respiration and photosynthesis Lecture.pptx

lecture note

1. c3,c4,cam plants Presented By, Dr.Thirunahari Ugandhar

2. Aerobic respiration Aerobic respiration is completed in Glycolysis Oxidative carboxylation (Acetylation) Krebs cycle Electron transport system

3. Glycolysis The sequence of reactions in which glucose (6C) is broken down into two molecules of pyruvic acid(3C). Also called as EMP pathway named after their discoverers Embden, Meyerhoff, and Paranas. 1 st step in breakdown of glucose. Does not require presence of oxygen & there is no output of carbon dioxide. Occurs in cytoplasm of cell. Involves series of 10 reaction, each controlled by a specific enzyme.

4. The reactions are studied in three groups: Activation or phosphorylation of glucose molecule. Cleavage or fragmentation Oxidation.

5. Activa t i o n

6. Activation or Phosphorylation of Glucose Phosphorylation of glucose Glucose is converted to Glucose 6- phosphate Isomerisation Glucose 6- phosphate isomerised to Fructose 6-phosphate. Second phosphorylation Fructose 6-phosphate is phosphorylased to Fructose 1, 6- diphosphate by enzyme Phosphofructokinase(PFK).

7. Cleavage or Fragmentation Cleavage Fructose 1, 6 bi phosphate is an unstable compound and splits to produce 3C compounds 3PGAL and DHAP. Isomerisation Glycolysis utilizes only PGAL, therefore DHAP is isomerised to 3PGAL

8. Oxidation Oxidative phosphorylation(Dehydrogenation): 3PGAL is oxidized by removal of Hydrogen(H 2 ) and simultaneous phosphorylation of the product resulting in 1,3 Di PGA ATP synthesis: 1,3 Di PGA is converted to 3 PGA by release of one phosphate group. Isomerization: Phosphate group at 3 rd carbon is shifted to 2 nd i.e. 3 PGA to 2PGA.

9. 9. Dehydration : o 2 PGA loses a molecule of water and gets converted to PEPA 10. ATP synthesis (formation of Pyruvic acid) o PEPA is converted to Pyruvic acid by removal of phosphate group.

10. Net reaction of Glycolysis + 2 ADP +2 NAD + 2 C 3 H 4 O 3 + 2 ATP +2NADH + C 6 H 12 O 6 H + Net gain of ATP + • = From 6 A 2 T N P ADH 2 Direc 4 tl A y T fo P rmed U 2 ti A liz T e P d Net 8 ga A in TP P y ruvic acid

11. Fate of Pyruvic Acid Glucose Glycolysis Pyruvic acid Anaerobic res p irati o n Aerobic res p irati o n O 2 is used O 2 is not used

12. Acetylation Conversion of Pyruvic acid into Acetyl Co- A Reaction starts in cytoplasm and completes in mitochondria Pyruva te (3C) Co A + NAD + CO 2 + NADH 2 Acetyl Co- A (2C) Pyruvic dehydrogenas e

13. Kreb’s cycle Also called TCA or Citric Acid cycle. Stepwise, cyclic complete oxidation and decarboxylation of Pyruvic acid into CO 2 AND H 2 O with release of energy. Named after Hans Krebs who traced the sequence of reactions. Takes place in matrix of mitochondria. Des not consume ATP molecules.

14. The reactions are as follows: Condensation: Acetyl Co-A (2C) combines with Oxaloacetic acid (4C) in presence of water to form Citric acid(6C). Isomerisation: Citric acid first dehydrates to form Cis Aconitic acid and then rehydrates to form Isocitric acid(6 C). Dehydrogenation: Isocitric acid oxidizes to form Oxalosuccinic acid(6C). Decarboxylation: With release of a CO2 Oxalosuccnic acid converts to α-Keto glutaric acid(5C).

15. 5. Oxidative decarboxylation: α- Ketoglutaric acid oxidizes & decarboxylates and the product combines with Co-A to form Succinyl Co-A (4C). ATP synthesis: Succinyl Co-A is hydrolysed to Succinic acid(4C). Dehydrogenation: Succinic acid is oxidized to Fumaric acid (4C). Hydration: Fumaric acid is converted to Malic acid (4C) by addition of water. Malic acid is then oxidised to form Oxaloacetic acid(4C).

