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Biochemical Pathways: Photosynthesis Chapter 7 2- Photosynthesis Photosynthesis is performed by Autotrophic Organisms – Autotrophs produce their own food – chemoautotrophs, photoautotrophs Photosynthetic autotrophs capture energy from the sun to produce their own food • 7- “Auto” = self; “Trophic” = feeding Plants, algae and some bacteria are photosynthetic Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Photosynthesis Photoautotrophs: photosynthetic organisms that can produce their own ‘food’ - these organisms fix the energy of sunlight into carbohydrate form they then use the carbohydrates they produce for cellular respirationHeterotrophs: organisms that require an alternative food source - these organisms consume photoautotrophs along with the - 7- carbohydrates they produce they then use the carbohydrates they consume for cellular respiration Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Photosynthesis The process by which photosynthetic organisms produce their own high energy organic molecules – Photosynthesis captures energy from the sun and fixes it into the chemical form – 7- Primarily carbohydrates Carbon Fixation Carbon Fixation: Photosynthesis collects the energy of sunlight and captures it in a chemical form Photosynthesis uses CO2 to build carbohydrates:(C6H12O6) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Photosynthesis and Life Most living things depend on the sun for energy – Photosynthetic organisms serve as a food and energy source for the majority of life on on earth – 7- Photosynthetic organisms directly or indirectly provide energy for the majority of the life on earth A few exceptions include chemoautotrophs: autotrophic organisms that utilize energy from other sources, live independently from the sun Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Photosynthesis and Life Energy Fixation – Oxygenic photosynthesis maintains O2 in the atmosphere – 7- vital for aerobic respiration Removes CO2 from the atmosphere – makes the sun’s energy available to other organisms reduces green house gases H2O production Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Overview of Photosynthesis: The Energy Cellular Respiration: – CO2 + H2O + Energy (ATP) Photosynthesis: – 7- Carbohydrate + O2 Energy (Sun) + CO2 + H2O Carbohydrate + O2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Overview of Photosynthesis: The Chemistry 6CO2 + 12H2O carbon dioxide water C6H12O6 + 6H2O + 6O2 glucose water oxygen Reactants: 6CO2 + 12H2O Products: C6H12O6 + 6H2O + 6O2 Photosynthesis vs. Cellular Respiration: 6CO2 + 12H2O C6H12O6 + 6H2O + 6O2 C6H12O6 + 6O2 6CO2 + 12H2O + Energy 7- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Overview of Photosynthesis Photosynthesis occurs in the Chloroplasts Chloroplasts contain a pigment that captures the energy in light – Chlorophyll is most common pigment of chloroplasts – – 7- A pigment is a molecule that absorbs light energy and transfers it to electrons There are several types of chlorophyl There are also many accessory pigments Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The Chloroplast Similar in structure to a mitochondria – Inner membrane is folded into sacs known as thylakoids – Chlorophyll is contained thylakoid sacs A stack of thylakoid is called a granum (pl. grana) – 7- Outer and inner membrane Grana are suspended in a fluid-filled space called the stroma Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 7_05 Figure 7_02 Fig. 8.1-2 The Relationship between Photosynthesis and Cellular Respiration • Photoautotrophs • Chloroplasts • grana and thylakoids • ETC • NADP+ reduced to NADPH • ATP synthase, ATP production • Calvin Cycle Heterotrophs •Mitochondria -mitochondrial membrane, cisternae •Krebs Cycle -Carbohydrates to CO2 oxidized •ETC -NAD+ reduced to NADH -ATP synthase, ATP 14 production Overview of Photosynthesis Three events of photosynthesis 1. Light-capturing events – The pigment chlorophyll absorbs certain wavelengths of light to excite electrons 2. Light-dependent reactions – Excited electrons enter an ETC to make ATP and NADPH. NADPH has a the same function and similar structure to NADH - NADP+ is reduced to NADPH 3. Light-independent reactions – 7- ATP and NADPH from the light reactions are used to reduce carbon dioxide to make glucose. