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Topic: Light reactions

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Photosystem II

Electron transport chain

Photosynthesis

Dark reaction

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	Biology 2402 Lecture Notes - Photosynthesis Part 1. The Light Reactions
		Light is a paradoxical entity since, as the field of quantum mechanics has shown, it has both wave-like and particle-like properties.
		The region of 400 to 700 nm is the predominant waveband that reaches the surface of the Earth.
		The reaction center chlorophyll undergoes charge separation when it is elevated to the excited state by the absorption of a photon.
	www.ualr.edu /botany/lightrxns.html (1885 words)

	HORT 301 - Light Reactions of Photosynthesis (Site not responding. Last check: 2007-10-17)
		The absorbed light energy is used to power the transfer of electrons between a series of compounds localized in the thylakoid membranes that serve as electron donors and acceptors.
		The energy produced by the light reactions is used to fuel the dark reactions that reduce carbon dioxide to carbohydrate.
		In plant physiology the quantity of light is often expressed as the number of photons in the wavelength region from 400 to 700 nm.
	www.hort.purdue.edu /hort/courses/HORT301/PHOTO/Intro.htm (388 words)

	Solar Powered Reactions, Modifying Proteins for Novel Photochemistry (Site not responding. Last check: 2007-10-17)
		A wide range of reactions are efficiently catalyzed by proteins, a few of which utilize light to drive oxidation/reduction or other chemical reactions.
		Using site-directed mutagenesis, Williams, Allen and coworkers have found that the potential of the primary donor is strongly dependent upon the number of hydrogen bonds formed between the donor and the protein (15,16).
		In the bacterial reaction center, the primary donor oxidizes a cytochrome that is bound through salt bridges formed between carboxylates on the reaction center surface and lysine residues on the cytochrome surface.
	photoscience.la.asu.edu /bionano/research3.htm (1344 words)

	Re: Disucss the chloroplast structure and light reactions of photosynthesis.
		The thylakoid membranes are the sites of the photosynthetic light reactions: the harvesting of sunlight, transport of electrons and synthesis of ATP (the energy currency of living organisms).
		The pigment/proteins are arranged in light harvesting complexes that absorb light and pass the light energy from pigment to pigment molecule to special chlorophyll molecules that are known as the photosynthetic reaction centers.
		Light reactions: The energy transferred to the reaction centers excite (activate) the chlorophylls and cause them to give up electrons and pass them to other electron carriers (i.e.
	www.madsci.org /posts/archives/feb99/919311920.Gb.r.html (732 words)

	Photosynthesis (Site not responding. Last check: 2007-10-17)
		The light reactions and the Calvin cycle cooperate in converting light energy to the chemical energy of food
		Thus, light energy is initially converted to chemical energy in the form of two compounds: NADPH, a source of energized electrons ("reducing power"); and ATP, the versatile energy currency o that the light reactions produce no sugar; that happens in the second stage of photosynthesis, the Calvin cycle.
		An Overview of photosythesis: cooperation of the light reactions and the Calvin cycle.
	www.calpoly.edu /~spuhl/p3.html (556 words)

	Light Reactions (Site not responding. Last check: 2007-10-17)
		When a photon of light strikes a pigment molecule, the energy is passed from molecule to molecule until it reaches the reaction center which contains a particular form of chlorophyll a.
		The reaction-center chlorophyll of photosystem I is known as P700 because this pigment is best at absorbing light having a wavelength of 700 nm (the far-red part of the light spectrum).
		An incidental by-product of the light-dependent reactions is oxygen.
	www.bio.umass.edu /biology/conn.river/light.html (282 words)

	PHOTOSYNTHESIS REVIEW QUESTIONS
		This energy may come from light (as in the light reactions of photosynthesis) or from the breakdown of sugars (as in cellular respiration).
		The wavelengths of light that are visible to humans range from approximately 400 nanometers (violet) to 700 nanometers (red).
		Light energy is absorbed by electrons that supply energy for the formation of molecules of ATP and NADP-H which are used as temporary energy storing molecules.
	www.utm.edu /departments/cens/biology/faculty_pages/photosyn.htm (1602 words)

	LIGHT REACTIONS
		A photosystem is a complex of pigments designed to gather light energy and pass it on to the P680 or the P700 molecule.
		Light energy may be directly absorbed by the P700 or P680 reduced molecule.
		The scenario is the same: energy transfer from one carotinoid to the next eventually passing the energy on to a chlorophyll which passes energy from chlorophyll to chlorophyll until the energy eventually reaches P680 or P700.
	www.mrs.umn.edu /~goochv/CellBio/lectures/lightrxn/lightrxn.html (1164 words)

	light reactions
		The purpose of these photo systems is to collect energy over a "broad" range of wavelengths and concentrate it to one molecule called a reaction center which uses the energy to pass one of its electrons on to a series of enzymes.
		The reaction center is then able to get rid of the energy by passing the energy and its e- onto a series of enzymes.
		An e- and its energy are accepted by P700 and are passed to a series of enzymes that couple oxidation-> reduction reaction (the passing of an e- from one molecule to another with a higher affinity for e-) to the transport of protons from the stroma into the thylakoid space.
	www2.mcdaniel.edu /Biology/botf99/photo/l4ightrx.html (1157 words)

