Lecture 7: Capturing and Using Energy PDF

Lecture 7: Capturing and Using Energy  Today Photosynthesis – Sunlight and pigments – Chemical reactions – Photosynthetic pathways Aerobic respiration – Chemical reactions Anaerobic respiration (fermentation)  Energy Acquisition  Define...

Lecture 7: Capturing and Using Energy  Today Photosynthesis – Sunlight and pigments – Chemical reactions – Photosynthetic pathways Aerobic respiration – Chemical reactions Anaerobic respiration (fermentation)  Energy Acquisition  Define “food” according to what we’ve learned so far.  Energy Acquisition Autotrophs (producers) – Produce organic compounds from CO2 – Photoautotrophs – sunlight as energy source Plants Some bacteria Some protists  Energy Acquisition Heterotrophs (consumers) – Consume organic compounds originally made by autotrophs  Sunlight and Pigments Light contains energy – Photons – packets of light energy – Photons travel in waves according to their energy Higher energy, shorter wavelength Lower energy, longer wavelength  Sunlight and Pigments Pigments – light-absorbing molecules – Only absorb specific wavelengths – Reflected wavelengths seen as color  Is the entire spectrum of visible light used for photosynthesis?  Sunlight and Pigments Chlorophylls – Main pigments used by photoautotrophs – Chlorophyll a and chlorophyll b  Sunlight and Pigments Beta-carotene Carotenoids CH3 CH3 – Found in all photoautotrophs CH3  What color do carotenoids appear? CH3 CH3 CH3 CH3 CH3 CH3 CH3  Sunlight and Pigments Plants use a variety of pigments to absorb light  What is the advantage of using multiple pigments?  Photosynthesis Energy from sunlight used to Sunlight synthesize sugar from CO2 Oxygen Provides most biologically Carbon dioxide available energy on Earth Water  Photosynthesis Photosynthesis occurs in leaf mesophyll cells leaf’s upper surface photosynthetic cells central vacuole mesophyll chloroplast photosynthetic cell vein stoma (gap) in lower surface leaf cross section Stomata  Photosynthesis Inside the chloroplast: – Stroma – semifluid interior – Thylakoid membrane – folded, stacked inner membrane two outer membranes  How did chloroplasts evolve? inner thylakoid membrane system stroma  Photosynthesis Inside the chloroplast: – Photosystems – clusters of pigments and proteins embedded in thylakoid membrane – Capture light energy light harvesting electron complex transfer chain PHOTOSYSTEM II PHOTOSYSTEM I thylakoid thylakoid membrane compartment  Chemical Reactions of Photosynthesis Two stages of photosynthesis: sunlight H2O CO2 energy (water) (carbon dioxide) ATP 1. light- 2. light- Capturing dependent ADP + Pi independent Making reactions sunlight reactions sugar NADPH (photo) NADPH+ (synthesis) glucose O2 H2O (metabolic water)  Chemical Reactions of Photosynthesis Two stages of photosynthesis: 1. Light-dependent reactions – light energy captured and stored in ATP & NADPH – Occur at thylakoid membrane – Electron transfer chains 2. Light-independent reactions – ATP & NADPH used to convert CO2 into sugar – Occur in stroma – Calvin-Benson cycle  Light-Dependent Reactions Process: – Pigments in photosystem absorb light energy – Light energy causes photosystem to release electrons – Electrons enter electron transfer chains on membrane – Energy from electron transfer used to produce ATP & NADPH  Light-Dependent Reactions Process: light 8 1 light energy electron 5 energy electron transfer 4 transfer 3 chain 6 chain ATP synthase ADP, photosystem phosphate thylakoid 2 compartment H O 2 7 stroma O2  Light-Dependent Reactions ATP formation by electron transfer phosphorylation: – Energy from ETC used to actively transport H+ into thylakoid compartment – H+ concentration gradient forms – H+ flows down gradient through ATP synthase – Flow of H+ drives formation of ATP  Light-Independent Reactions Calvin-Benson Cycle: – “Fixes” inorganic CO2 carbon (from CO2) into glucose PGA RuBP Calvin ATP – Uses ATP and ATP Cycle NADPH NADPH – Catalyzed by rubisco sugars  Light-Independent Reactions Calvin-Benson Cycle: 6CO2 1 2 Intermediate Rubisco adds CO2 to RuBP compounds (ribulose ATP (PGA and PGAL) biphosphate) 6 RuBP 12 PGA form 12 6 ADP Calvin-Benson 12 ADP + ATP cycle 12 Pi 12 NADPH Using ATP, RuBP 4 3 Using ATP and is regenerated 4 Pi NADPH, PGAL is 12 NADP+ converted into 10 PGAL 12 PGAL glucose 1 Pi 1 glucose-6-1-phosphate  Photosynthesis Summary sunlight Light- Dependent 12H2O 6O2 Reactions ADP + Pi ATP NADPH NADP+ 6CO2 Calvin- 6 RuBP Benson 12 PGAL cycle Light- 6H2O Independent Reactions phosphorylated glucose end products (e.g., sucrose, starch, cellulose)  Photosynthetic Pathways C3 photosynthesis – CO2 captured by rubisco, fixed into 3-C molecule – Rubisco also catalyzes photorespiration RuBP PGA (consumes O2 and Calvin- Benson releases CO2) cycle – Photorespiration