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What significant stepin sugar synthesis happens in each phase? 6.

You don't need to know the compounds named, just a summary of what happens in that phase as listed:

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Theydiffer in specific form in which carbon dioxide is transported.

As we have seen, photosynthetic cells produce O2 (by the splitting of H2O)and use CO2 to produce 3-phosphoglycerate with a net gaseous changeduring photosynthesis that can be written as follow:

CO2 + H2O → O2 + (CH2O)

In the dark plants are carrying out mitochondrial respiration bythe oxidation of substrates to CO2 and theconversion of O2 to H2O. On top of that, there is another processin plants that, like mitochondrial respiration, consumesO2 and produces CO2 and, like photosynthesis, is drivenby light. This process is called photorespiration and is a costlyside reaction of photosynthesis. In this section we describethis process and the strategies plants use tominimize its metabolic consequences.

In other words, the first product of carbon dioxidefixation is a 3-carbon compound (PGA).

In a broad chemical sense, the opposite of photosynthesis isrespiration. Most of life on this planet (all except in the deepsea vents) depends on the reciprocal photosynthesis-drivenproduction of carbon containing compounds by a series of reducing(adding electrons) chemical reactions carried out by plants andthen the opposite process of oxidative (removing electrons)chemical reactions by animals (and plants, which are capable ofboth photosynthesis and respiration) in which these carboncompounds are broken down to carbon dioxide and water.

PEPcase This is the initial enzyme that fixes carbon dioxide.

In your own words, describe the end result of the light reactions. 4.

Step in which the temporary chemical (ATP) and reducing (NADPH)potentials that were generated in the light-dependent reactions are used to reduce the PGA(an acid) to a carbonyl (glyceraldehyde 3-phosphate; abbreviated G3P or GAP)

Regulation of the Calvin Cycle
We will not cover this in class except to say thatregulation of the cycle is obviously important. There are several regulatory controls:

how are carbohydrate made in photosynthesis? | …

In your own words, describe the three phases  of the Calvin Cycle Reactions.

Starch synthase in chloroplasts and amyloplastscatalyzes the addition of single glucoseresidues, donated by ADP-glucose, to thereducing end of a starch molecule by atwo-step insertion mechanism. Branches inamylopectin are introduced by a secondenzyme. Sucrose is synthesized in the cytosol in twosteps from UDP-glucose and fructose1-phosphate. The partitioning of triose phosphates betweensucrose synthesis and starch synthesis isregulated by fructose 2,6-bisphosphate(F2,6BP), an allosteric effector of the enzymesthat determine the level of fructose6-phosphate. F2,6BP concentration variesinversely with the rate of photosynthesis, andF2,6BP inhibits the synthesis of fructose6-phosphate, the precursor to sucrose.

Triose phosphates produced by the Calvin cycle inbright sunlight, as we have noted, may be stored temporarilyin the chloroplast as starch, or converted to sucroseand exported to nonphotosynthetic parts of theplant, or both. The balance between the two processesis tightly regulated, and both must be coordinated withthe rate of carbon fixation. Five-sixths of the triosephosphate formed in the Calvin cycle must be recycledto ribulose 1,5-bisphosphate; if more thanone-sixth of the triose phosphate is drawn out of thecycle to make sucrose and starch, the cycle will slow orstop. However, insufficient conversion of triose phosphateto starch or sucrose would tie up phosphate, leavinga chloroplast deficient in Pi, which is also essentialfor operation of the Calvin cycle.
The flow of triose phosphates into sucrose is regulatedby the activity of fructose 1,6-bisphosphatase(FBPase-1) and the enzyme that effectively reverses itsaction, PPi-dependent phosphofructokinase.These enzymes are therefore critical points fordetermining the fate of triose phosphates produced byphotosynthesis. Both enzymes are regulated by fructose2,6-bisphosphate (F2,6BP), which inhibits FBPase-1and stimulates PP-PFK-1. In vascular plants, the concentrationof F2,6BP varies inversely with the rate ofphotosynthesis (Fig. 20–26). Phosphofructokinase-2,responsible for F2,6BP synthesis, is inhibited by dihydroxyacetonephosphate or 3-phosphoglycerate andstimulated by fructose 6-phosphate and Pi. During activephotosynthesis, dihydroxyacetone phosphate isproduced and Pi is consumed, resulting in inhibition ofPFK-2 and lowered concentrations of F2,6BP. This favorsgreater flux of triose phosphate into fructose 6-phosphate formation and sucrose synthesis. With thisregulatory system, sucrose synthesis occurs when thelevel of triose phosphate produced by the Calvin cycleexceeds that needed to maintain the operation of thecycle.
The key regulatory enzyme in starch synthesis isADP-glucose pyrophosphorylase (Fig. 18–14); it isactivated by 3-phosphoglycerate (which accumulatesduring active photosynthesis) and inhibited by Pi (whichaccumulates when light-driven condensation of ADPand Pi slows). When sucrose synthesis slows, 3-phosphoglycerateformed by CO2 fixation accumulates, activatingthis enzyme and stimulating the synthesis ofstarch.

