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Bio 211 Day 10 Today • How Do Cells Obtain Energy? • What Happens During Glycolysis? • What Happens During Cellular Respiration? • What Happens During Fermentation? • How does photosynthesis work? Participation • Tell me everything you know about photosynthesis… • Compare with a friend Figure 8-1 Photosynthesis provides the energy released during glycolysis and cellular respiration energy from sunlight Most of life could be summarized as: Creating sugar And then Oxidizing sugar photosynthesis 6 CO2 6 H2O 6 O2 cellular respiration C6H12O6 glycolysis ATP Breaking down glucose is photosynthesis backwards Photosynthesis 6 CO2 6 H2O light energy C6H12O6 6 O2 Complete glucose breakdown C6H12O6 6 O2 6 CO2 6 H2O ATP heat (cytosol) A respiration summary 1 glucose Glycolysis glycolysis Glucose (6C) 3GP 2x pyruvate (3C) ATP 2 lactate fermentation 2 pyruvate If O2 is available If no O2 is available 2 ethanol 2 CO2 6 O2 2C + 4C 4C CO2 & electrons on NADH Electron transport chain electron transfer O2 H2O proton gradient used to make ATP requires ATP synthase Photosynthesis summary cellular respiration 6 CO2 Kreb’s cycle Light reactions – pigments, ETCs ATP H2O split by photons O2 + electrons high energy electron transfer NADPH proton gradient used to make ATP requires ATP synthase 6 H2O Dark reactions – “Calvin cycle” CO2 3C G3P glucose mitochondrion Let’s review glycolysis • Which of these goes in and which comes out? • ATP • NADH • NAD+ • Glucose • pyruvate Let’s review glycolysis • INPUT vs OUTPUT • ATP • NADH • NAD+ - reduced to NADH • Glucose - oxidized • pyruvate One more thing… G3P The essentials of glycolysis Fig. 8-3 Figure 8-4 A mitochondrion LABEL ME!! Figure 8-4 A mitochondrion matrix inner membrane intermembrane space outer membrane Figure 8-5 Reactions in the mitochondrial matrix Formation of acetyl CoA coenzyme A 3 NADH 3 NAD CO2 FADH2 coenzyme A acetyl CoA pyruvate NAD FAD Krebs cycle NADH ADP ATP Krebs cycle • acetyl CoA + 4C molecule 6C citrate coenzyme A is released – where does it go? • Series of enzymes 2C acetyl 2 CO2 • 4C molecule is regenerated Where do the electrons go next? Where do the carriers drop their cargo? • NADH • FADH2 Electron transport chain: proton pumps Per NADH, protons are in 3 places Per FAD, protons pumped in 2 places Figure 5.16 Chemiosmosis Proton flow through ATP synthase turns its turbine; mechanical energy used to power ATP synthesis from ADP and Pi Figure 5.15 1. Do prokaryotes (bacteria) perform cellular respiration? YES… and BTW why should we care? Because of ecology, medicine, industry, science Diagram of aerobic respiration • Draw a eukaryotic cell with a mitochondrion • Where are • Glycolysis • Kreb’s cycle • Electron transport chain Where do these reactions happen? Pathway Glycolysis Intermediate step Krebs cycle ETC Eukaryote Prokaryote Where do these reactions happen? Pathway Eukaryote Prokaryote Glycolysis cytoplasm Cytoplasm Intermediate step Mitochondrial matrix Cytoplasm Krebs cycle Mitochondrial matrix Cytoplasm ETC Inner mitochondrial membrane Plasma membrane 2. What if there is no oxygen? • Typical textbook says: • Without oxygen, electrons stop moving through ETC, H is not pumped across the inner membrane • The H gradient dissipates, and ATP synthesis by chemiosmosis stops • ATP generation continues only when there is a steady supply of oxygen • Is this true? • This is true in most tissues in our bodies but NOT in all living things… some bacteria Two anaerobic processes • Anaerobic respiration • Fermentation • Are they the same thing?? Can prokaryotes do respiration? • Yes some of them can! • Some do aerobic respiration • Some do anaerobic respiration • WAIT… but do they have mitochondria?? Respiration by cell type • Eukaryotes • Where is the ETC? • Which part of mitochondrion is acidic • How much ATP per glucose? • Prokaryotes • • • • Where is the ETC? Where do the protons go? How much ATP per glucose? Why is it more? Respiration by cell type • Eukaryotes • Where is the ETC? Inner mito membrane • Which part of mitochondrion is acidic? Intermembrane space • How much ATP per glucose? Textbooks 32-36 • Prokaryotes • • • • Where is the ETC? Where do the protons go? How much ATP per glucose? 