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BOTANY DEPARTMENT Topic: Respiration of plants K.Bhargava sai



Definition :

Definition Respiration is a catabolic, enzyme mediated oxidative process by which the c-c bonds of the materials like carbohydrates fats, amino acids and organic acids broken down to release considerable amount of energy hence an Exergonicprocess

Types of Respirations:

Types of Respirations

Aerobic respiration:

Aerobic respiration Aerobic respiration. It is common among all higher plants. Glucoses completely oxidized. More energy is release. The ATP out put is 36 molecules. The end products are co2and H2o

Anaerobic respiration :

Anaerobic respiration Generally found in lower organisms. Occurs in the absence of oxygen. Glucose is partially oxidized. Less energy is released (56-Kcl). The ATP output is only 2 molecules. The end product are co2 and ethylalchohol, acetic and lactic acid.

Mitochondria :

Mitochondria A mitochondria are the cell organelles associated with the process of respiration. Mitochondria are membrane-enclosed organelles distributed through the cytosol of most eukaryotic cells. Their number within the cell ranges from a few hundred to, in very active cells, thousands. Their main function is the conversion of the potential energy of food molecules into ATP. Mitochondria have: an outer membrane that encloses the entire structure an inner membrane that encloses a fluid-filled matrix between the two is the intermembrane space the inner membrane is elaborately folded with shelf like cristae projecting into the matrix . a small number (some 5–10) circular molecules of DNA

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This electron micrograph shows a single mitochondrion from a bat pancreas cell. Note the double membrane and the way the inner membrane is folded into cristae. The dark, membrane-bounded objects above the mitochondrion are lysosomes. The number of mitochondria in a cell can 1)increase by their fission (e.g. following mitosis); 2)decrease by their fusing together. (Defects in either process can produce serious, even fatal, illness.) Impermeable to ions and most other compounds In inner membrane knobs

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The Outer Membrane The outer membrane contains many complexes of integral membrane proteins that form channels through which a variety of molecules and ions move in and out of the mitochondrion. The Inner Membrane The inner membrane contains 5 complexes of integral membrane proteins: NADH dehydrogenase (Complex I) succinate dehydrogenase (Complex II) cytochrome c reductase (Complex III; also known as the cytochrome b-c 1 complex) cytochrome c oxidase (Complex IV) ATP synthase (Complex V) The Matrix The matrix contains a complex mixture of soluble enzymes that catalyze the respiration of pyruvic acid and other small organic molecules. Here pyruvic acid is 1)oxidized by NAD + producing NADH + H + 2)decarboxylated producing a molecule of carbon dioxide (CO 2 ) and a 2-carbon fragment of acetate bound to coenzyme A forming acetyl-CoA

Aerobic respiration :

Aerobic respiration Aerobic respiration leads to complete oxidation of glucose molecule, involving four different steps.

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Glycolysis:- this step is during on cytoplasm .glucose is participated initially the final out put is pyruvic acid. Oxidative decarboxylation of pyruvic acid:- this step is during on Mitochondrial matrix.the input is pyruvic acid the final out put is acetyl coenzyme-A. Krebs cycle:- In this step acetyl coenzyme-A is converted to co2,h2o And NADH & FADH2. Electron transport system:- this step is during on inner mitochondrial membrane. NADH & FADH2 are oxidised ,during this process is used to synthesize a large amount of ATP in a process known as oxidative phosphorylation The mechanism of aerobic respiration involves 6 oxidation reactions 1 in Glycolysis 1 in oxidation decarboxilation of pyruvic acid 4 in Krebs cycle Mechanism of aerobic respiration

Glycolysis :

Glycolysis “Glykys”=sweet And “Lysis”=splitting. Glycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+.