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Light Energy travels as waves through a medium Different types of energy have different wavelengths – The spectrum of visible light energy ranges from 350 - 790 nm – – 7- Microwaves, radio waves, x rays, gamma rays, visible light – Different wavelengths in the visible spectrum are seen by our eyes as different colors ROY G BI(V) White light is a combination of all the different wavelengths of visible Copyright light © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 7_04 Light When light strikes any object some light is absorbed by pigments, the rest of the light is reflected off of the object Pigments are molecules that absorb light: – – 7- Each Pigment only absorbs certain wavelengths of light The wavelengths that are not absorb are reflected Our eyes see objects by receiving the reflected light – We only see the unabsorbed light Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Text art 7_01 What color is the tomato? The tomato is really every color except for red Light Light is measured in photons – The energy in a photon is related to its wavelength – – 7- a photon is the unit of light shorter wavelength = higher energy longer wavelength = lower energy When a photon hits a pigment molecule, electrons are excited – the electrons jump up to a higher energy level Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1. Light-Capturing Events In photosynthesis, the wavelengths that are absorbed by pigments can be used for energy Chlorophyll is the main photosynthetic pigment – – – 7- Two forms; a and b Absorb light in the blue and red portions of the spectrum Reflect green wavelengths Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Other Types of Pigments Accessory pigments carotenoids – – Absorb blue and green wavelengths Reflect orange and yellow Also found in leaves but usually masked by chlorophyll – 7- Used in addition to chlorophyll to absorb more of the spectrum In the autumn, when chlorophyll disintegrates, accessory pigments show through (fall colors). Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Other Types of Pigments Chlorophyll + accessory pigments – 7- Organized into photosystems that harvest the energy from many wavelengths of light Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1. Light-Capturing Events The light-capturing events take place in Photosystems – cell structures in the thylakoid membranes Photosystems are composed of: A.Antenna Complexes networks of chlorophyll and accessory pigments B.Reaction Center 7- composed of specialized chlorophyll molecule that passes its excited electrons to an electron acceptor. There are two photosystems, I and II. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 25 A. Antenna Complexes Networks of chlorophyll and accessory pigments Able to capture many available wavelengths of light Passes excited electrons on to the Reaction Center 7- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. B. Reaction Center Specialized chlorophyll molecule collects energy from the antenna complex Energy excites electrons, excited electrons passed to an electron acceptor – – 7- PS II passes electrons to the electron transport chain to make ATP PS I passes electrons to NADP+ to make NADPH’s Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 28 Two Photosystems: The Z Scheme Photosystem II (PSII) Aka P680 Occurs first in the light-dependent reactions Donates its excited electrons to an electron transport chain Splits water to replace the electrons it donated - 7- 2H2O O2 + 4H+ + 4e-’s O2 is released Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Photosystems: The Z Scheme Aka P700 Occurs second in the light-dependent reactions Donates its excited electrons to reduce NADP+ to NADPH: NADP+ + eNADPH – 7- Photosystem I (PSI) NADPH released into the stroma to be used later in the light-independent reactions Accepts electrons from the electron transport chain between PSII and PSI to replace the electrons it donated Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2. Light-dependent Reactions: The Electron Transport Chain Occurs between PSII and PSI – Electrons are passed through an electron transport chain (ETC) 7- The energy is used to pump protons from the stroma into the thylakoid space Creates a proton concentration gradient Protons diffuse through ATP synthase ATP synthase makes ATP that is released into the stroma Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 7_07 2. Light-Dependent Reactions: The excited electrons from chlorophyll are passed through an electron transport chain to produce ATP – Water is the source of electrons – water is oxidized to produce oxygen in PSII Electrons are carried by NADPH from PSI – 7- Similar process as cellular respiration to be used in light-independent