Comprehensive viewpoint on photosynthesis 2 pathways -light dependent reactions -light independent reactions Duality nature of light -wave and particle Photons -very fast moving packet of energy How does a molecule capture the energy of light? When a photon strikes a molecule, the energy coming from the photon is either loss as heat or absorbed the electrons of the molecule When it is absorbed, that energy will boost those electrons to higher energy levels Electrons occupies a discrete energy level in the orbit around the nuclei These electrons can go up or down What causes an electron in an atom to move a higher energy leverl? -when it undergoes excitation by an external energy gain na nakukuha from various mechanisms---heat, electron collision As these energy levels act as “stairs” There is just a right amount of energy exerted that is required to go to different energy levels Neither of the first 2 outcomes causes any change in the molecules sa 3rd, when absorbed, the photon will disappear but the energy will remain 1st law of thermodynamics: energy is not created nor destroyed When a molecule absorbs a photon, that molecule will acquire the energy from the photon ,, therefore it will be raised from ground state/lower energy to an excited state/higher energy Once na nagtranstion , this increase in energy boosts one electron into another shell that is farther from the nucleus within the molecule As the electrons goes farther from the nucleus mas nagiging less firmly held yung mga electrons, making it more chemically reactive Photosynthetic pigments -chemical compounds that reflect only certain light in the visible spectrum Nakikita naten sa plant ay reflected light Chlorophyll- green pigment, very common -absorbs all pigment of light except green We are capturing light through the excitation of the pigments Different pigments -flavanoids -caratenoids -antocyanin -phycovelins Pigments are not exclusive to plants alone but to other photosynthetic organisms Principal pigment -main photosynthetic pigment of a plant -acts as reaction centers Accessory Pigment -essential kasi they help in absorbing light,, and they deposit it to primary pigment -plants will be able to maximize the amount of photosynthesis they can do More pigment=more glucose/food for the plant High frequency=short wavelength Red=lower energy, bigger wavelength, lower frequency Violet= higher energy, shorter wavelength, higher frequency In the chloroplast, energy gets captured from sunlight and we store it by the use of atp and nadph while releasing oxygen and water and carbohydrates as products Thylakoids= pancake –like structures that are stacked -each house the photosynthetic pigments -contains the machinery in term of making atp -where photophosphorylation happen Yung mga pigments clustered together to form a photosytem Granum= whole column of thylakoids ,, grana in plural Stroma-semi liquid substance -can be compared to the cytosol of the cell -houses the enzymes needed to assemble organic molecules from c02 to produce atp and nadh and carbohydrates Lamella/lamellae- increase the efficiency of photosynthesis by keeping each granum at a distance so they do not clatter together -ensures that the maximum energy from sunlight is captured Photons get captured by chloropyll pigment are in a close proximity with each other Photosystem- functional structural unit of protein complexes wherein nakaembed yung chloropyl, carry out primary photochemistry of our photosynthesis -they absorb light and transfer energy and electrons to create atp and other organic molecules -acts as a large antenna that gathers all the light energy that are harvested by fifferent photosynthetic molecules When light strikes a pigment molecule in a photosystem, the resulting process is the excitation of the chlorophyll pigment Inde electrons yung napapasa but instead the energy is passed from one electron to another Until the energy arrives at a key chlorophyll molecule--- naggather ng energy from different chlrorophyl molecules--- siya magtatransfer ng energy as an excited electron to a specific primary electron acceptor 1st pathway: Ligh-depedendent reactions How do ligjt-dependent reactions occur during photosynthesis? Parts of photosystem 1. antenna complex- web of chlorophyll molecules that are linked together and held by the thylakoid membrane by a matrix of protein Potein matrix- light green, serves as the scaffold which holds the pigment together 2. Reaction center- transmembrane protein pigment complex, Chlorophyll a-acts as a trap for photon energy, they collect the energy that is passed through a primary electron acceptor This process is the key to converting light energy to chemical energy -this explains how we are transforming to chemical energy Electron donor = water Water will be oxidized, then the electron will go into the chlorophyll reaction center Kaya narerelease yung oxygen How do photosystems convert light to chemical energy? In bacteria, they only use single photosystem Cyclic photophosphorylation- only atp is produced, walang nadh Electron acceptor= Ferredoxin --- will transfer the electrons sa b6-f complex, when they receive the electrons, the electrons will enable the b6-f complex to pump protons in to the thylakoid that creates the proton motive force that will allow the creation of atp Plastocyanin- responsible to return back the electrons to the photosystems ---common sa photosynthetic bacteria Sa