/cytochrome a- CuB/cytochrome a3
- Ultimately reduce: O2
- Ubiquinone (oxidized) / Ubiquinol (reduced)
- Hydrophobic; travels within the inner membrane
- Accepts electrons from G3P, complex I, and complex II.
- Carries electrons to complex III.
- There is semiquinone intermediate.
- Cytochrome C
- Hydrophilic; travels within the intermembrane space.
- Accepts electrons complex III
- Carries electrons to complex IV.
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- Complex III has 3 cytochromes that contain hemes: bH, bL, c1. Electrons are transported from one Fe to another until reaching rieske Fe-S center. They are coordinated by cysteines and histidines.
- In complex IV:
- 2 cytochromes C transfers electrons to reduce CuB/heme a3
- reduced CuB/heme a3 bind oxygen to form peroxide bridge.
- 2 electrons and 2 protons cleaves the bridge.
- 2 more protons release the water
- there are histidine and tyrosine adducts
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- Mitochondrial ATP synthasome:
- ATP synthase
- ATP/ADP antiporter
- Inorganic phosphate transporter
- ATP synthase has two regions:
- F0: region in which protons flow.
- F1: the site of ATP synthesis using rotational energy.
- Rotating components:
- C rings: contains Apartate/ Aspartic acid
- γ: central shaft; asymmetric; cause change in β subunits when rotating
- ε
- Stationary components:
- Stator:
- a: cytoplasmic half channel/matrix half channel
- b2
- δ
- Hexameric ring:
- α3: for structure
- β3: site of ATP synthesis
- Conformations in β subunits:
- Open: ADP and P are bound; ATP is released
- Loose: ADP and P are bound
- Tense: ATP is synthesized.
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