Cellular Energy: hotosythesis Cellular respiration and photosynthesis are chemical reactions that provide kinetic and potential energy for cells Sunlight energy hotosynthesis in chloroplasts Glucose + + Cellular respiration in mitochondria O 2 Is photosynthesis exergonic or endergonic? Endergonic it absorbs energy from the environment and stores it as potential energy in sugar Is cellular respiration exergonic or endergonic? Exergonic it breaks chemical bonds to release potential energy into kinetic energy (for cellular work) Heat energy hotosynthesis Autotrophs make their own food and do not need to consume other organisms or organic molecules. hotoautotrophs - plants, algae, certain protists, and prokaryotes that make food molecules from and using the energy of light (in contrast to chemoautotrophs). These are the ultimate producers of food that are consumed (eventually). This energy conversion process is called photosynthesis and takes place in specialized organelles called. chloroplasts 1
Location and structure of chloroplasts Where does photosynthesis occur? A chloroplast contains: Stroma: fluid that fills the chloroplast. Granum, which are stacks of thylakoids. Enzymes needed to carry out photosynthesis. Chloroplast Stroma Inner and outer membranes Granum Transmission electron microscopy 9,750 Intermembrane space Where does photosynthesis occur? The thylakoids contain chlorophyll. Chlorophyll is the green pigment molecule that plays a major role in the capture of light energy for photosynthesis. Chloroplast Stroma Inner and outer membranes Granum Transmission electron microscopy 9,750 Intermembrane space 2
hotosynthesis is the set of chemical redox reactions that plants use to make food in the form of glucose. energy 6 + 6 C 6H 12O 6 + 6 O 2 Carbon dioxide Water Glucose Oxygen gas hotosynthesis The water is split and its oxygen atom is released as O 2 and its hydrogen atoms go into the sugar molecule. hotosynthesis is the set of chemical redox reactions that plants use to make food in the form of glucose. Energy energy 6 + 6 C 6H 12O 6 + 6 O 2 Carbon dioxide Water Glucose Oxygen gas hotosynthesis Compare photosynthesis with cellular respiration: Loss of hydrogen atoms (oxidation) C 6 H 12 O 6 + 6 O 2 Glucose Gain of hydrogen atoms (reduction) 6 + 6 + Energy () hotosynthesis is a redox reaction The movement of electrons (e -s ) from one molecule to another is an oxidation-reduction or redox reaction. In organic reactions the e -s are often transferred with hydrogen atoms. Oxidation occurs when a substance looses e -s. Reduction occurs when a substance gains e -s. Both an oxidation and a reduction occur in a redox reaction. 3
hotosynthesis occurs in two stages Stage 1: reactions Stage 2: Calvin Cycle hotosynthesis occurs in two stages Stage 1: reactions Occurs in the thylakoids of chloroplasts. These reactions convert light energy captured by chlorophyll into chemical energy (in the form of, which will be converted to glucose) Water is split to produce O 2 the H+ and e- s are picked up by the electron carrier... What molecule carries electrons? NAD+ (and FAD+) in cellular respiration NAD+ is the carrier in photosynthesis hotosynthesis Chloroplast NAD + AD LIGHT REACTIONS (in thylakoids) 4
hotosynthesis Chloroplast NAD + AD LIGHT REACTIONS (in thylakoids) NADH O 2 hotosynthesis occurs in two stages Stage 1: reactions Occurs in the thylakoids of chloroplasts. These reactions convert light energy captured by chlorophyll into chemical energy (in the form of, which will be converted to glucose) Water is split to produce O 2 the H+ and e- s are picked up by the electron carrier NAD. Stage 2: Calvin cycle Occurs in the stroma of the chloroplasts. series of chemical reactions use the and NADH produced during the light reactions to produce energy-rich glucose from. - The process of converting inorganic to organic compounds is called carbon fixation. hotosynthesis Chloroplast LIGHT REACTIONS (in thylakoids) NAD + AD CALVIN CYCLE (in stroma) NADH O 2 Sugar 5
Stage 1: reactions visible radiation drives the light cycle Sunlight is a type of energy referred to as electromagnetic energy (radiation). Shorter wavelengths have more energy than longer wavelengths Stage 1: Reactions Chlorophyll captures photons is absorbed Higher energy, unstable electron Low energy, stable electron Chlorophyll within thylakoid The absorbed light excites electrons in chlorophyll. Chlorophyll transfers those electrons to molecules Stage 1: Reactions hotosystems Chlorophyll molecules are organized with other proteins and pigments, this complex is referred to as a photosystem. Chlorophyll alone will reflect energy it needs other molecules to accept the excited electrons 6
Stage 1: Reactions hoton hotosystem -harvesting complexes Reaction center complex rimary electron membrane e igments: Transfer igment Chlorophyll b of energy Chlorophyll air a molecules of molecules (yellowish) are Chlorophyll specially positioned a molecules to donate Carotenoids electrons to the reaction center (orange/red) Stage 1: Reactions hotosystems Capture Solar ower There are two different photocenters (I and II) Each type of photosystem has a characteristic reaction center hotosystem I accepts absorbs light best at 700 nm and photosystem II absorbs light at 680 nm Stage 1: Reactions hoton hotosystem -harvesting complexes Reaction hotosystem I and II have center different complex primary e- s, that rimary absorb electron different wave lengths of light membrane e igments: Transfer igment Chlorophyll b of energy Chlorophyll air a molecules of molecules Carotenoids are Chlorophyll specially positioned a molecules to donate electrons to the reaction center 7
