BIOL 118 1st Edition Lecture 12 Outline of Last Lecture I. Intro to Cell DivisionII. Contrasting Mitosis and MeiosisIII. Functions of Cell DivisionIV. What is a Chromosome?V. Chromosome Morphology Changes Before MitosisVI. Chromosome ReplicationVII. The Cell CycleVIII. M Phase and InterphaseIX. Interphase: S PhaseX. Interphase: Gap PhasesXI. Mitosis OverviewXII. Chromosome Changes During Cell CycleXIII. Events in MitosisXIV. ProphaseXV. PrometaphaseXVI. MetaphaseXVII. AnaphaseXVIII. TelophaseXIX. CytokinesisXX. Cell DivisionXXI. Different Cell Types Undergo Cell Division DifferentlyOutline of Current Lecture I. Photosynthesisa. Two Linked Sets of Reactionsb. Nature of Light Energyc. Photosynthetic Pigments Absorb Lightd. Role of Carotenoids and Other Accessory Pigmentse. Resonance f. Reaction CenterThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.g. Two Types of Reaction Centersh. Electrons Participate in Redox Reactions i. Chemiosmosis and Photophosphorylationj. Oxygenic Photosynthesisk. How Does Photosystem 1 Work?l. Summary of Photosystemsm. The Z Schemen. The Calvin Cycle and Carbon Fixationo. The Calvin Cyclep. The Importance of Rubiscoq. Connection to Global Warming Current LecturePhotosynthesis- Requires sunlight, carbon dioxide & water- Produces oxygen as a by-product- 6 CO2 + 12 H2O + light energy ®® C6H12O6 + 6 O2 + 6 H2Oo Glucose (C6H12O6) is usually the carbohydrate made through redox reactionso Carbon dioxide is reduced to glucose, water is oxidized to oxygenPhotosynthesis: Two Linked Sets of Reactions- Light-dependent reactionso Produce O2 from H2O- Calvin Cycle Reactionso Produce sugar from H2OThe Nature of Light Energy- Electromagnetic radiation is a form of energy- Lighto Type of electromagnetic radiation energyo Acts both particle-like and wave-like- Photonso As a particle, light exists in discrete packetso As a wave, light can be characterized by its wavelength The distance between 2 succesive wave crests Photosynthetic Pigments Absorb Light- Two major classes of pigments in plant leaves o Chlorophylls (alpha & beta) Absorb red and blue light Reflect and transmit green lighto Carotenoids Absorb blue and green light Reflect and transmit yellow, orange & red lightThe Role of Carotenoids and Other Accessory Pigments- Carotenoids o Are accessory pigments that absorb wavelengths of light not absorbed by chlorophyllo Pass the energy on to chlorophyll - Serve protective function as antioxidants in plantso High energy UV light can form free radicals o Carotenoids quench the free radicals by reducing them, while carotenoids get oxidizedResonance- The energy, but not the electron itself, is passed along to a nearby chlorophyll molecule, exciting another electron in that chlorophyll- Energy is transmitted from chlorophyll to chlorophyll until it reaches the reaction centerReaction Center- Transferred energy excites an electron in the reaction center chlorophyll- Excited electrons in the reaction center are passed to an electron acceptor in the reaction center- Reaction center pigments differ from antenna complex pigments in that RCP’s lose electrons when absorbing lighto A transformation of electromagnetic energy into chemical energy- Excited electrons in chloroplasts mayo Drop back down to a low energy state, causing fluorescenceo Excite an electron in a nearby pigment, inducing resonanceo Be transferred to an electron acceptor in a redox reactionTwo Types of Reaction Centers- Light energy directly drives the removal of electrons from chlorophyll molecules- Light reactions supply Calvin Cycle with ATP & NADPHo Photosystem 1: Make NADPHo Photosystem 2: Make ATPElectrons Participate in Redox Reactions- Electrons in the ETCo Participate in redox reactionso Gradually step down in potential energy- These redox reactions result ino Protons being pumped from one side of the membrane to the othero Proton concentration inside the thylakoid increases 1000-foldChemiosmosis and Photophosphorylation- In the mitochondria, protons diffuse down electrochemical gradient- Chemiosmosiso Results when the flow of protons through ATP synthase causes a conformational change, driving the phosphorylation of ADP- Photophosphorylationo Capture of light energy by photosystem 2 to produce ATPHow Does Photosystem 2 Obtain Electrons?- Photosystem 2o Oxidizes water to replace electrons used during light reactions- When excited electrons leave photosystem 2 & enter the ETCo Photosystem becomes electronegativeo Enzymes can remove electrons from water Leaving protons and oxygenOxygenic Photosynthesis- Photosystem 2 splits water replaces lost electrons & produces oxygen o 2 H2O ® 4 H+ + 4 e– + O2- This process is called oxygenic photosynthesiso Photosystem 2 is the only protein complex able to oxidize water in this way- The oxygen released from oxygenic photosynthesis was critical to the evolution of life as we know it- O2 was almost nonexistent on Earth before enzymes evolved that could catalyze the oxidation of water How Does Photosystem 1 Work?- Photosystem 1o Pigments in the antenna complex, anchored in thylakoid membrane, absorb photonso Pass the energy to the reaction centero Ultimate result is to reduce NADP+ to NADPH as follows: Excited electrons from the reaction center are passed down an ETC of iron & sulfur containing proteins to ferredoxinSummary of Photosystems- Photosystem 2 produceso A proton gradient that drives the synthesis of ATP- Photosystem 1 yieldso Reducing power in the form of NADPHThe Z Scheme- Z Scheme: a model of how photosystems 1 & 2 interacto Photon excites an electron in the pigment molecules of photosystem 2’s antenna complexo Resonance occurs until the energy reaches the reaction center The electrons of photosystem 2 will be replaced by electrons stripped from water, producing oxygen gas a by-productCalvin Cycle & Carbon Fixation- 2 Separate, but linked processes in photosynthesis:o The energy transformation of the light dependent reactionso The carbon dioxide reduction of the Calvin cycle- In the presence of lighto ATP & NADPH are produced by photosystems 1 & 2 fuel the Calvin cycle- The reactions that produce sugar from carbon dioxide in the Calvin cycle are light independento Require the ATP and NADPH produced by Calvin Cycle & Carbon fixation- All occur in the Calvin cycle:o Carbon fixationo Oxidation of NADPHo
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