is a net energy loss sugar  Photosynthetic Pathways C4 photosynthesis – CO2 fixed first in mesophyll cell mesophyll cells C4 oxaloacetate cycle – Moved to interior bundle bundle sheath cells CO2 sheath for Calvin Cycle RuBP PGA cell Calvin- Benson – Reduces cycle photorespiration sugar  Photosynthetic Pathways CAM photosynthesis CO2 uptake at night only – CO2 taken up only at night, stored until daytime runs C4 at  Where is it stored? cycle night – Calvin Cycle proceeds Calvin- during daytime Benson runs during cycle day  Benefit? sugar Photosynthetic Pathways Spatial separation C3 default C4 reduces photorespiration CAM reduces evaporation Temporal separation Photosynthetic Pathways C3: 85% of global plant species, tropical – temperate CAM: 8%, dry deserts C4: 3%, hot/dry grasslands  Cellular Respiration Cellular respiration – metabolic reactions that convert stored energy in food to usable energy  What is “food”? What is “usable energy”? – Aerobic respiration – occurs in presence of oxygen – Anaerobic respiration – occurs without oxygen  Aerobic Respiration Process of aerobic respiration: 1. Glycolysis breaks down glucose 2. Krebs Cycle produces coenzymes 3. Electron transfer chain powers ATP formation C6H12O6 + 6O2 → 6CO2 + 6H2O + 36 ATP  Aerobic Respiration cytoplasm glucose 2 ATP ATP GLYCOLYSIS energy input to start reactions e- + H+ (2 ATP net) 2 pyruvate 2 NADH mitochondrion e- + H+ 2 CO2 2 NADH e- + H+ 8 NADH 4 CO2 e- + H+ Krebs 2 ATP 2 FADH2 Cycle e- ELECTRON TRANSPORT 32 ATP PHOSPHORYLATION H+ water e- + oxygen TYPICAL ENERGY YIELD: 36 ATP  Aerobic Respiration 1. Glycolysis – Occurs in cytoplasm – Glucose converted to two pyruvates  How many carbons in pyruvate? – Produces 2 ATP plus 2 NADH  Aerobic Respiration 2. Acetyl-CoA formation and Krebs Cycle – Occurs in mitochondria – Pyruvate broken down into acetyl-CoA, then CO2 – Produces 2 ATP plus 8 NADH and 2 FADH2 inner outer mitochondrial mitochondrial membrane membrane inner outer compartment compartment  Aerobic Respiration 2. Acetyl-CoA formation and Krebs Cycle Acetyl-CoA pyruvate Formation coenzyme A NAD+ (CO2) NADH CoA acetyl-CoA Krebs Cycle CoA oxaloacetate citrate NAD+ (CO2) NADH NAD+ NADH FADH2 NAD+ (CO2) FAD NADH ATP ADP + phosphate group  Aerobic Respiration 3. Electron transfer chain – Occurs at inner mitochondrial membrane – NADH and FADH2 deliver electrons – Electron transfer sets up H+ concentration gradient – Flow of H+ down gradient drives ATP formation  Aerobic Respiration 3. Electron transfer chain ATP synthase  Summary of Aerobic Respiration glucose ATP 2 PGAL ATP 2 NADH Glycolysis: 2 pyruvate 2 ATP glycolysis + 2 FADH2 Krebs cycle: 2 CO2 e– 2 ATP 2 acetyl-CoA 2 NADH H+ + H+ 2 ATP Krebs 6 NADH H+ Electron transfer: ATP Cycle 2 FADH2 ATP H+ ~32 ATP 4 CO2 34 ATP H+ H+ ADP electron + Pi transfer H+ H+ phosphorylation 36 ATP H+  Anaerobic Respiration Fermentation – anaerobic metabolism of carbohydrates Produces much less ATP than aerobic pathways Two types: – Alcoholic fermentation – Lactate fermentation  Anaerobic Respiration Steps of fermentation: 1. Glycolysis – produces 2 ATP 2. Processes that regenerate coenzyme NAD+ ATP formed by glycolysis only Occurs in cytoplasm only Cyclic pathways  Anaerobic Respiration Alcoholic glycolysis fermentation: ATP C6H12O6 2 energy input 2 ADP 2 NAD+ – Converts pyruvate 2 NADH 4 ATP to ethanol energy output 2 pyruvate 2 ATP net – Ex: baking, ethanol 2 H2O formation wine & beer 2 CO2 production 2 acetaldehyde electrons, hydrogen from NADH 2 ethanol  Anaerobic Respiration Lactate fermentation: glycolysis C6H12O6 2 ATP – Converts pyruvate energy input 2 ADP 2 NAD+ to lactate 2 NADH 4 ATP energy output 2 pyruvate – Ex: cheese, yogurt, 2 ATP net some skeletal lactate muscles formation electrons, hydrogen from NADH 2 lactate  Food and Energy Glucose is not the only molecule used to make ATP Carbohydrates, fats, and proteins can all be used for cellular respiration – May enter glycolysis – May enter acetyl-CoA formation – May enter Krebs Cycle Food and Energy  Study Questions What is an autotroph? What is a heterotroph? What is the energy source that drives photosynthesis? What are the “goals” of the light-dependent and light-independent stages (Calvin Cycle) of photosynthesis? What products does each produce? Where specifically does each occur? Describe in detail the process of the light-dependent reactions. Explain how electron transfer chains and ATP synthase work to produce ATP in both photosynthesis and aerobic respiration. What is photorespiration, and under what conditions does it occur at high rates? What are C3, C4, and CAM? What sort of plants do each? Describe the steps involved in aerobic respiration. What are the “goals” of each step? Where does each step occur? Compare and contrast aerobic and anaerobic respiration.