Key to Oxidative Phosphorylation Exercise |
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ATP Synthase
1. a. F1; b. Fo; c. Both F1 (the β subunits) and Fo (the position of the c ring) change conformation; d. clockwise; e. counterclockwise.
2. The active site changes from the loose conformation to the tight conformation and forms a covalent bond between ADP and Pi, making ATP, as a result of the movement of protons from P to N through Fo. When more protons move through Fo, the tight conformation changes to the open conformation, and ATP is released.
3. H+ enters a half channel in the a subunit that is open to the P side.
An Asp− side chain on a c chain (part of the c ring) accepts the H+, becoming Asp-COOH.
This can move into the bilayer (clockwise), which allows another c-Asp− to move into position to accept another H+.
When this has happened several times, the original H+ is exposed to the half channel in the a subunit that is open to the N side of the membrane.
Asp-COOH then donates H+, which diffuses into the matrix.
4. a. 10 H+'s; b. 6 H+'s; c. 2.5 ATP's for each NADH; 1.5 ATP's for each FADH2.
5. The uncoupler allows H+ to cross the membrane P to N without going through ATP synthase. The number of ATP's per NADH or FADH2 is reduced.
6. When histidine accepts H+, it has a positive charge on its side chain. When aspartate accepts H+, it has no net charge on its side chain. Moving a charged side chain so that it is exposed to lipid is unfavorable.
7.
Table 1: ATP's Produced by Degrading One Glucose |
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pathway |
number produced per glucose |
total H+ moved from N to P |
number of ATP's |
glycolysis ATP's (net) |
2 |
0 |
2 |
glycolysis NADH's |
2 |
20 |
5 |
PDH NADH's |
2 |
20 |
5 |
citric acid cycle NADH's |
6 |
60 |
15 |
citric acid cycle FADH2's |
2 |
12 |
3 |
citric acid cycle GTP's |
2 |
0 |
2 |
Total |
32 |
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Shuttles
1. Malate, α-ketoglutarate, aspartate, and glutamate are all much smaller than NADH and are therefore more easily moved across the membrane by a transporter.
Malate and α-ketoglutarate both have a net charge of −2 at pH 7.
Aspartate and glutamate both have a net charge of −1 at pH 7.
2. a. Cytosolic malate dehydrogenase using NADH produced in glycolysis.
b. By the malate/ α-ketoglutarate transporter.
c. Malate ↔ oxaloacetate by matrix malate dehydrogenase, using NAD+ from oxidation of NADH by complex I of electron transport.
d. Oxaloacetate is converted to aspartate by transferring an amine group to it and then moved by the aspartate/glutamate transporter.
3. The process of moving NADH into the mitochondrial matrix by the malate/aspartate shuttle is one of diffusion rather than active transport because the molecules move down their concentration gradients and the transporters do not require ATP in order to move them from one side of the membrane to the other.
4.
Table 2: Two NADH Shuttles |
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Characteristic |
Malate-Aspartate Shuttle |
Glycerol-3-Phosphate Dehydrogenase |
Enzyme that oxidizes NADH |
malate dehydrogenase |
glycerol-3-P dehydrogenase |
Cytosol enzyme substrate (oxidized molecule) |
oxaloacetate |
dihydroxyacetone-P |
Cytosol enzyme product (reduced molecule) |
malate |
glycerol-3-P |
Mitochondrial enzyme product |
oxaloacetate |
dihydroxyacetone-P |
Reduced coenzyme in the mitochondrion |
NADH |
FADH2 (QH2) |
# ATP produced after oxidizing 2 cytosol NADH |
5 |
3 |
5. a. The charge component of ΔGT= + 19.3 kJ/mol for moving H2PO4− into the matrix.
b. The charge component of ΔGT = − 19.3 kJ/mol for moving H+ into the matrix.
c. Since [H+] and probably also [H2PO4−] is lower on the N side, the concentration component for transporting solutes across a membrane is negative. With the charge components equal (one > 0 and one < 0), the overall ΔGT is < 0.
6. Electron transport