Photorespiration is a multienzyme bypass of the Calvin cycle's CO2 fixation process in plants and all other oxygenic phototrophs. This bypass removes and recycles 2-phosphoglycolate, a damaging by- product of photosynthesis in the presence of 02, which is formed when 02 substitutes CO2 in the CO2 fixation pathway. Discuss the situation of fixing 02 (oxygen) rather than CO2 (carbon dioxide) in plants.

Photorespiration is a multienzyme bypass of the Calvin cycle's CO2 fixation process in plants and all other oxygenic phototrophs. This bypass removes and recycles 2-phosphoglycolate, a damaging by- product of photosynthesis in the presence of 02, which is formed when 02 substitutes CO2 in the CO2 fixation pathway. Discuss the situation of fixing 02 (oxygen) rather than CO2 (carbon dioxide) in plants.

Biochemistry

6th Edition

ISBN:9781305577206

Author:Reginald H. Garrett, Charles M. Grisham

Publisher:Reginald H. Garrett, Charles M. Grisham

Chapter21: Photosynthesis

Section: Chapter Questions

Problem 5P: The Relative Efficiency of ATP Synthesis in Noncyclic versus Cyclic Photophosphorylation If...

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Photorespiration is a multienzyme bypass of the Calvin cycle's CO2 fixation process in plants and all other oxygenic phototrophs. This bypass removes and recycles 2-phosphoglycolate, a damaging by- product of photosynthesis in the presence of O2, which is formed when 02 substitutes CO2 in the CO2 fixation pathway. According to a regional scale model, photorespiration currently reduces US soybean and wheat yields by 36% and 20%, respectively, and a 5% reduction in photorespiration losses would be worth around $500 million yearly in the United States. Can you forecast the costs and good advantages of C4 photosynthesis? What factors increase the likelihood that the benefits will outweigh the expenses in hot, dry areas in the United States?
Which of the following scenarios does not occur during the reduction phase of the Calvin Cycle? Hide answer choices Each molecule of 3-phosphoglycerate is phosphorylated by ATP to form 1,3-bisphosphoglycerate. Each molecule of 1,3-bisphosphoglycerate is reduced to glyceraldehyde 3-phosphate by the addition of two electrons from NADPH. Glyceraldehyde 3-phosphate is converted into Ribulose bisphosphate. Some of the glyceraldehyde 3-phosphate molecules are used in carbohydrate production.
A culture of the single celled organism Chlamydomonas is actively carrying out photosynthesis in the presence of light and CO2. If you turned off the light, how would you expect the amounts of ribulose 1,5-bisphosphate and 3-phosphoglycerate to change over the next minute? How about if you left the light on and removed the CO2? Please answer these questions with specific references to the Calvin cycle.
It is believed that the ratio of cyclic photophosphorylation to noncyclicphotophosphorylation changes in response to metabolic demands. Ineach of the following situations, would you expect the ratio to increase,decrease, or remain unchanged?(a) Chloroplasts carrying out both the Calvin cycle and the reduction ofnitrite (NO2-) to ammonia (This process does not require ATP.)(b) Chloroplasts carrying out not only the Calvin cycle but also extensiveactive transport(c) Chloroplasts using both the Calvin cycle and the C4 pathway
In photosynthetic organisms that have two photosystems, a key reason to increase non-cyclic electron flow through photosystem complexes is to:
It is believed that the ratio of cyclic photophosphorylation to noncyclic photophosphorylation changes in response to metabolic demands. In each of the following situations, would you expect the ratio to increase, decrease, or remain unchanged? (a) Chloroplasts carrying out both the Calvin cycle and the reduction of nitrite (NO2 -) to ammonia (This process does not require ATP.) (b) Chloroplasts carrying out not only the Calvin cycle but also extensive active transport (c) Chloroplasts using both the Calvin cycle and the C4 pathway
What is the chemical formula for photosynthesis? Discuss why (1) Sunlight and water are required for photosynthesis, and (2) Which molecule is reduced, and which is oxidized. Describe in detail the structure and function of the electron transport chain. Discuss how the light-dependent reactions and the Calvin cycle act synergistically to produce food for plants.
In the Light Reaction of Photosynthesis, the sun excites electrons in pigment molecules in the photosystems. These excited electrons and (H+ ions) go through electron transport systems. Keep in mind that if this process continued as stated, the pigment molecules would run out of electrons, but fortunately there is a way in which the excited electrons are replaced. Explain how the electrons are ultimately replaced and what the important byproduct is.
A decrease in entropy occurs during the CO2 uptake phase of the Calvin cycle, as freely moving CO2 molecules become fixed into a carbon skeleton. How can this occur without direct participation by NADPH and/or ATP?
a) Draw the carboxylation reaction mechanism catalyzed by Rubisco. Include the substrates, products, key amino acid residues in the active site, and important metal ions. b) Describe each step in the Rubisco carboxylation reaction and why the carbamylated lysine is critical for enzyme activity. c. Describe the purpose of the "regeneration stage" of the Calvin-Benson cycle.
In cyclic photophosphorylation in photosystem I, ATP is produced, even though water is not split. Explain how the process takes place.
Explain how the mechanism of ATP generation in the chloroplast similar to that in the mitochondria? What molecule serves as the terminal e- acceptor in the electron transport system of aerobic respiration? (Or how is this acceptor different from the terminal e- acceptor of the electron transport system in the chloroplast?) Why does respiration rarely meet its theoretical maximum energy yield? (Hint: In class we identified three potential reasons. Sketch the "dumbbell" model of a plant with equal size leaf and root compartments. On the model identify the major environmental controllers of respiration rate in the leaf and What are the major environmental controls over respiration rate in the above and below ground compartment of a plant? On a graph of respiration rate (Y-axis) and time of day, 0 through 24 h (X-axis) sketch the diurnal time course of leaf respiration and root respiration.