34-38 Why is it more? Chapter 7 Photosynthesis What is photosynthesis? Capturing solar energy used for? Making sugar!! What is the energy Figure 8-1 Photosynthesis provides the energy released during glycolysis and cellular respiration energy from sunlight Most of life could be summarized as: Creating sugar And then Oxidizing sugar photosynthesis 6 CO2 6 H2O 6 O2 cellular respiration C6H12O6 glycolysis ATP Chapter 7 topics • What Is Photosynthesis? • How is light energy converted to chemical energy? (the “light reactions”) • How is chemical energy stored in sugar? (Calvin cycle aka “dark reactions”) What Is Photosynthesis? • For most organisms, energy is derived from sunlight, either directly or indirectly • DIRECT: Trap sunlight using photosynthesis • Photosynthesis - solar energy is converted to chemical energy – trapped and stored in the bonds of sugar • INDIRECT: Organisms that cannot directly trap sunlight get their energy from where? Special equipment – the solar panel • Leaves are structures adapted for photosynthesis • Photosynthesis in plants takes place in chlorophyll-containing organelle, the _______,usually in leaf cells • Chloroplasts perform chemical reactions to convert energy from ________ into stored energy in sugar • Will all parts of a plant contain chloroplasts? Figure 7-1 An overview of photosynthetic structures cuticle upper epidermis mesophyll cells Leaves stoma stoma bundle sheath cells vascular bundle (vein) outer membrane inner membrane thylakoid stroma Chloroplast lower epidermis chloroplasts Internal leaf structure channel interconnecting thylakoids Mesophyll cell containing chloroplasts Leaf surface anatomy • Epidermis • upper and lower surfaces of a leaf consist of a layer of transparent cells, the epidermis • Cuticle • The outer surface of both epidermal layers is covered by a transparent, waxy, waterproof layer to reduce the evaporation of water from the leaf • Stomata/stoma • Leaves obtain CO2 for photosynthesis from the air through pores in the epidermis called stomata (stoma) Figure 7-2 Stomata Stomata open Stomata closed Figure 7-1 An overview of photosynthetic structures A B mesophyll cells Leaves stoma C D outer membrane inner membrane thylakoid stroma Chloroplast chloroplasts bundle sheath cells vascular bundle (vein) Internal leaf structure channel interconnecting thylakoids Mesophyll cell containing chloroplasts Inside the leaf • Mesophyll • layers of cells inside the leaf where the chloroplasts are located and photosynthesis occurs • Chloroplasts • Where _______ takes place in plants - most of these organelles are found in mesophyll cells Figure 7-1 An overview of photosynthetic structures cuticle upper epidermis A Leaves stoma stoma bundle sheath cells vascular bundle (vein) outer membrane inner membrane thylakoid stroma B lower epidermis chloroplasts Internal leaf structure channel interconnecting thylakoids Mesophyll cell containing chloroplasts Chloroplast anatomy • double membrane enclosing a fluid called stroma • Embedded in the stroma are disk-shaped membranous sacs called thylakoids • The “light reactions” of photosynthesis occur in and adjacent to the membranes of the thylakoids • The “dark reactions” – Calvin cycle – take place in the stroma photosynthesis • Starting with carbon dioxide (CO2) and water (H2O), photosynthesis converts sunlight energy into chemical energy stored in bonds of glucose and releases oxygen (O2) as a product by the following equation: 6 CO2 6 H2O light energy C6H12O6 6O2 carbon water sunlight glucose oxygen dioxide (sugar) Does this entire process require sunlight? What are the “light” reactions? And the “dark”? Light vs dark – how are they related? Figure 7-3 An overview of the relationship between the light reactions and the Calvin cycle H2O 6 6 CO2 energy from sunlight ATP light reactions NADPH Calvin cycle ADP NADP thylakoid sugar (stroma) chloroplast O2 C6H12O6 Light reactions • light reactions: chlorophyll and other molecules embedded in the chloroplast thylakoid membranes capture sunlight energy and convert some of it into chemical energy stored in the energy-carrier molecules ATP and NADPH Calvin cycle • In the reactions of the Calvin cycle, enzymes in the stroma use CO2 from the air and chemical energy from the energy-carrier molecules to synthesize a three-carbon sugar that will be used to make glucose Photosynthesis is the sum of BOTH light and dark reactions • The “photo” part of photosynthesis refers to the capture of sunlight in the thylakoid membranes • The “synthesis” part of photosynthesis refers to the Calvin cycle, which synthesizes sugar from the energy captured in ATP and NADPH in the light reactions How Is Light Energy Converted to Chemical Energy? • Convert energy of sunlight to chemical energy in ATP and NADPH • Light reaction machinery is anchored within the membranes of the thylakoid What is light? • The sun emits energy • a broad spectrum of electromagnetic radiation • This electromagnetic spectrum ranges from waves, to infrared, visible, UV, & gamma rays --------- short) • Wavelength of light • inversely related to strength • Long wavelength (radio) versus short wavelength (gamma) radio (long ------------------------ Electromagnetic (EM) spectrum Capturing light with pigments • Light is made of photons • individual packets of energy • Wavelength of light • Size inversely related to strength • Gamma rays are ____ so that makes them strong/weak? • radio waves are big/small? so they are _____ • Visible light • Wavelength strong enough to alter pigment – eg. chlorophyll a • Chlorophyll a • Main light-capturing pigment in chloroplasts • absorbs violet, blue, and red light • Green light is reflected, which is why leaves appear green Is chlorophyll alone? • accessory pigments in chloroplasts • absorb more wavelengths of light and transfer them to chlorophyll a • Chlorophyll b • absorbs blue and red-orange wavelengths of light (missed by chlorophyll a) • Carotenoids • absorb blue and green light, and appear yellow or orange to our eyes bc they reflect these colors • Why do the leaves turn?? • In autumn, green chlorophyll breaks down before the carotenoids do, revealing their yellow color Figure 7-4 Light and chloroplast pigments light absorption (percent) 100 chlorophyll b 80 carotenoids 60 chlorophyll a 40 20 0 wavelength (nanometers) 400 450 gamma rays 500 550 600 visible light X-rays UV higher energy 650 700 750 micro- radio infrared waves waves lower energy Figure 7-5 Loss of chlorophyll reveals carotenoid pigments Where do the light reactions happen? • In association with the thylakoid membranes • The thylakoid contain photosystems, • a cluster of chlorophyll and accessory pigment molecules surrounded by various proteins • Two photosystems • photosystem II (PS II) and photosystem I (PS I), work together during the light reactions Light reactions – the machinery • Each photosystem has a unique electron transport chain nearby embedded in the thylakoid membrane • Within the thylakoid membrane, electron path is: PS II ETC II PS I ETC I NADP Light reactions – absorbing light The reaction center within each photosystem consists of a pair of specialized chlorophyll a molecules and a primary electron acceptor molecule embedded in a complex of proteins 1. Photons of light are absorbed by pigment in photosystem II --> electrons are energized 2. The energized electron is ejected from the chlorophyll and recaptured by the primary electron acceptor Light reactions – creating a gradient Photosystem II uses light energy to create a hydrogen ion gradient and split water 3. The electron from PS II is passed down the ETC losing energy at each step 4. This energy is used to pump hydrogen ions (H) across the thylakoid membrane into thylakoid space, where it will be used to generate ATP (see later) Light reactions – two photosystems Photosystem I is actually the second system 5. The energy-depleted electron leaves ETC II and enters the reaction center of PS I, where it replaces an electron ejected when