	Biology Review 3
		Light is absorbed by chlorophyll a which "excites" the electrons in the chlorophyll molecule.
		Energy from the light reaction is used to convert carbon dioxide into a series of carbon sugars.
		The reactions require energy from ATP, hydrogen, and electrons from NADPH, and carbon and oxygen from carbon dioxide, which is present in the air or water that surrounds photosynthetic cells.
	www.utdallas.edu /~msweet/bio3.htm (1931 words)

	BCH/PPA 503 \| Lecture Two Web Notes
		Carbon fixation uses ATP and NADPH generated from the light reactions of photosynthesis to "fix" CO into the hexose sugar, glucose.
		Reactions 1 through 15 constitute the cycle that culminates in the formation of one equivalent of glucose.
		on the 2,3-enediol intermediate and is hypothesized to be an inevitable consequence of the reaction mechanism of RUBISCO.
	www.uky.edu /~dhild/biochem/2/lect.html (879 words)

	KE0026 Biochemistry Lectures
		In the light reactions, water is split, oxygen gas is released, and NADPH and ATP is produced.
		In the Calvin cycle, (dark reactions) carbon dioxide is converted (fixed) to carbohydrate by using NADPH and ATP produced in the light reactions.
		Light is primarily absorbed by chlorophylls and carotenoids in light harvesting complexes and then rapidly transferred to a reaction centre where charge separation occurs.
	xray.bmc.uu.se /Courses/Bke1/Lectures/photosynthesis1.html (234 words)

	Photosynthesis and Respiration
		First the Light Reactions, and requires the direct energy of light to make energy carrier molecules that are used in the second process.
		White light is separated into the different colors (wavelengths) of light by passing it through a prism(learned in 8th grade science).
		In 1905 Albert Einstein developed a theory that light was composed of particles, photons, whose energy is inversely proportional to the wavelength of the light.
	members.tripod.com /bemace/project.html (524 words)

	Botany online: Photosynthesis - Dark Reactions - Assimilation - Carbon Dioxide - Calvin Cycle
		The Dark Reactions of Photosynthesis, Assimilation of Carbon Dioxide And The CALVIN Cycle.
		This reaction is catalyzed by ribulose bisphosphate carboxylase (also called Rubisco or, formerly, fraction-1-protein), as far as quantity is concerned the most common protein of the world.
		The reverse reaction occurs, too, in glycolysis though in photosynthesis NADP is needed instead of the NAD consumed during glycolysis.
	www.biologie.uni-hamburg.de /b-online/e24/24a.htm (741 words)

	Photosynthesis 1
		This is essentially the same phenomenon as a neon light, except the electrons of neon gas molecules in the glass tube become excited and then release their energy as a white glow.
		The light reactions of photosynthesis occur in the grana.
		Leaves generally appear green because wavelengths of light from the red and blue regions of the visible spectrum are necessary to excite the chloroplast electrons, and unused green light is reflected.
	waynesword.palomar.edu /photsyn1.htm (2395 words)

	Lecture 6
		In 1905, it was shown that the changes in temperature and light intensity had both an individual and combined effect on the rate of photosynthesis.
		The light is absorbed by the pigment molecules.
		Light energy enters PII where it is trapped by the P680 reaction center.
	forest.mtu.edu /classes/fw3020/lectur5.htm (1052 words)

	BB 350 Oregon State University (Site not responding. Last check: 2007-10-17)
		In the light reactions of photosyntheis, 1) electrons are removed from water (producing oxygen); 2) ATP is produced by the process of photophosphorylation as electrons pass through the membrane of the thylakoids; and 3) NADPH is produced from NADP+ in the final reduction reaction.
		Thus, we can think of the light reactions as the ones where the energy necessary for making glucose is stored up (charging a battery) and the dark reactions as the ones that use energy from the light reactions to store that energy in another form - glucose.
		The dark reactions of photosynthesis are also known as the Calvin cycle in honor of their discoverer, Melvin Calvin.
	oregonstate.edu /instruction/bb350/highlightsphotosynth.html (800 words)

	Botany online: Photosynthesis - Light Reactions
		This attempt proved to be insufficient for the light reactions.
		It does never reach the reaction centre and is emitted as warmth or light (red autofluorescence of chlorophyll).
		The reaction centre of every photosystem is represented by one molecule of chlorophyll a each (P 700 in PS I and P 680 in PS II, where P means pigment).
	www.biologie.uni-hamburg.de /b-online/e24/24c.htm (1605 words)

