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.
Plant photosynthesis, both the Light Phase and Dark phasereactions, takes place in chloroplasts, which may be regarded asthe "power plants" of the green leaf cells. At night,when there is no sunlight energy, ATP continues to be generatedfor the plant's needs by respiration, i.e., oxidation of(photosynthetically produced) carbohydrate in mitochondria(similar to animals).
The oxidative chemical reactions of respiration releaseenergy, some of which is heat and some of it is captured in theform of high energy compunds such as Adenosine triphosphate (ATP)and Nicotinamide adenide dinucleotide phosphate (NADPH). Thesecompounds have a high energy (unstable) terminal phosphate bondand that terminal phosphate is easily detached with the transferof the energy to drive chemical reactions in the synthesis ofother biomolecules. In this case, the ATP loses one phosphate tobecome the energy-depleted ADP (Adenosine diphosphate)and the NADPH loses one electron to become energy-depleted NADP+.
Photosynthesis converts these energy- depleted compounds (ADPand NADP+) back to the high energy forms (ATP and NADPH) and theenergy thus produced in this chemical form is utilized to drivethe chemical reactions necessary for synthesis of sugars andother carbon containing compounds (e.g., proteins, fats). Theproduction of high energy ATP and NADPH in plants occurs in whatis known as Light Phase Reactions (Z Scheme) (requiressunlight). The energy releasing reactions which converts themback to energy-depleted ADP and NADP is known as Dark PhaseReactions (Calvin Cycle) (does not require light) in whichthe synthesis of glucose and other carbohydrates occurs.
So we can summarize by saying that the photosynthetic plantstrap solar energy to form ATP and NADPH (Light Phase) and thenuse these as the energy source to make carbohydrates and otherbiomolecules from carbon dioxide and water (Dark Phase),simultaneously releasing oxygen in to the atmosphere. Thechemoheterotrophic animals reverse this process by using theoxygen to degrade the energy-rich organic products ofphotosynthesis to CO2 and water in order to generate ATP fortheir own synthesis of biomolecules.
But in terms of function and structure, the photosystem reaction centers fall into two categories that differ in almost every way. Photosystem I serves mainly to produce the energy carrier NADPH, whereas photosystem II makes ATP and splits water molecules. Their reaction centers use different light-absorbing pigments and soak up different portions of the spectrum. Electrons flow through their reaction centers differently. And the protein sequences for the reaction centers don’t seem to bear any relation to each other.
of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign Introduction.
Photosynthesis, play_circle_outline plants: photosynthesis Encyclopædia Britannica, Inc.
Both types of photosystem come together in green plants, algae and cyanobacteria to perform a particularly complex form of photosynthesis—oxygenic photosynthesis—that produces energy (in the form of ATP and carbohydrates) as well as oxygen, a byproduct toxic to many cells. The remaining photosynthetic organisms, all of which are bacteria, use only one type of reaction center or the other.
At first, most scientists did not believe that all the reaction centers found in photosynthetic organisms today could possibly have a single common ancestor. True, all reaction centers harvest energy from light and lock it into compounds in a form that’s chemically useful to cells. To do this, the proteins pass electrons along a transfer chain of molecules in a membrane, as though skipping along a series of stepping stones. Each step releases energy that’s ultimately used down the line to make energy-carrier molecules for the cell.
the process by which green plants and certain other organisms transform.
Photosynthesis Problem Set 1 Problem 2 Tutorial: Energy source for ATP formation The specific energy source for the reaction ADP + phosphate ATP by the enzyme.
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Now what are the "Dark Phase Reactions" (aka CalvinCycle)? This is the cycle that converts CO2 into glucose. Sinceit utilizes the chemical energy in the ATP and NADPH, it does notrequire sunlight (hence the name). It is a complex cycle ofmostly phosphorylation (adding or removing phosphate) andoxidative (electron removal) chemical reactions whereby 6molecules of CO2 are converted into one molecule of glucose. Itrequires the energy-releasing cleavage of high energy bonds of 18ATPs and 12 NADPHs . The resulting 18 ADPs and 12 NADP+s are thenrestored by the Light Phase process to their high energy forms(ATP and NADPH).
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Photosynthesis is a process in which light energy is used to produce sugar and other organic compounds.
For each electron flowing from water to NADP+ (a net change in1.14 volts), two quanta of light are absorbed, one by eachPhotosystem. Each molecule of oxygen released involves the flowof four electrons from two water molecules to two NADP+s andrequires four quanta of sunlight absorbed by each Photosystem toprovide the energy to do this. These are the "Light PhaseReactions" of photosynthesis, which produce two high energychemical products, namely NADPH and ATP.