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1)Phospho relation The enzyme hexokinase phosphorylates (adds a phosphate group to) glucose in the cell's cytoplasm. In the process, a phosphate group from ATP is transferred to glucose producing glucose 6-phosphate. Glucose (C6H12O6) + hexokinase + ATP → ADP + Glucose 6-phosphate (C6H11O6P1) 2)Isomerisation The enzyme phosphoglucoisomerase converts glucose 6-phosphate into its isomer fructose 6-phosphate. Isomers have the same molecular formula, but the atoms of each molecule are arranged differently. Glucose 6-phosphate (C6H11O6P1) + Phosphoglucoisomerase → Fructose 6-phosphate (C6H11O6P1) 3)phosporilation The enzyme phosphofructokinase uses another ATP molecule to transfer a phosphate group to fructose 6-phosphate to form fructose 1, 6-diphosphate. Fructose 6-phosphate (C 6 H 11 O 6 P 1 ) + phosphofructokinase + ATP → ADP + Fructose 1, 6-diphosphate (C 6 H 10 O 6 P 2 )

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4) clevage The enzyme aldolase splits fructose 1, 6-diphosphate into two sugars that are isomers of each other. These two sugars are dihydroxyacetone phosphate and glyceraldehyde phosphate. Fructose 1, 6-diphosphate (C 6 H 10 O 6 P 2 ) + aldolase → Dihydroxyacetone phosphate (C 3 H 5 O 3 P 1 ) + Glyceraldehyde phosphate (C 3 H 5 O 3 P 1 ) 5) isomerisation The enzyme triose phosphate isomerase rapidly inter-converts the molecules dihydroxyacetone phosphate and glyceraldehyde phosphate. Glyceraldehyde phosphate is removed as soon as it is formed to be used in the next step of glycolysis . Dihydroxyacetone phosphate (C 3 H 5 O 3 P 1 ) → Glyceraldehyde phosphate (C 3 H 5 O 3 P 1 ) Net result for steps 4 and 5: Fructose 1, 6-diphosphate (C 6 H 10 O 6 P 2 ) ↔ 2 molecules of Glyceraldehyde phosphate (C 3 H 5 O 3 P 1 )

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6)oxidation The enzyme triose phosphate dehydrogenase serves two functions in this step. First the enzyme transfers a hydrogen (H - ) from glyceraldehyde phosphate to the oxidizing agent nicotinamide adenine dinucleotide (NAD + ) to form NADH. Next triose phosphate dehydrogenase adds a phosphate (P) from the cytosol to the oxidized glyceraldehyde phosphate to form 1, 3-diphoshoglyceric acid. This occurs for both molecules of glyceraldehyde phosphate produced in step 5. A. Triose phosphate dehydrogenase + 2 H - + 2 NAD + → 2 NADH + 2 H + B. Triose phosphate dehydrogenase + 2 P + 2 glyceraldehyde phosphate (C 3 H 5 O 3 P 1 ) → 2 molecules of 1,3-diphoshoglyceric acid (C 3 H 4 O 4 P 2 )

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7) dephosphorylation The enzyme phosphoglycerokinase transfers a P from 1,3-diphoshoglyceric acid to a molecule of ADP to form ATP. This happens for each molecule of 1,3-diphoshoglyceric acid. The process yields two 3-phosphoglyceric acid molecules and two ATP molecules. 2 molecules of 1,3-diphoshoglyceric acid (C 3 H 4 O 4 P 2 ) + phosphoglycerokinase + 2 ADP → 2 molecules of 3-phosphoglyceric acid (C 3 H 5 O 4 P 1 ) + 2 ATP 8) Intramolecular shift The enzyme phosphoglyceromutase relocates the P from 3-phosphoglyceric acid from the third carbon to the second carbon to form 2-phosphoglyceric acid. 2 molecules of 3-Phosphoglyceric acid (C 3 H 5 O 4 P 1 ) + phosphoglyceromutase → 2 molecules of 2-Phosphoglyceric acid (C 3 H 5 O 4 P 1 )