light strikes photosystem I 6. Light energy striking PS I is captured by its pigment molecules and funneled to a chlorophyll a molecule in the reaction center 7. This ejects an energized electron that is picked up by the primary electron acceptor of PS I Light reactions gradient Photosystem I also has a ETC 8. From the primary electron acceptor of PS I, the energized electron is passed along ETC I until it reaches NADP 9. The energy-carrier molecule NADPH is formed when each NADP molecule picks up two energetic electrons, along with one hydrogen ion Animation: Photosynthesis—Light-Dependent Figure 7-6 Energy transfer and the light reactions of photosynthesis H2O CO2 ATP light reactions Calvin cycle NADPH ADP NADP sugar O2 C6H12O6 high e electron transport chain I e e primary electron acceptor NADPH NADP energy level of electrons e e light energy electron transport chain II pigment molecules e ATP reaction center chlorophyll a molecules Photosystem II e low 2 H H2O ½ O2 Photosystem I H OK so why did we make a gradient? • The H+ gradient generates ATP by chemiosmosis Chemiosmosis??? • three steps 1. As the energized electron travels along ETC, the energy it loses is used to pump hydrogen ions into the thylakoid space 2. High concentration H inside the space relative to the surrounding stroma creates a gradient Where do the H+ ions want to go? Can they? 3. H flows down its concentration gradient through a thylakoid channel protein called ATP synthase, generating ATP from ADP Figure 7-7 Events of the light reactions occur in and near the thylakoid membrane thylakoid chloroplast (stroma) light energy CO2 H is pumped into the thylakoid space H electron transport chain I electron transport chain II e H e Calvin cycle NADP NADPH sugar e e C6H12O6 ATP synthase e ADP e photosystem II 2 H H2O ½ (thylakoid space) O2 H Pi photosystem I H H H H H A high H concentration is created in the thylakoid space H H thylakoid membrane The flow of H down its concentration gradient powers ATP synthesis ATP Bio 211 D10 part 2 So we got through the “light reactions” – what’s next? • Let’s finish photosynthesis! – DARK REACTIONS – “Calvin cycle” The Calvin Cycle: how is ATP used to make sugar? • Starting material: • what’s in sugar? how do we get those atoms? • Carbon dioxide and water sugar • What kind of reaction is this? • Where does the energy come from? • Where does this happen? The Calvin Cycle: how is ATP used to make sugar? • Starting material: • what’s in sugar? how do we get those atoms? • Carbon dioxide and water sugar • What kind of reaction is this? • Where does the energy come from? • ATP and NADPH synthesized from light reactions are used to power the synthesis of a simple sugar (gyceraldehyde-3-phosphate, or G3P) • Where does this happen? • This is accomplished through a series of reactions occurring in the stroma called the Calvin cycle Steps in the Calvin cycle • Three steps 1. Carbon fixation 2. The synthesis of G3P 3. The regeneration of ribulose bisphosphate (RuBP) Figure 7-9 The Calvin cycle fixes carbon from CO2 and produces the simple sugar G3P H2O CO2 ATP light reactions Calvin cycle NADPH ADP NADP sugar O2 C6H12O6 Carbon fixation combines three CO2 with three RuBP using the enzyme rubisco 3 CO2 6 3 PGA RuBP Calvin cycle 3 6 ATP 6 ADP ADP 6 NADPH 3 ATP 6 NADP 5 6 G3P Using the energy from ATP, the five remaining molecules of G3P are converted to three molecules of RuBP G3P Energy from ATP and NADPH is used to convert the six molecules of PGA to six molecules of G3P 1 G3P One molecule of G3P leaves the cycle 1 1 G3P Two molecules of G3P combine to form glucose and other molecules 1 G3P glucose Let’s walk through them shall we? • Three steps 1. Carbon fixation 2. The synthesis of G3P 3. The regeneration of ribulose bisphosphate (RuBP) Step one: carbon fixation 1. Carbon fixation • CO2 is incorporated, or “fixed,” into a larger organic molecule • enzyme rubisco combines three CO2 molecules with three RuBP (ribulose bisphosphate) molecules, forming three unstable 6carbon molecules that each quickly split in half • Six molecules of