Stage 1: reactions visible radiation drives the light cycle H I: 700, H II: 680 We see color when the wave lengths of light that are not absorbed by an object are reflected back into our eyes. For example, when you look something black, it is actually absorbing all of the visible light and reflecting nothing back when we see white the object is reflecting the entire spectrum back. Knowing this, and knowing what light waves are absorbed by photosystems I and II, explain why leaves appear green during the summer? Stage 1: reactions visible radiation drives the light cycle H I: 700, H II: 680 Shorter wavelengths have more energy than longer wavelengths but water absorbs shorter wave lengths of light (this is why red things appear black in deep water short wave lengths are filtered out by the water and they cannot reflect off of objects and back into our eyes to permit us to see them). How does this explain why aquatic plants only live in the top 10-15 m of water? What light spectrum would you expect aquatic plants to use and what color would you expect aquatic plants to be when brought to the surface? Stage 1: Reactions hotosystems Capture Solar ower There are two different photocenters (I and II) Each type of photosystem has a characteristic reaction center hotosystem I accepts absorbs light best at 700 nm and photosystem II absorbs light at 680 nm hotosystems I and II are connected by an electron transport chain These systems work together to generate and NADH 8
Stage 1: Reactions hotosystems and electron transport chain Stroma hoton hotosystem II hoton NAD + + H + hotosystem I NADH membrane space 1 2 O 2 + 2 H + What do electron transport chains do? Electron transport chain rovides energy for synthesis of by chemiosmosis Stage 1: Reactions hotosystem II Stroma hoton hotosystem II Electron transport chain NAD hoton + H rovides energy for harvesting complex + + synthesis of hotosystem I by chemiosmosis absorbs a photon of light NADH membrane rimary e e 680 rimary An electron form p680 is excited and is captured by the primary electron 700 space 1 2 O 2 + 2 H + H 2 0 is split providing a source of electrons and releasing O2 Stage 1: Reactions Electron transport Stroma hoton membrane space hotosystem II rimary 680 1 2 O 2 + 2 H + Electron transport chainhoton e e The photoexcited NAD + H + NADH electron passes + from hotosystem I photosystem II to I via an electron transport rimary chain This falling electron 700 provided energy for the synthesis of. 9
Stroma hoton hotosystem II Electron transport chain hoton NAD + + H + hotosystem I NADH membrane rimary e e 680 rimary 700 space 1 2 O 2 + 2 H + A light-energy excited e- from 700 is passed to the primary electron. This excited electron is passed through a short electron chain and NDA+ is reduced to NADH. An electron from the electron transport chain replaces the lost p700 electron. Stage 1: Reactions e e e e e e NADH Mill makes hoton e hoton hotosystem II hotosystem I How is formed???? 10
hotophosphorylation is synthesized by chemiosmosis is generated because the electron transport chain produces a concentration gradient of hydrogen ions across a membrane NADH and then feed into the Calvin cycle Remember: chemiosmosis powers synthesis in the light reactions Stroma (low H + concentration) H + NAD + + H + NADH H + AD + H + H + 1 O 2 2 + 2 H + H + H+ hotosystem II Electron transport space chain (high H + concentration) H+ H + H+ H + hotosystem I H + H + H + H + synthase hotosynthesis occurs in two stages Stage 1: reactions Occurs in the thylakoids of chloroplasts. These reactions convert light energy captured by chlorophyll into chemical energy (in the form of, which will be converted to glucose) Water is split to produce O 2 the H+ and e- s are picked up by the electron carrier NAD. Stage 2: Calvin cycle Occurs in the stroma of the chloroplasts. series of chemical reactions use the and NADH produced during the light reactions to produce energy-rich glucose from. 11
Calvin cycle is a set of chemical reactions Input NADH The Calvin cycle functions like a sugar factory within the chloroplast. CALVIN CYCLE and NADH are from the light cycle. is from the environment. Output: G3 G3 = glyceraldehyde-3-phosphate is used to make glucose and other organic molecules. Input: 3 The chemical reactions of the Calvin cycle Rubisco 1 3 RuB 6 3-GA Rubisco is an enzyme. CALVIN CYCLE Calvin cycle is a series of chemical reactions driven by enzymes! 12
Input: 3 The chemical reactions of the Calvin cycle Rubisco 1 3 RuB 6 3-GA 6 CALVIN CYCLE 2 6 AD + 6 NADH 6 NAD + 6 G3 Input: 3 Rubisco 1 3 RuB 6 3-GA 6 CALVIN CYCLE 2 6 AD + 6 NADH 6 NAD + 5 G3 3 6 G3 Output: 1 G3 Glucose and other compounds Input: 3 Rubisco 1 3 RuB 6 3-GA 3 AD 6 3 4 CALVIN CYCLE 2 6 AD + 6 NADH 6 NAD + 5 G3 3 6 G3 Output: 1 G3 Glucose and other compounds 13
hotosynthesis Chloroplast LIGHT REACTIONS (in thylakoids) NAD + AD CALVIN CYCLE (in stroma) NADH O 2 Sugar 14