16. Net gain of ATP 8 NADH 2 - 24 ATP 2FADH 2 - 4 ATP Direct synthesis - 2 ATP Total gain of ATP - 30 ATP ATP synthesis through ETS

17. Electron Transport System Final step of aerobic respiration. Most ATP and metabolic water generated in this step. Located in inner mitochondrial member(cristae & oxysomes). Individual members are called electron carriers. Electrons from NADH and Succinate pass through the ETS to oxygen, which is reduced to water.

18. NADH Complex I UQ Cytochrome c Complex IV O 2 Complex II Complex III Succinate

19. 2H + + 2e - + ½ O 2 H 2 O NADH 2 or FADH 2 NAD or FAD + 2H + + 2e - Formation of metabolic water

20. Steps Reduced coenz y mes ATP through ETS Dir e ct ATP Total ATP 1. Glycolysis 2 NADH 2 2 2NADH X 3= 6ATP 2 ATP 8 ATP 2. Ace t yla t ion 2 NADH 2 2 2NADH X 3 = 6 ATP - 6 ATP 3. Krebs cycle 6 NADH 2 2 NADH X 3 = 18 ATP 2 ATP 24 ATP 2 FADH 2 FADH 2 X 2 = 4 ATP C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O + 38 ATP

21. Significance of Aerobic Respiration 1 glucose molecule produces 38 ATP molecules. Glucose molecule consists 686 k.cal energy. Of these only 277.4 k.cal energy (38 X 7.3 k.cal) is conserved in ATP. Remaining energy is lost as heat energy. Efficiency of this respiration is 40%.

22. Anaerobic respiration The partial\ incomplete oxidation of organic food in the absence of atmospheric oxygen is called Anaerobic respiration. Organisms performing anaerobic respiration are called anaerobes. In micro organisms it is known as fermentation. No exchange of gases. Only 2 ATP molecules are formed.

23. Mechanism It is completed in 3 main steps. Glycolysis Decarboxylation Reduction

24. Glycolysis First step is similar to glycolysis of aerobic respiration. C 6 H 12 O 6 + 2ADP +2NAD + 2C 3 H 4 O 3 +2 ATP +2NADH+H +

25. Decarboxylation Pyruvic acid is decarboxylated to form Acetaldehyde (2C) and CO 2 by enzyme pyruvate decarboxylase. 2CH 3 CO COOH 2CH 3 CHO + 2 C O 2 Pyruvate D e c a rbo x y las e Pyruvic acid Acetaldehyde

26. Reduction Acetaldehyde Ethyl Al c ohol Acetaldehyde is reduced to Ethyl Alcohol by NADH 2 formed in Glycolysis with the help of enzyme Alcohol Dehydrogenase. Alcohol D e h y dro g e n a se

27. Significance of Respiration Release of energy Synthesis of ATP Stepwise release of energy Growth and development Energy for biosynthesis Role of intermediates Balance of CO 2 & O 2 Fermentation

28. Thank you

29. Photosynthesis Live Reaction

30. C 3 Plants Called C3 because the first product of photosynthesis is a 3-carbon molecule. Most plants are C3,usually on dicot plant . C3 photosynthesis is a multistep process in which the carbon from CO2 is fixed into stable organic products, it occurs in virtually all leaf mesophyll cells. Rubisco, the enzyme involved in photosynthesis, is also the enzyme involved in the uptake of CO2. Photosynthesis takes place through out the leaf. Advantage of C3 : -More efficient than C4 plants under cool and moist conditions and under normal light because fewer enzymes and no specialized anatomy.