a 3-carbon product, phosphoglyceric acid (PGA), result • Making 3-carbon PGA molecule is called the C3 pathway Step two: G3P synthesis 2. Uses energy of ATP and NADPH (generated by light reactions) • Converts six PGA molecules into six of the 3-carbon sugar molecule G3P (glyceraldehyde 3 phosphate) Step three: RuBP 3. The regeneration of RuBP • ATP from the light reactions is used with five of the six G3P molecules formed to regenerate the 5-carbon RuBP necessary to repeat the cycle • The remaining G3P molecule, which is the end product of photosynthesis, exits the cycle Animation: Light-Independent Reactions Figure 7-9 The Calvin cycle fixes carbon from CO2 and produces the simple sugar G3P H2O CO2 ATP light reactions Calvin cycle NADPH ADP NADP sugar O2 C6H12O6 Carbon fixation combines three CO2 with three RuBP using the enzyme rubisco 3 CO2 6 3 PGA RuBP Calvin cycle 3 6 ATP 6 ADP ADP 6 NADPH 3 ATP 6 NADP 5 6 G3P Using the energy from ATP, the five remaining molecules of G3P are converted to three molecules of RuBP G3P Energy from ATP and NADPH is used to convert the six molecules of PGA to six molecules of G3P 1 G3P One molecule of G3P leaves the cycle 1 1 G3P Two molecules of G3P combine to form glucose and other molecules 1 G3P glucose Alternative pathways • Some plants use other pathways for carbon fixation – why? • When plant stomata are closed in hot environments to prevent water loss, oxygen builds up in the plant cells and RuBP combines with it, rather than CO2, in a wasteful process called photorespiration • This process prevents the Calvin cycle from synthesizing sugar, and plants may die under these circumstances C4 and CAM • When the Calvin cycle won’t work… • Flowering plants have evolved two different mechanisms to circumvent wasteful photorespiration • The C4 pathway • Crassulacean acid metabolism (CAM) Figure E7-1 The C4 pathway and the CAM pathway day night CO2 mesophyll cell PEP (3C) PEP carboxylase oxaloacetate (4C) pyruvate (3C) PEP (3C) PEP carboxylase malate (4C) pyruvate (3C) malate (4C) CO2 oxaloacetate (4C) mesophyll cell pyruvate (3C) rubisco Calvin cycle malate (4C) CO2 sugar rubisco bundle sheath cell C4 plants CO2 malic acid (4C) Calvin cycle sugar central vacuole CAM plants malate (4C) Last but not least • Do we have glucose yet? • In reactions that occur outside the Calvin cycle, what happens next? • What do plants do with all that glucose? Last but not least • Do we have glucose yet? • We’ve got a bunch of G3P • In reactions that occur outside the Calvin cycle, • two G3P (3-C) can be combined to form glucose (6-C) • What do plants do with all that glucose? • Convert to a disaccharide eg. ________(a storage molecule) or ______(a major component of plant cell walls) • Some glucose molecules are broken down in _______ ___________ to give the plant’s cells energy Compare photosynthesis with respiration • What process requires O2 as a reagent? • A – photosynthesis B – respiration C-both • Why? • What process requires CO2 as a reagent? • A – photosynthesis B – respiration C-both D-neither B – respiration C-both D-neither B – respiration C-both D-neither C-both D-neither • What process generates O2 ? • A – photosynthesis • CO2 ? • A – photosynthesis D-neither • What process generates ATP? • A – photosynthesis B – respiration • What process uses an electron transport chain? • A – photosynthesis B – respiration C-both D-neither A few more questions • What reactions MUST take place in the light? • • • • A – conversion of sunlight to ATP B – conversion of ATP to sugar C – both A and B D – none of the above • Do the dark reactions REQUIRE it to be dark? • A – yes B - no • Are plants the only photosynthesizers? • A – yes B - no • Do plants have mitochondria? • A – yes B - no Drawings! • Light reactions – what goes in, what comes out • Light reactions – trace the path of the electron • Dark reactions – what goes in, what comes out • Compare mitochondrial structure to chloroplast structure • Compare respiration to photosynthesis – focus on water and O2 • Compare respiration to photosynthesis – focus on CO2