	Nobel Prize in Chemistry 1961 - Presentation Speech
		The energy needed for the synthesis is supplied by light which is absorbed by the organisms and subsequently converted by them from light energy into chemical energy.
		The sequence of reactions by which carbon dioxide and water are converted to carbohydrate is called carbon dioxide assimilation or, taking into account the role of light energy, photosynthesis.
		This means that light energy is not directly involved in the reactions of assimilation; light energy is used for regeneration of co-factors which are consumed in the assimilation reactions.
	nobelprize.org /nobel_prizes/chemistry/laureates/1961/press.html (996 words)

	[No title] (Site not responding. Last check: 2007-10-17)
		Light energy is transfered to a chlorophyll electron, exciting it to a higher energy level.
		Interdependence of the light reactions and the Calvin cycle
		The reactions of the Calvin cycle are not directly dependent on light, but they usually do not occur at night.
	shakti.trincoll.edu /~odonnell/153/LectureStuff/PhotosynthesisI.html (565 words)

	PHOTOSYNTHESIS
		Chlorophyll only triggers a chemical reaction when it is associated with proteins embedded in a membrane (as in a chloroplast) or the membrane infoldings found in photosynthetic prokaryotes such as cyanobacteria and prochlorobacteria.
		Recent evidence suggests that a major enzyme of the Dark Reaction is indirectly stimulated by light, thus the term Dark Reaction is somewhat of a misnomer.
		Light energy causes the removal of an electron from a molecule of P680 that is part of Photosystem II.
	www.emc.maricopa.edu /faculty/farabee/BIOBK/BioBookPS.html (4314 words)

	Photosynthesis: The Role of Light
		Light is absorbed by the antenna pigments of photosystems II and I.
		Like the photocell in a light meter, photosystem I is simply using light to create a flow of current.
		The entire complex ensures that most of the energy of light will be trapped and passed on to the reaction center chlorophylls.
	users.rcn.com /jkimball.ma.ultranet/BiologyPages/L/LightReactions.html (1142 words)

	The Light Reactions of Photosynthesis
		The energy of light captured by pigment molecules, called chlorophylls, in chloroplasts is used to generate high-energy electrons with great reducing potential.
		The light reactions of photosynthesis use energy from photons to generate high-energy electrons (Figure 19.2).
		In the dark reactions, the NADPH and ATP formed by the action of light drive the reduction of CO to more-useful organic compounds.
	www.ncbi.nlm.nih.gov /books/bv.fcgi?rid=stryer.chapter.2660 (523 words)

	Impact of Wavelength on Photosynthetic Rate in Arabidopsis thaliana
		I believed this because these photosynthetic pigments would absorb the light energy and use it to drive the light reactions of photosynthesis, which would in turn produce molecules to drive the Calvin cycle of carbon fixation--and growth.
		It must be emphasized, thus, that my findings reflect data for particular wavelengths of light (see chart) under each chamber, which may or may not be in accord with the designated "color" of the box.
		For instance, this means that although it appears that the plants under the purple chamber had the highest rate of growth, the purple wavelengths of light did not drive photosynthesis particularly efficiently.
	www.sidwell.edu /us/science/vlb5/Independent_Research_Projects/dwinik (667 words)

	The Photosynthetic Process
		Therefore, there are two basic parts to photosynthesis, the light reactions (which are light dependent) and the light independent reactions (or dark reactions).
		One can think of the light dependent reactions as a way to increase the free energy of the system and the light independent reactions as a way to convert that new free energy into the bonds of glucose.
		When a chlorophyll molecule in the thylakoid membrane is excited by light, the energy level of an electron in its structure is boosted by an amount equivalent to the energy of the absorbed light and the chlorophyll becomes excited.
	io.uwinnipeg.ca /~simmons/cm1503/lightreact.htm (605 words)

	The Light Reactions of Photosynthesis
		All the reactions of photosynthesis that are directly dependent upon light are known as the
		The light reactions occur in the part of the cell known as the
		The purpose of the light reactions is to convert light energy into chemical energy in the form of ATP and NADPH.
	ghs.gresham.k12.or.us /science/ps/sci/soph/energy/photosyn/lightrxns.htm (97 words)

	[No title]
		All the reactions of photosynthesis that are directly dependent upon light are known as the light dependent reactions.
		The light dependent reactions occur in the part of the cell known as the thylakoids (Stacks of thylakoids are known as grana.).
		One entirely new feature is the position, and a tentative structure, of the Mn-complex central to the water oxidizing reactions, and the positions of the redox-active tyrosines.
	www.lycos.com /info/photosynthesis--reactions.html (470 words)

	ODU Biology 108N: Photosynthesis - Dark Reactions
		from the time it was produced in the light reactions, through the carrying of the hydrogen to the dark reactions, and the final use of the hydrogen to make a carbohydrate molecule.
		These molecules are formed during the (light/dark) reactions, and their energy is released during the (light/dark) reactions.
		Both the light and dark reactions can work independently of one another; however, the dark reactions do require ATP and NADPH which may be formed during the light reactions.
	www.lions.odu.edu /~knesius/miniunits/epsilon/epsilon12.html (3034 words)

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