31. Comparison # C 3 : 1. Plants operate Calvin Cycle only in all green cells. 2. There is only one CO 2  acceptor, i.e., RuBP. 3. The first stable product of photo­synthesis is PGA (a C 3  acid). 4. “ Kranz anatomy” is not found. There is no chloroplast dimorphism. They have well defined grana with both PS-I and PS-II. 5. There is no CO 2  concentrating device. Fixation and assimilation of C takes place only through Calvin cycle in the day. So, there is no decarboxylation mechanism . : 6. Photorespiratory toss of photo- synthates is very prominent due to dual action of rubisco and lack of PEPcase . Up to 40% of photosynthates may be lost. .

32. 7. CO 2  compensation point is 40-100 µ|| -1 . 8. Intracellular CO 2  concentration in light is 200 µ|| -1 . 9. Stomatal frequency is 2000 – 31000. 10. Water use efficiency is 1-3 gCO 2  fixed/kg water transpired. 11. Maximum growth rate is 5-20g m -2  d -1 . 12. Maximum productivity 10-30 t ha -1 y -1 . 13. Typical species of economic impor­tance are wheat, barley, rice, potato. 14. 89% world flora (in species number). 15. Widely distributed and dominant in forests.

33. Called C4 because the first initial photosythesis product is a 4-carbon compound. C4 photosynthesis occurs in the more advanced plant taxa and is especially common among monocots, such as grasses and sedges C4 photosynthesis represents a biochemical and morphological modification of C3 photosynthesis to reduce Rubisco oxygenase activity and thereby increase photosynthetic rate in low CO2 environments

34. Photosynthesis takes place in inner cells Surrounding the bundle sheath cells are mesophyll cells in which a much more active enzyme, Phosphoenolpyruvate (PEP) Carboxylase Uses PEP Carboxylase for the enzyme involved in the uptake of CO2. This enzyme allows CO2 to be taken into the plant very quickly, and then it delivers the CO2 directly to Rubisco for photosynthesis The additional cost of C4 photosynthesis is the adenosine triphosphate (ATP) requirement associated with the regeneration of PEP from pyruvate. C4 photosynthesis occurs primarily within monocotyledonous plants

35. Advantage of C4: Photosynthesis effecient than C3 plants under high light intensity and high temperatures because the CO2 concentration is high, not allowing it to grab oxygen and undergo photorespiration. Has better water use efficiency because PEP Carboxylase brings in CO2 faster and so does not need to keep stomata open as much (less water lost by transpiration) for the same amount of CO2 gain for photosynthesis.

36. Comparison # C 4 : 1. Plants operate C 4  cycle in MC in addition to C 3  cycle operating in BSC. 2. There are two C0 2  acceptors — PEP and RuBP. 3. The first stable product is malate or aspartate (aC 4 acid). : 4. The leaves show “Kranz anatomy”. The chloroplasts are dimorphic. The MC chloroplasts are granal whereas the BSC chloroplasts are agranal lacking PS-II. 5. Plants are specially characterized by CO 2  concentrating mechanism. So, there is initial carboxylation in MC followed by decarboxylation in BSC. Both are occurring in same time (day) but separated in space. 6. Photorespiration cannot be detected due to the high activity of PEP case in MC. The C 4  cycle gears the C 3  cycle by pumping C0 2  in BSC. Rubisco cannot behave as oxygenase. 7. 0-10 µ|| -1 .

37. 8 . 100 µ|| -1 . 9. 10000-16000. 10. 2 – 5 g of CO 2  fixed/kg of water transpired. 11. 40-50g m -2 d -1 . 12. 60 – 80 t ha  -1  y -1 . 13. Maize, millet, sugarcane, sorghum. 14. < 1%. 15. Warm to hot open sites (grassland).

38. Comparison # CAM: 1 . Plants operate only C 3  cycle in MC for carbon assimilation. 2. Same as C 4 . 3. The initial fixation product is malate in dark, which remains stored in vacuole. 4. No “Kranz anatomy” is found. The chloroplasts are not dimorphic. 5. Plants show CO 2  accumulating device as malate during night as they are adapted to arid zone. So, acidification and de-acidification occur in the same space (MC) but separated in time. The former takes place in dark while the latter takes place in light. 6. Photorespiration cannot be detected as the stomata remain closed during day. The photo-respiratory CO 2  cannot escape instead is re-fixed by Rubisco.