Biochemistry
6th Edition
ISBN: 9781305577206
Author: Reginald H. Garrett, Charles M. Grisham
Publisher: Cengage Learning
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Textbook Question
Chapter 21, Problem 18P
The Overall Free Energy Change for Photosynthetic NADP+ Reduction
What is the overall free energy change (
4 (700-nm photons) + 4 (680-nm photons) + 2 H2O + 2 NADP+
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The net equation for oxidative phosphorylation can be written as 2NADH + 2 H+ + O2 →2 H2O + 2 NAD+. Write an analogous equation for the light reactions of photosynthesis.
The coenzyme NADP is the terminal electron acceptor in chloroplasts, according to the reaction
2 H₂O + 2 NADP+
2 NADPH + 2 H+ + O₂
Calculate the equilibrium constant, K'eq, for this reaction at 25 °C.
+
Use an E'° of -0.324 V for NADP and 0.816 V for H₂O.
K'eq
=
x10
For the chloroplast, the thylakoid membrane separates the thylakoid lumen from the stroma; the protons from the photosystems are transported, like with the mitochondrial inner membrane, against the gradient from the lumen to the stroma. However, the pH(lumen) – pH (stroma) is much larger, about 3.4. Calculate delta psi (the electric potential) for the thylakoid membrane, given that ∆G of proton transport is about the same as for the mitochondrion. Then comment on its permeability to ions, compared to the mitochondrial inner membrane’s permeability to ions.
Chapter 21 Solutions
Biochemistry
Ch. 21 - P700* Has the Most Negative Standard Reduction...Ch. 21 - Prob. 2PCh. 21 - Prob. 3PCh. 21 - Prob. 4PCh. 21 - The Relative Efficiency of ATP Synthesis in...Ch. 21 - pH and in the Chloroplast Proton-Motive Force...Ch. 21 - Prob. 7PCh. 21 - Prob. 8PCh. 21 - Prob. 9PCh. 21 - Prob. 10P
Ch. 21 - Tracing the Fate of CO2 During Photosynthesis...Ch. 21 - Prob. 12PCh. 21 - Prob. 13PCh. 21 - The Source of the Oxygen Atoms in Photosynthetic...Ch. 21 - Prob. 15PCh. 21 - Prob. 16PCh. 21 - Prob. 17PCh. 21 - The Overall Free Energy Change for Photosynthetic...Ch. 21 - Prob. 19PCh. 21 - Prob. 20PCh. 21 - Prob. 21P
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- The Relative Efficiency of ATP Synthesis in Noncyclic versus Cyclic Photophosphorylation If noncyclic photosynthetic electron transport leads to the translocation of 7 H+/2e- and cyclic photosynthetic electron transport leads to the translocation of 2 H+/e-, what is the relative photosynthetic efficiency of ATP synthesis (expressed as the number of photons absorbed per ATP synthesized) for noncyclic versus cyclic photophosphorylation? (Assume that the CF1CF0-ATP synthase yields 3 ATP/14 H+.)arrow_forwardIn photosynthetic organisms that have two photosystems, a key reason to increase non-cyclic electron flow through photosystem complexes is to:arrow_forwardIn cyclic photophosphorylation, it is estimated that two electrons must bepassed through the cycle to pump enough protons to generate one ATP.Assuming that the ∆G for hydrolysis of ATP under conditions existing inthe chloroplast is about -50 kJ/mol, what is the corresponding percent efficiency of cyclic photophosphorylation, using light of 700 nm?arrow_forward
- Identify the chemical basis for ApH and AY across the chloroplast thylakoid membrane by dragging the descriptions to their targets. Be sure to notice that the upper arrow iindicates ApH and the lower arrow indicates ΔΨ. ATP synthase complex H+ N ADP + P₁ Light energy ATP H*N Photosystem I/II- Chloroplast N side Aus PN ApH T + Thylakoid membrane HTp H+p Lumen Stroma P side Proton circuit A B High H concentration Low positive charge High positive charge Low H+ concentration Within the image, identify the types of proton translocation by dragging each label to its target. O XH₂ 2H+ + Z 2 H* ZH₂ O XH₂ Z 2H+ ZH₂ 2H+ C A B Proton pump Redox looparrow_forwardIn cyclic photophosphorylation, it is estimated that two electrons must be passed through the cycle to pump enough protons to generate one ATP. Assuming that the ΔG for hydrolysis of ATP under conditions existing in the chloroplast is about -50 kJ/mol, what is the corresponding percent efficiency of cyclic photophosphorylation, using light of 700 nm?arrow_forwardIn cyclic photophosphorylation, it is estimated that two electrons must be passed through the cycle to pump enough protons to generate one ATP. Assuming that the AG for hydrolysis of ATP under conditions existing in the chloroplast is about –50 kJ/mol, what is the corresponding percent ef- ficiency of cyclic photophosphorylation, using light of 700 nm?arrow_forward
- In cyclic photophosphorylation, it is estimated that two electrons must be passed through the cycle to pump enough protons to gener- ate one ATP. Assuming that the AG for hydrolysis of ATP under con- ditions existing in the chloroplast is about –50 kJ/mol, what is the corresponding percent efficiency of cyclic photophosphorylation, using light of 700 nm?arrow_forwardConsider 41 NADH and 19 FADH2 molecules funneling electrons into the electron transport chain coupled to oxldative phosphorylation 1. The total number of protons (H") pumped during the oxidation of 41 NADH molecules is 2. The total number of protons (H) pumped during the oxidation of 19 FADH, molecules is 3. The number of ATP molecules produced from the oxidation of 41 NADH molecules is 4. The number of ATP molecules produced from the oxidation of 19 FADH, molecules is 5. The net ATP yield from the oxidation of 41 NADH and 19 FADH, molecules isarrow_forwardWrite the overall net reaction for photosyynthetic Co2 fixation. (Take into account both light and cark reaction of photosynthesis?)arrow_forward
- What is midpoint potential of redox active centers in photosynthetic organisms? What factors affect this? Also how does charge become offset during water oxidation rxns?.arrow_forwardA substantial amount of energy is put into the photosynthetic electron transport to extract electronsf from water and to elevate the energy level of ferredoxin to a very strong reductant. The amount of energy in one NADPH is 218 kJ.mol-1. What is the percentage of this energy conserved in NADPH for the production of one mole of oxygen? What happened to the rest of the energy?arrow_forwardUnder standard conditions, NADH reoxidation by the electron-transport chain has a free-energy change equal to –220 kJ/mol. With 100% efficiency, how many ATP could be synthesized under standard conditions? What is the "actual" efficiency given these numbers?arrow_forward
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