Photorespiration Light stimulated production of carbon dioxide in the presence of oxygen
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  • one molecule is the initial end product of photosynthesis; ..

    In other words, it takes a greater amount of carbon dioxide to break even.

  • in photosynthesis, carbohydrate ..

    fluence for tobacco and maize at ambient oxygen at varying carbon dioxide levels.

  • Autotrophism: Carbon Reactions (Calvin Cycle, C4, CAM)

    In addition to its normal substrate (carbon dioxide) rubisco alsobinds oxygen to RuBP.

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NOVA - Official Website | Illuminating Photosynthesis

When the chlorophyll molecule is excited by light, the energylevel of an electron in its structure is "boosted to ahigher energy level and this "excited" chlorophyll (nowis called an ) moves rapidly the the reactioncenter of the Photosystem I where it transfers its extra energyto an electron which is then expelled from the reaction centerand is accepted by the first member of a chain of electroncarriers and ultimately reaches NADP+, reducing it to NADPH. Thereaction center has lost an electron and this "electronhole" is filled by by stripping electrons from water whichleaves hydrogen ion (H+) and molecular oxygen (O2). The pathwayof electrons from water to NADP+ has "Z" shape whendiagramed and is refered to as the Z Scheme.

01/01/2011 · Illuminating Photosynthesis

fluence for tobacco and maize in ambient oxygen (21%); (b) light saturation point - point at which increasing fluence yields a constant amount of photosynthesis; (c) light compensation point - fluence at which the amount of photosynthesis just equals the amount of respiration; and (d) note that plants that photorespire (like tobacco) have a higher light compensation point and light saturate.

Concept 1: An Overview of Photosynthesis - …

The Z Scheme diagram shows the pathway of an electron fromwater (lower right) to NADP+ (upper left). It also shows theenergy relationships which are measured as voltage potentialshown on the scaleon the right. To raise the energy of theelectrons derived from water (+0.82 volts) to the level necessaryto reduce NADP+ to NADPH (-0.32 volts), each electron must beboosted twice (vertical red arrows) by light energy absorbed inPhotosystems I and II. After each boosting , the energizedelectrons flow "downhill" (diagonal black lines) and inthe process transfer some of their energy to a series ofreactions which ultimately adds a phosporus to ADP to producehigh energy ATP and reduces NADP+ to NADPH. There is analternative shunt whereby the electron flow turns back tocytochrome b563 (green line)and this is called and it occurs when there is no need for NADPH, so onlyATP is produced.

Chemistry for Biologists: Photosynthesis

Chloroplasts have many shapes in different species but aregenerally fusiform shaped (and much larger than mitochondria) andhave many flattened membrane-surrounded vesicles called thylakoidswhich are arranged in stacks called grana. Thesethylakoid membranes contain all of the photosynthetic pigments ofthe chloroplast and all of the enzymes required for Light Phasereactions. The fluid in the stroma surrounding the thylakoidvesicles contains most of the enzymes for Dark phase reactions.

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