BIOL 118 1st Edition Lecture 12 Outline of Last Lecture I Intro to Cell Division II Contrasting Mitosis and Meiosis III Functions of Cell Division IV What is a Chromosome V Chromosome Morphology Changes Before Mitosis VI Chromosome Replication VII The Cell Cycle VIII M Phase and Interphase IX Interphase S Phase X Interphase Gap Phases XI Mitosis Overview XII Chromosome Changes During Cell Cycle XIII Events in Mitosis XIV Prophase XV Prometaphase XVI Metaphase XVII Anaphase XVIII Telophase XIX Cytokinesis XX Cell Division XXI Different Cell Types Undergo Cell Division Differently Outline of Current Lecture I Photosynthesis a Two Linked Sets of Reactions b Nature of Light Energy c Photosynthetic Pigments Absorb Light d Role of Carotenoids and Other Accessory Pigments e Resonance f Reaction Center These 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 Centers h Electrons Participate in Redox Reactions i Chemiosmosis and Photophosphorylation j Oxygenic Photosynthesis k How Does Photosystem 1 Work l Summary of Photosystems m The Z Scheme n The Calvin Cycle and Carbon Fixation o The Calvin Cycle p The Importance of Rubisco q Connection to Global Warming Current Lecture Photosynthesis Requires sunlight carbon dioxide water Produces oxygen as a by product 6 CO2 12 H2O light energy C6H12O6 6 O2 6 H2O o Glucose C6H12O6 is usually the carbohydrate made through redox reactions o Carbon dioxide is reduced to glucose water is oxidized to oxygen Photosynthesis Two Linked Sets of Reactions Light dependent reactions o Produce O2 from H2O Calvin Cycle Reactions o Produce sugar from H2O The Nature of Light Energy Electromagnetic radiation is a form of energy Light o Type of electromagnetic radiation energy o Acts both particle like and wave like Photons o As a particle light exists in discrete packets o 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 light o Carotenoids Absorb blue and green light Reflect and transmit yellow orange red light The Role of Carotenoids and Other Accessory Pigments Carotenoids o Are accessory pigments that absorb wavelengths of light not absorbed by chlorophyll o Pass the energy on to chlorophyll Serve protective function as antioxidants in plants o High energy UV light can form free radicals o Carotenoids quench the free radicals by reducing them while carotenoids get oxidized Resonance 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 center Reaction 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 light o A transformation of electromagnetic energy into chemical energy Excited electrons in chloroplasts may o Drop back down to a low energy state causing fluorescence o Excite an electron in a nearby pigment inducing resonance o Be transferred to an electron acceptor in a redox reaction Two Types of Reaction Centers Light energy directly drives the removal of electrons from chlorophyll molecules Light reactions supply Calvin Cycle with ATP NADPH o Photosystem 1 Make NADPH o Photosystem 2 Make ATP Electrons Participate in Redox Reactions Electrons in the ETC o Participate in redox reactions o Gradually step down in potential energy These redox reactions result in o Protons being pumped from one side of the membrane to the other o Proton concentration inside the thylakoid increases 1000 fold Chemiosmosis and Photophosphorylation In the mitochondria protons diffuse down electrochemical gradient Chemiosmosis o Results when the flow of protons through ATP synthase causes a conformational change driving the phosphorylation of ADP Photophosphorylation o Capture of light energy by photosystem 2 to produce ATP How Does Photosystem 2 Obtain Electrons Photosystem 2 o Oxidizes water to replace electrons used during light reactions When excited electrons leave photosystem 2 enter the ETC o Photosystem becomes electronegative o Enzymes can remove electrons from water Leaving protons and oxygen Oxygenic Photosynthesis Photosystem 2 splits water replaces lost electrons produces oxygen o 2 H2O 4 H 4 e O2 This process is called oxygenic photosynthesis o 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 1 o Pigments in the antenna complex anchored in thylakoid membrane absorb photons o Pass the energy to the reaction center o 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 ferredoxin Summary of Photosystems Photosystem 2 produces o A proton gradient that drives the synthesis of ATP Photosystem 1 yields o Reducing power in the form of NADPH The Z Scheme Z Scheme a model of how photosystems 1 2 interact o Photon excites an electron in the pigment molecules of photosystem 2 s antenna complex o 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 product Calvin Cycle Carbon Fixation 2 Separate but linked processes in photosynthesis o The energy transformation of the light dependent reactions o The carbon dioxide reduction of the Calvin cycle In the presence of light o 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 independent o Require the ATP and NADPH produced by Calvin Cycle Carbon fixation All occur in the Calvin cycle o Carbon fixation o Oxidation of NADPH o Regeneration of CO2 acceptors RuBP o Consumption of ATP Calvin Cycle Has 3 phases o Fixation CO2 reacts with ribulose
View Full Document
Unlocking...