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Sources of energy

Sources of energy. Cells derive energy from: Sunlight The oxidation of organic molecules The oxidation of inorganic molecules. Photosynthesis The trapping and conversion of light energy into chemical energy Light energy  ATP + NADH /NADPH. Photosynthesis

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Sources of energy

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  1. Sources of energy Cells derive energy from: Sunlight The oxidation of organic molecules The oxidation of inorganic molecules

  2. Photosynthesis The trapping and conversion of light energy into chemical energy Light energy  ATP + NADH /NADPH

  3. Photosynthesis The trapping and conversion of light energy into chemical energy The reduction and incorporation of CO2 into organic material

  4. Roles of photosynthesis Provides organisms with the energy to synthesize organic material organisms serve as the base of most food chains Replenishes the planet’s supply of O2

  5. Photosynthesis Almost all energy on Earth is ultimately derived from solar energy More than half of all photosynthesis is carried out by microorganisms

  6. Photosynthesis Light reaction Light energy converted to chemical energy Dark reaction Chemical energy used to reduce and incorporate CO2 into organic molecules

  7. Light absorbing pigments Absorb energy of light and transfers energy via excited electrons

  8. Chlorophylls Most important photosynthetic pigments Planar rings composed of 4 pyrole rings with a central magnesium atom Hydrophobic tail aids in attachment to membranes

  9. Chlorophylls a and b Common in eukaryotes Absorb light at 650 + 430 nm Transmit green light  green color

  10. Chlorophylls a and b Common in eukaryotes Absorb light at 650 + 430 nm Transmit green light  green color

  11. Bacteriochlorophylls Found in green and purple photosynthetic bacteria Absorb light at longer wavelengths

  12. Bacteriochlorophylls

  13. Accessory pigments Carotenoids - long molecules (usually yellow) Phycobiliproteins - protein attached to a tetrapyrole ring Algae Diatoms + dinoflagellates Red algae and cyanobacteria

  14. Accessory pigments Carotenoids Phycobiliproteins Absorb energy from wavelengths that chlorophylls cannot Transfer energy to chlorophylls

  15. Antennas Arrays composed of chlorophylls and accessory pigments Large surface area to trap photons Light energy transferred to reaction-center chlorophyll

  16. Photosystems I and II Eukaryotes and many prokaryotes possess 2 photosystems I - absorbs light greater than 680 nm II absorbs light lower than 680 nm

  17. Photosystem I P700 -reaction-center chlorophyll Absorbed energy transferred to P700 Donates excited electron to an acceptor (Chlorophyll a or FeS) Electron transferred to ferredoxin then travels 1 of 2 pathways

  18. Cyclic pathway Electron moves through a series of carriers Travels back to P700 PMF formed and used to generate ATP  cyclic photophosphorylation

  19. Noncyclic pathway Ferredoxin reduces NADP+ to NADPH + H+ Photosystem II donates electrons to P700

  20. Photosystem II P680 absorbs light energy Electron moves to pheophytin a Electron moves to Q then to P700

  21. Photosystem II P680 obtains electron from H2O  O2 Synthesis of ATP is by noncyclic photophosphorylation

  22. Photosynthetic electron transport chain Takes place in a membrane Structure referred to as a thylakoid

  23. Photosynthetic electron transport chain In plants takes place in the thylakoid membrane of chloroplasts

  24. Green and purple photosynthetic bacteria Do not use water as electron donor Do not produce O2 Photosynthesis that produces O2 = oxygenic Photosynthesis that does not produce O2 = anoxygenic

  25. Green and purple photosynthetic bacteria Purple system - like Photosystem II Green system - like Photosystem I

  26. Green and purple photosynthetic bacteria Use H2, H2S, S0 or organic molecules as electron donors Possess bacteriochlorophylls (absorb at longer wavelengths)

  27. Green and purple photosynthetic bacteria Possess only 1 photosystem  restricted to cyclic photophosphorylation Use ATP or proton motive force to reduce NAD+

  28. The dark reaction Involves the fixing of CO2 (conversion into organic material) Known as the Calvin or the Calvin-Benson cycle Alternate CO2 fixing pathways exist

  29. The dark reaction Divided into three phases 1. Carboxylation phase 2. Reduction phase 3. Regeneration phase

  30. Carboxylation phase Ribulose-1,5-bisphosphate carboxylase adds CO2 to ribulose-1,5-bisphosphate (RuBP) Forms 2 molecules of 3-phosphoglycerate (PGA)

  31. Reduction phase PGA is reduced to glyceraldehyde-3-phosphate using NADPH as an electron donor

  32. Regeneration phase Regenerates RuBP and produces carbohydrates Involves transketolase and transaldolase reactions 6RuBP + 6CO2 12 PGA 12 PGA  6RuBP + fructose-6-P

  33. The dark reaction 6CO2 + 18 ATP + 12 NADPH + 12H2O  glucose + 18 ADP + 18 Pi + 12 NADP+

  34. Biosynthesis Also known as anabolism Construction of complex molecules from simple precursors Energy derived from catabolism used in biosynthesis

  35. Principles governing biosynthesis Large macromolecules (proteins, nucleic acids, polysaccharides) are made up of a few small structural units (monomers) Cells often use the same enzymes for anabolism and catabolism In amphibolic pathways, some steps may be catalyzed by 2 different enzymes (one for anabolism, one for catabolism)

  36. Principles governing biosynthesis

  37. Principles governing biosynthesis Some biosynthetic reactions are coupled to the breakdown of ATP so as to drive them in the forward direction Anabolic and catabolic pathways often use different cofactors (e.g. NADH as electron acceptor and NADPH as electron donor)

  38. Gluconeogenesis Microorganisms that cannot perform photosynthesis must synthesize sugars from reduced organic compounds Synthesis of glucose from noncarbohydrate precursors known as gluconeogenesis Reversal of glycolysis

  39. Gluconeogenesis Three steps are irreversible and must be catalyzed by other enzymes Synthesizes both glucose and fructose  other sugars synthesized from glucose and fructose

  40. Nucleoside diphosphate sugars Some sugars are synthesized while attached to a nucleoside diphosphate Most common nucleotide diphosphate sugar is uridine diphosphate glucose (UDPG)

  41. Nucleoside diphosphate sugars UDPG can be used to synthesize galactose or glucuronic acid Nucleoside diphosphate sugars play a central role in the synthesis of starch and glycogen

  42. Phosphorus assimilation Phosphate required for synthesis of nucleic acids, proteins, phospholipids, ATP and coenzymes Inorganic phosphate can be assimilated by incorporating it into ATP in one of three ways: Photophosphorylation Oxidative phosphorylation Substrate level phosphorylation

  43. Phosphorus assimilation Microorganisms may also hydrolyze phosphate from organic phosphates

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