reactions Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 7_07 3. Light-Independent Reactions The Calvin Cycle – – incorporates CO2 into organic molecules – occurs in the stroma – uses ATP from light-dependent reactions – 7- biochemical pathway that allows for carbon fixation NADPH from light-dependent reaction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3. Light-Independent Reactions To build carbohydrates, cells need: 1. Carbon and oxygen atoms: from CO2 2. Hydrogen atoms: provided by NADPH from photosystem I 3. Energy: provided by ATP from ETC of light-dependent reactions 7- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Carbon Fixation and Sugar Formation Reactants 1.CO2 - from the atmosphere 2.ATP and NADPH - from the light-independent reactions 3.Ribulose - a 5-carbon sugar - recycled throughout the cycle 7- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3. Light-Independent Reactions CO2 is captured from the atmosphere – 7- RuBisCO is an enzyme in the stroma that captures CO2 CO2 enters and O2 leaves the leaf through the stoma Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3. Light-independent Reactions CO2 + Ribulose (5-C’s) Carbon Fixation 6-C intermediate Sugar Formation: Reduced by NADPH 2 Glyceraldehyde-3-phosphates (G-3-P) G-3-P is used to make sugars, proteins or fats 7- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 7_06 1. Carbon Fixation Carbon from the atmosphere is “fixed” into carbohydrates – CO2 is combined with ribulose, accomplished with an enzyme (RuBisCO) Forms a 6-carbon intermediate molecule Immediately broken down into two 3-carbon molecules: 2 PGA’s 7- CO2 + Ribulose 2PGA 1 carbon 3 carbons each 5 carbons Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2. Sugar Formation PGA molecules are phosphorylated by ATP and reduced by NADPH 7- PGA ATP, NADPH G-3-P Final product: 2 Glyceraldehyde-3-phosphates (G-3P) are formed G-3-P can be used to make glucose, fructose, starches, cellulose, etc. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3. Regeneration of Ribulose 7- Recall: 2 Glyceraldehyde-3-phosphates (G-3-P)’s are made during the Carbon Fixation and Sugar Formation Steps One G-3-P is transported from the chloroplast and used to make glucose, fructose, starches, cellulose, etc. The other G-3-P is returned to the Calvin cycle and used to make another Ribulose G-3-P Regeneration Steps of Calvin Cycle Ribulose Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The Calvin Cycle 7- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glyceraldehyde-3-phosphate: The Product of Photosynthesis Glyceraldehyde-3phosphate can be used for many things: – – – – – 7- – Used to make glucose Used to recycle ribulose for the Calvin cycle Used to make the sugars needed to build ATP, DNA and RNA Can be converted into lipids Can be converted into amino acids to make proteins Can beCopyright broken down in © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. glycolysis Other Aspects of Plant Metabolism Plant cells use the organic G-3-P molecules produced in photosynthesis: – – Production of fats, proteins and other carbohydrates Production of toxins for their protection – Production of vitamins 7- Many of these are useful medicines. Some can be used as natural insecticides. Molecules that we cannot make, but that we need Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The Relationship between Photosynthesis and Cellular Respiration • Photoautotrophs • Chloroplasts • grana and thylakoids • ETC • NADP+ reduced to NADPH • ATP synthase, ATP production • Calvin Cycle Heterotrophs •Mitochondria -mitochondrial membrane, cisternae •Krebs Cycle -Carbohydrates to CO2 oxidized •ETC -NAD+ reduced to NADH -ATP synthase, ATP 47 production Interrelationships Between Autotrophs and Heterotrophs Autotrophs use the energy in light to make food – Autuotrophs use the food they make in cellular respiration Heterotrophs eat the autotrophs – – Use the food from the autotrophs to fuel cellular respiration Use the excess oxygen given off by autotrophs for cellular respiration The circle of life: – – 7- Plants use the carbohydrates they produce for cellular respiration Plants use the oxygen they produce for cellular respiration Animals get sugar, oxygen, amino acids, fats and vitamins from plants Plants get carbon dioxide, water and nitrogen from animals Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The Relationship between Photosynthesis and Cellular Respiration 7- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. All 7- Organisms Respire Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
