BIOL 225 Lecture 19.pdf - Graded In-class Group Activity...

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Unformatted text preview: 3/13/17 Graded In-class Group Activity • Wednesday, March 15, 2017 • If you miss class for a valid reason, you can arrange a make-up. Exam 1 • Available for pick-up outside my office, ISC 2117 • Answer key is posted in a folder under “Course Documents” Excerpts from Lecture 1 Tips for Success • Come to class • Take notes • Review your notes and the PowerPoint slides • Tell your friends what you’ve learned. • Read the textbook • Answer the in-text (blue-thread) questions while reading. Write out answers. Compare your answers with the answers in the back of the book. • Complete the end-of-chapter questions like you are taking a test (then check your answers). Lecture 19 Tips for Success, cont. • Get your money’s worth out of MasteringBiology! (e.g. in the Study Area, take practice tests, make flash cards, etc.) • Review homework in MasteringBiology, review In-Class Activities, review questions asked in class. Photosynthesis: Conversion of Light Energy into Chemical Energy BIOL 225 Prof. Liz Allison March 3, 2017 March 13, 2017 • Review and practice. A few days later review and practice again… 1 3/13/17 There would be no heterotrophs without autotrophs The Overall Process of Photosynthesis Light-capturing reactions 1. The Light-Capturing Reactions Light energy → Electrical energy The carbonfixing reactions (Calvin cycle) Electrical energy → Chemical energy Today LEONARD KOSCIANSKI Food Chain, Oil on Canvas, 46x66 in “What drives life is a little electric current, kept up by sunshine…” 2. The Carbon-Fixing Reactions (Calvin Cycle) Stored chemical energy is used to reduce carbon Lecture 20 This is the overall process. Today we are looking at the light capturing processes. It starts with water. Water is split and oxygen is output (measuring the creation of oxygen can give you the rate of light capture) The energy stored in the light capture is used to take CO2 into carbs. In this process ATP is hydrolyzed. H Photosynthesis occurs in the chloroplasts of green plants How do chloroplasts capture light energy? • Light acts like a The thylakoid membranes contain pigments Substances that absorb certain wavelengths of light Photosynthesis occurs in the chloroplasts of green plants. This is similar to mitochondria, where there are multiple mitochondria per cell. Chloroplasts have inner and outer membranes much like the mitochondria. particle (photon) and a wave. • Each photon or wavelength has a specific amount of energy. They capture it through pigments. Pigments are substances which absorb a particular pigment of light. A photon is a very specific unit of energy! 2 3/13/17 Isolating pigments via thin layer chromatography •What pigments are present? •What wavelengths do they absorb? • Cut out band • Extract pigment • Record wavelengths absorbed using a spectrophotom eter The question becomes: what pigments are present? Use a TLC to separate them. The absorption spectrum of pigments What color light do chlorophylls: ABSORB? TRANSMIT? A number of different pigments were found this way. The action spectrum for photosynthesis What wavelengths cause highest rates of photosynthesis ? Correlates with the absorption spectrum What color light do carotenoids: ABSORB? TRANSMIT? Green light is like being in the dark… Chlorophylls absorb in the purple and blue range, but reflect in the green range. Cartenoids are absorbing blueish violet, and transmitting in orange yellow region. The wavelength that is encouraging the highest level of photosynthesis corresponds to spectrophotometer data: meaning, the highest release is from blue and red. 3 3/13/17 Structures of Photosynthetic Pigments Carotenoids are accessory pigments • Absorb light and pass energy to chlorophyll What compound does this structure resemble? What properties of the tail help anchor it in the thylakoid membrane? The functional group changes from A to B chlorophyll. The ring structure resembles the hem group in the hemoglobin (Fe, iron, is what is held in the hem group. Look this up again). The tail helps to anchor the pigment into the thylakoid because it is hydrophobic. When pigments absorb light, electrons are boosted to a higher energy level Possible consequences: 1. Energy re-emitted as light energy of a longer wavelength plus heat = Fluorescence • Stabilize free radicals Xanthophylls Carotenes Carotenoids are less important. They pass their energy to chlorophyll rather than being used directly. They also help stabilize free radicals which can be generated from high energy light from the sun. They protect the plant from these dangerous frees. As the leaves stop making chlorophyll in the fall the carotenes are visible. There are two types of reaction centers: Photosystem I and photosystem II These photosystems work together to produce an enhancement effect In vitro 2. Electron at higher energy level is transferred to an electron acceptor In vivo Energy from the light is causing electrons to get boosted to a higher energy level. From there, the energy can be re-emitted as light energy of a longer wavelength plus heat as the electrons drop again. This only happens in vitro, because plants don't actually do this. This is not productive (can't use this for photosynthesis). In the cell, the boosted electron is passed to an acceptor in vivo, which is actually useful. In a plant the acceptors are within reaction centers: photosystem I and II. They maximize the total amount of energy that can be captured. They enhance each other. They both take a different type of red light (different wavelengths) 4 3/13/17 A closer look at Photosystem II… ATP synthase uses the proton-motive force to phosphorylate ADP Photophosphorylation: The capture of light energy by photosystem II to produce ATP *Compare with oxidative phosphorylation (Lecture 18) Photosystem II comes first. It strikes the antenna complex, the electron gets excited and is bounced from pigment to pigment until reaching the reaction center where it is caught by the carrier pheopytin, and passed onto a cytochrome complex. The names should be familiar from the ETC of respiration. The electrons are passed along the chain by a series of redox. There is a build up of H+ in the thylakoid lumen. this process is photophsophyrolation. This should be compared to oxidative phosphyrolation. The source of energy from OP is derived from the oxidation of glucose, vs the PP which is driven by the capture of light. Substrate level phosphyrlation is used to make ATP which can also compare. KEY POINTS Continuous flow of electrons: H20→PSII→PSI→NADP+ • Photophosphorylati on: ADP→ATP • Formation of NADPH Elections obtained by oxidizing (“splitting”) water Plants can consistently split water. From water all the way through the system, it becomes easier to follow. In this process, we get these two forms of stored energy: the ATP and NADPH. 5 3/13/17 Recommended reading from the textbook Chapter 10: p. 210-223, BioSkill 8: Spectrophotometry 6 ...
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