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9)Dehydration The enzyme enolase removes a molecule of water from 2-phosphoglyceric acid to form phosphoenolpyruvic acid (PEP). This happens for each molecule of 2-phosphoglyceric acid. 2 molecules of 2-Phosphoglyceric acid (C 3 H 5 O 4 P 1 ) + enolase → 2 molecules of phosphoenolpyruvic acid (PEP) (C 3 H 3 O 3 P 1 ) 10) dephosphorylation The enzyme pyruvate kinase transfers a P from PEP to ADP to form pyruvic acid and ATP. This happens for each molecule of PEP. This reaction yields 2 molecules of pyruvic acid and 2 ATP molecules. 2 molecules of PEP (C 3 H 3 O 3 P 1 ) + pyruvate kinase + 2 ADP → 2 molecules of pyruvic acid (C 3 H 4 O 3 ) + 2 ATP

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Summary In summary, a single glucose molecule in glycolysis produces a total of 2 molecules of pyruvic acid, 2 molecules of ATP, 2 molecules of NADH and 2 molecules of water. Although 2 ATP molecules are used in steps 1-3, 2 ATP molecules are generated in step 7 and 2 more in step 10. This gives a total of 4 ATP molecules produced. If you subtract the 2 ATP molecules used in steps 1-3 from the 4 generated at the end of step 10, you end up with a net total of 2 ATP molecules produced. For a detailed view of the 10 steps, see: Details of the 10 Steps of Glycolysis .

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Oxidative decarboxylation of pyruvic acid Two molecules of pyruvic acid produced at he end of glycolysis are transported through the inner mitochondrial membrane into the matrix by speciel transport protien is called “ Pyruvate Translocatore ” Once the pyruvic acid is inside the matrix, it is first decarboxilated and then oxidized finally it condenses with co-enzyme “A” to form acetyl co-”A” Witch is very popularly known as connecting link between glycolysis and krebs cycle The overall formation reaction of acetyl CoA may be represented as: pyruvic acid + CoA + NAD + ---> acetyl CoA + NADH + H + + CO 2 The above reaction is under the catalytic influence of multienzyme complex known as Pyruvic dehydrogense complex.

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Pyruvic dehydrogense complex is cluster of 3 enzymes

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For the formation of acetyle co-A, six factors are required. They are Mg 2+ ,FAD, NAD +, Thiamine pyrophosphate(TTP), Lipoic acid and co-enzyme-A. At the and of oxidative decarboxylation tow molecules of NADH + H + are released fore tow molecules of pyruvic acid .this mitochondrial NADH + H + enter into the electron transport system for the production of ATP Conversion of pyruvate to Acetyl CoA 2 per glucose (all of Kreb’s ) Oxidative decarboxylation Makes NADH -33.4kJ

Fates of Acetyl CoA:

Fates of Acetyl CoA In the presence of CHO an using energy Metabolized to CO 2 , NADH, FADH 2 ,GTP and, ultimately, ATP If energy not being used (Lots of ATP present) Made into fat If energy being used, but no CHO present Starvation Forms ketone bodies (see fat metabolism slides) Danger!

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Sir Hans Adolf Krebs (25 August 1900 – 22 November 1981) was a German-born British physicianand biochemist.[6] Krebs is best known for his identification of two important metabolic cycles: the urea cycleand the citric acid cycle. The latter, the key sequence of metabolic chemical reactions that produces energy in cells, is also known as the Krebs cycle and earned him a Nobel Prize in 1953.

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Kreb’s Cycle ( tricarboxylic acid (TCA)cycle, citric acid cycle) “The wheel is turnin ’ and the sugar’s a burning” Geography Krebs in mitochondrial matrix Aerobic phase (requires oxygen) Mitochondrion Outer membrane very permeable Space between membranes called intermembrane space (clever huh!) Inner membrane ( cristae ) Permeable to pyruvate , Impermeable to fatty acids, NAD, etc Matrix is inside inner membrane

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Makes ATP Makes NADH Makes FADH 2 Requires some carbohydrate to run Watch for reaction coupling Overall goal

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Ten Steps in Kreb’s Cycle

Kreb’s Cycle:

Kreb’s Cycle

Net From Kreb’s:

Net From Kreb’s Oxidative process 3 NADH FADH 2 GTP X 2 per glucose 6 NADH 2 FADH 2 2 GTP All ultimately turned into ATP (oxidative phosphorylation …later)

Citrate Synthase Reaction (First):

Citrate Synthase Reaction (First) Claisen condensation -32.2kJ

Aconitase Reaction:

Aconitase Reaction Forms isocitrate Goes through alkene intermediate ( cis-aconitate ) elimination then addition Hydroxyl moved and changed from tertiary to secondary (can be oxidized) 13.3kJ

Isocitrate Dehydrogenase:

Isocitrate Dehydrogenase All dehydrogenase reactions make NADH or FADH 2 Oxidative decarboxylation -20.9kJ Energy from increased entropy in gas formation

α-ketoglutarate dehydrogenase:

α - ketoglutarate dehydrogenase Same as pyruvate dehydrogenase reaction Formation of thioester endergonic driven by loss of CO 2 increases entropy exergonic -33.5kJ

Succinyl CoA synthetase:

Succinyl CoA synthetase Hydrolysis of thioester Releases CoASH Exergonic Coupled to synthesis of GTP Endergonic GTP very similar to ATP and interconverted later -2.9kJ

Succinate dehydrogenase:

Succinate dehydrogenase Dehydrogenation Uses FAD NAD used to oxidize oxygen-containing groups Aldehydes alcohols FAD used to oxidize C-C bonds 0kJ


Fumarase Addition of water to a double bond -3.8kJ

Malate Dehydrogenase:

Malate Dehydrogenase Oxidation of secondary alcohol to ketone Makes NADH Regenerates oxaloacetate for another round 29.7 kJ

Net From Kreb’s:

Net From Kreb’s Oxidative process 3 NADH FADH 2 GTP X 2 per glucose 6 NADH 2 FADH 2 2 GTP All ultimately turned into ATP (oxidative phosphorylation …later)

Electron transport system :

Electron transport system This represents the fourth and the final stage of aerobic respiration. From the earlier three steps of aerobic respiration a total of 12 high energy electron pairs are generated as:10-NADH and 2- FADH 2 for each molecule of glucose.

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The electron transport chain Mitochondrial Complexes

Mitochondrial Complexes:

Mitochondrial Complexes NADH Dehydrogenase Succinate dehydrogenase CoQ-cyt c Reductase Cytochrome Oxidase

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ATP synthesize

Total Energy per glucose:

Total Energy per glucose Cytosol Glycolysis 2 NADH 2 ATP Mitochondrion Pyruvate dehydrogenase 2 NADH Krebs 6 NADH 2 FADH 2 2 GTP

Total Energy/glucose:

Total Energy/glucose In mitochondrion: Each NADH makes 2.5 ATP Each FADH 2 makes 1.5 ATP GTP makes ATP So… From in mitochondrion 8 NADH X 2.5 ATP/NADH = 20 ATP 2 FADH 2 X 1.5 ATP/FADH 2 = 3 ATP 2 GTP X 1 ATP / GTP = 2 ATP TOTAL in mitochondrion 25 ATP

Total Energy/ glucose:

Total Energy/ glucose Cytosol 2 ATP 2 NADH NADH can’t get into mitochondrion In eukaryotes two pathways, transferred to FADH 2 get 1.5 ATP/ FADH 2 Or transferred to NADH Get 2.5 ATP/ NADH (Not a problem in prokaryotes (why?)) 2 NADH X 1.5 ATP = 3 ATP Or 2 NADH X 2.5 ATP = 5 ATP + =2 ATP Total 3+ 2 or 5 + 2 so either 5 or 7


ATP/glucose Eukaryotes Mitochondrial: 25 ATP Cytosolic: 5 or 7 ATP Total 30 or 32 ATP/glucose 30 ATP X 7.3kcal X 4.18 kJ = 915 kJ ATP kcal If 32 ATP = 976 kJ Prokaryotes 32 ATP X 7.3kcal X 4.18 kJ = 976 kJ ATP kcal



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