plants, gumagamit ng 2 photosystems Working together, they form a non-cyclic electron transfer/photophosphorylation How do the two photosystems of plants work together? Photsystem 2 yung nauuna in this process,,, -produces atp 4 electrons removed from 2 water molecules, The oxygen atoms will be released as heat Quinone molecule- primary electron acceptor Pag nareceive nya yung electron from ps2, marereduce siya kaya magiging plastoquinone siya ---final electron acceptor It will become a strong electron donor then it will pass the excited electron through the proton pump (b6-f complex)---- >closely the same with the bc-1 complex sa mithochondria The arrival of the energetic electron will cause the b6-f complex to pump a proton in the thylakoid space Then magkakaroon ng concentration gradient/ accumulation ng hydrogen ions that will enable the atp synthase to be powered,, para makapag produce ng atp Kaya kailangan yung mga complexes na daanana muna, kasi di kaya ng mga hydrogen ions na magdiffuse sa thylakoid membrane Yung mga electrons na mga pinasa ay mapupunta sa plastocyanin--→ magccary ng electrons sa ps1 Photosystem I -will accept the electron from plastocyanin, only if there is already a hole created by the exit of lightenergized electron--- in its higher energy level -does not rely on the quinons as an electron acceptor, but relies on ferrodoxin as its electron acceptor When electrons, gets pass on to ferrodoxin, the reduced ferodoxin now carries a high potential electron The electrons will be donated to nadp+ to produce nadph Nadph reductase,, nagkakaroon ulit ng proton gradient kaya magagmit ren sa creation ng atp at nadph Non-cyclic phosphorylation- The protons do not return but rather eneds up in nadp+ Most plants are incapable of short-circuiting the ps1 Yung excited electron minsasn bumabalik sa b6-f complex para gawing atp hindi nadph,, to create more atp Levels of atp and nadph indicated if cyclic or non cyclic How does the calvin cycle occur during photosynthesis in plants? Dark-reaction= calvin cycle= light-independent reaction -uses high energy coenzyme (atp and nadph) that are made from light-dependent reactions So that we can produce carbohydrates 1. carbon fixation Calvin cycle begins whenever a carbon atom from the co2 molecule is added to the 5-carbon molecule called RuBP------→nagpproduce ng isang unstable 6-carbon molecule na immediately nagssplit sa dalawang 3-carbon molecule (3PGA) Catalysed by Rubisco-most abundant protein in the world -pedeng oxigenase and carboxylase , can react with oxygen and carbon -can add carbon or can oxygen , these 2 reactions competes with each other Rubp reacting with CO2- normal process of photosynthesis in the calvin cycle Pero pag nagreact siya with oxygen,, nagiging competitor siya ng carbon dioxide Para icountereact yon to partially recover the carbon t, nagkaroon ng photorespiration--→ consumes the oxygen and releases carbon dioxide,, oxygen is being added to rubp to produce Phosphoglycorate Whenever photorespiration happens, it reduces the net crabon fix by the calvin cyle by 25 percent 3 molecules of CO2 and 3 molecules of R8BP--→ 6 molecules of 3PGA 2. reduction of 3gp to form glyceraldehyde-3-phosphate (g3p) Yung energy na galing kay atp at hydrogen galing sa nadph , gagamitin para idagdag sa 3PGA---→ G3P The reduced molecule G3pP will either combine to form glucose or ginagamit to make other molecules such as starch or fructose After the reduction, one phosphate group will be transferred to produce 6 ADP and 6 NADP+ that will be used again in the light-dependent reactions Last product= 6 molecule of G3P 1/6 of g3p lang used to make sugar, yung remaining 5 molecules will be used to produce RuMP (riboloze monophosphate) siya yung starting material para makabuo ulit ng RuBP Pero most of it ginagamit para sa regeneration of rubp 3. regeneration of the carbon dioxide acceptor, RuBP Si G3p will be used to produce Rubp For every 3 carbon dioxide molecules, 1 molecule of G3P leaves the cycle kasi kailangan siya sa formation ng glucose Tapos 5 yung kailangan sa production ng RuBP Products of the calvin cycle are crucial to the entire biosphere because they represent the total energy yield from harvesting light by photosynthetic organisms Pag masyadong mainit, sinara ng stoma yung pores nila para maprevent yung water loss, and nalilimit rin yung gas exchange Naddecrease yung carbon dioxide concentration kaya nagpproduce sa calvin cycle Common siya sa plants such as roses, wheat and rice ------they are called c3 plants,, dahil During carbon fixation, ang first product nila ay 3pga ---- common siya and may photorespiration C4 plants= But for plants like corn or sugar cane,grass, monocot,-- rate of photosynthesis nila di bumababa nor the photorespiration occurs,,, they do this by making a 4-carbon compound (oxaloacetate)- unang product nila - Very much may advantage sila kasi kahit isara yung stomata,hindi yun nakakaaffect sa rate of photosynthesis Photorespiration reduces the growth of our c3 plants,, kaya mas favoured yung c4 plants dahil mas favoured yung oxygen sa atmosphere naten ngayon CAM plants = ginagamit yung PEPC to produce oxaloacetate -they exhibit crassulacean acid metabolism -pineapple, bromilliasie, orchids, cactus, succulents -at night binubuksan nila yung stomata nila CO2 is fixed at night to forms to oxaloacetate Pag umaga, magoopen yung stomata, yung malic acid will undergo decarboxylation
