_Photosynthesis_Jan_24-1.pptxbfgdfjignjg

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1. Photosynthesis Premed/ Prepha

2. ATP Remember… ATP is cellular energy Energy from the chemical bonds of ATP is released when the bond between the 2 nd and 3 rd phosphate groups is broken. It then becomes adenosine DIphosphate – ADP ATP is then recharged! It uses energy to gain an extra P and become ATP again

3. Metabolism Anabolism : metabolic reactions that build molecules [endergonic reaction] Catabolism : metabolic reactions that break down molecules [exergonic reaction] Life is sustained by inputs of energy, however not all forms of energy can sustain life. The sun is abundant, but cannot directly power protein synthesis or energy-requiring reactions, it must first be converted to chemical bond energy

4. Photosynthesis Photosynthesis is the process by which plants, algae, and some bacteria convert energy from the sun into chemical energy that can be used to fuel their growth and reproduction. The process is essential for life on Earth, as it forms the basis of the food chain and produces the oxygen that is necessary for the survival of many living organisms Photosynthesis occurs in the chloroplasts of plant cells, which are organelles that contain chlorophyll, a green pigment that absorbs light energy. The process can be broken down into two main stages: the light-dependent reactions and the light-independent reactions (also known as the Calvin cycle).

5. Stages The light-dependent reactions take place in the thylakoid membrane of the chloroplasts and involve the absorption of light energy by chlorophyll. This energy is used to generate ATP (adenosine triphosphate), which is a source of chemical energy, and NADPH (nicotinamide adenine dinucleotide phosphate ), which is a source of reducing power. The light-independent reactions take place in the stroma of the chloroplasts and involve the use of the ATP and NADPH generated in the light-dependent reactions to convert carbon dioxide (CO2) into organic compounds, such as glucose. This process is also known as carbon fixation.

6. Photosynthesis Photosynthesis : Metabolic pathway that uses light energy to turn carbon dioxide (CO2) and water (H2O) into carbohydrates (sugar) Also creates OXYGEN! The process is cyclical, the products from one reaction are the reactants for the next reaction

7. Photosynthesis Photosynthesis has 2 parts Light-dependent : converts light energy into chemical energy; produces oxygen and ATP to be used in light-independent reaction Light-independent : does not require light energy, uses CO2 and H2O to build sugars; powered by ATP, also called the CALVIN CYCLE

8. Chloroplasts Photosynthesis occurs in the chloroplast The chloroplast is a plastid that carries out photosynthesis Plastids are double membrane organelles that contain pigment Chloroplasts resemble the photosynthetic bacteria they evolved from, so photosynthesis in eukaryotic cells is similar to bacterial photosynthesis

9. Chloroplasts Thylakoid membrane : Highly folded into stacks of interconnected thylakoids [Light-dependent reactions] Folds in this membrane form disks called thylakoids The membrane encloses a single, continuous internal space Stroma : Cytoplasm-like fluid inside the chloroplast [Light-independent reactions] thylakoid membrane, ribosomes, and chloroplast’s DNA are suspended in the stroma

10. Photosynthesis Pigment : organic molecule that selectively absorbs certain wavelengths of light If a wavelength is not absorbed, it is reflected, and that gives the pigment its color Chlorophyll a is the most common pigment in plants It absorbs violet, red, and orange light, but reflects green!

11. Phase 1: Light Reaction 1. Light hits a leaf, causing an electron in chlorophyll to enter an excited state (higher energy level) within the chloroplast’s thylakoid membrane. 2. The excited electrons leaves the chlorophyll and an enzyme splits a water molecule to replace the electron lost by the chlorophyll. Oxygen gas is formed and exits through the membrane and into the atmosphere. H + ions accumulate inside the thylakoid space. LIGHT H 2 O H + O 2 Ferredoxin

12. 3. The released electron goes through electron transport chain . The electron is bounced from between proteins in the thylakoid membrane. Note: Energy lost along electron transport chain 4. The electron is eventually passed to another chlorophyll molecule and then on to the final electron acceptor (ferredoxin NADP + reductase) where the electron transport chain ends. 5. Ferredoxin NADP + reductase then gives the electron to an electron carrier NADP which turns it into NADPH. NADPH carriers the electron to the next phase. H + O 2 H + H + Ferredoxin NADP NADPH

13. 6. As more copies of steps 1 through 5 occur, more and more H + ions from step 2 begin to build up in the thylakoid space. H + ions begin to pass from an area of higher concentration (thylakoid space) to an area of lower concentration (stroma) through an enzyme called ATP synthase. This process called, chemiosmosis, creates ATP. H + H + H + Ferredoxin ADP ATP H + H + H + H + H + H +

14. Phase 1: Light Reaction Summary Lost energy used to recharge ATP from ADP NADPH produced from e- transport chain Stores energy until transfer to stroma Plays important role in light-independent reaction (LIR) Total byproducts: ATP (Used in LIR), NADPH (Used in LIR), O 2 (Exits plant)