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LECT 6. RESPIRATION

COMPETENCIESStudents, after mastering materials of thepresent lecture, should be able:1. To explain the process of respiration (the oxidation of

substrates particularly carbohydrates or the synthesisof metabolic energy used for plant growth andmaintenance)

2. To explain reactions, enzymes and products involvedthe respiration

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Glucose is the most commonlycited substrate of respiration

Glucose serves as the primaryenergy source for the brain andis also a source of energy forcells throughout the body

GUT4: glucosetransporters(protrein)

Blood glucose isnormally maintainedbetween 70 mg/dland 110 mg

http://www.ans.kobe-u.ac.jp/english/gakka/seibutsukinou/seibutu.html

LECTURE FLOW QUESTIONS

SUMMARY OF RESPIRATION

1. DEFINITION

2. THE SITE OF RESPIRATION

3. MAIN STEPS OF RESPIRATION

4. COMPARING ENERGY YIELD

5. FEEDBACK CONTROL OF RESPIRATION

6. RESPIRATION AND PLANT CARBON BALANCE

7. FACTORS AFFECTING RESPIRATION

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QUESTIONS1. What is the importance of respiration2. How many steps does the respiration have3. What is the first and second step of respiration4. Where does the glycolysis take place5. Where does the TCA cycle take place6. Where does the Electron Transport Chain take place7. What is the compound exported from cytosol to

mitochondria in the respiration8. What is the final acceptor of electrons in the respiration9. How many NADP does the glycolysis produce10. How many NADP does the TCA cycle produce11. How many ATP does the glycolysis produce12. How many ATP does the TCA cycle produce13. What is the meaning of ADP:O ratios

QUESTIONS

14. What is the ADP:O ratio of FADH2

15. How many ATP does the respiration produces totally16. How efficient is the respiration in the conversion of

energy17. What does it mean by feedback control of respiration18. How is the effect of tissue stage of development on

the respiration19. How is the effect of O2 on the respiration20. How is the effect of CO2 on the respiration21. How is the effect of plant injury on the respiration22. How is the foliar respiration of trees in term of height23. How is the response of foliar respiration to nitrogen24. How is the woody respiration in term of wood

diameter

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Respiration = Dark Respiration

Citric acid cycle (“Krebs cycle”) Electron transport and ATP synthesis

Respiration and carbon economy ofwhole plants

Hans Krebs, 1953 Nobel Prize

Biochemistry of respiration Glycolysis (“glyco”= sugar; “lysis”= “untie”)

CH2O + O2 → CO2 + H2O + energy

Glycolysis – break a 6-carbon sugar into two 3-Carbon sugars (triose phosphate) – takes someenergy – then strip electrons from these 3-Csugars – releases a bit of energy in the form ofATP and NADH. “Leftover” products: 3C sugarsPyruvate and Malate (still embody substantial freeenergy)

Citric acid/krebs cycle complete oxidation ofpyruvate/malate to produce CO2, H2O, reducingpower (NADH, FADH2) and ATP

Electron Transport Chain launder NADH, FADH2

to ATP across inner mitochondrial membrane andto Membrane)

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1. DEFINITION

1. Respiration is the process whereby theenergy stored in carbohydrates, producedduring photosynthesis, is released in acontrolled manner.

2. The energy (free energy) released duringrespiration is incorporated into a form (ATP)that can be readily utilized for themaintenance and development of the plant.

What is respiration ?

3. Respiration is tightly coupled to otherpathways

Biosynthesis of Nucleotides

Biosynthesis of Proteins

Biosynthesis of Lipids

Biosynthesis of Cell wall components

Biosynthesis of Phytohormones

Biosynthesis of Plant pigments

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2. THE SITE OF RESPIRATION

1. Mitochondria are the mainsite of ATP synthesis ineukaryote cells and as suchare vital for the health andsurvival of the cell

Where does the respiration take place?

2. From a chemical standpoint, respiration is mostcommonly expressed in terms of the oxidation ofthe six-carbon sugar glucose.

3. This equation represents a coupled redoxreaction that oxidizes completely glucose to CO2

with oxygen serving as the ultimate electronacceptor and reduced to water.

4. The substrate for respiration most commonlycited, in a functioning plant cell, is glucose that isactually derived from such sources as theglucose polymer starch, the disaccharidesucrose, fructose-containing polymers(fructosans), and other sugars, as well as lipids(primarily triacylglycerol), organic acids, and onoccasion, proteins

5. The amount of energy release is roughly 2880 kJ(686 kcal) per mole (180 g) of glucose oxidizedthat is coupled to the synthesis of ATP.

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• Two membranes

• Inner membrane invaginated

• Numbers of mitochondria per cell

vary but usually 100s/cell

• Matrix contains the TCA cycle(and other) soluble enzymes

• Inner membrane containsmetabolite transporters and theelectron transport chain

Mitochondria have their own DNA and Ribosomes

Mitochondrial DNA• Mitochondria have

some of their own DNA,ribosomes and tRNA;22 tRNAs & rRNAs (16Sand 12S), somitochondria can makemany of their ownproteins.

• The DNA is circular and lies in the matrix in structurescalled "nucleoids". Each nucleoid may contain 4-5 copiesof the mitochondrial DNA (mtDNA).

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3. MAIN STEPS OF RESPIRATIONWhat are the stages of glucose oxidation ?

The reactions ofglucose oxidationcan be subdividedinto three stages:

1. Glycolysis

2. The tricarboxylicacid (TCA) cycle,and

3. The electrontransport chain(terminal oxidation)

Anaerobic Respiration

C6H12O6 + O2→2 CH2O5 + 2 H2O + 2 ATPor

Glucose + Oxygen →2 Ethanol + 2 Water + 2 ATP

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3 Main Respiration Steps

1. Glycolysis

2. Glucose (C6H12O6)Pyruvate (C3H4O3): Breakdown ofGlucose to a 3-Carbon Compound Called calledPyruvate

• This occurs in Cytosol• Some ATP and NADH

Are also Formed– Storage Energy Molecules

• NADH is Formed fromNAD

• Similar Type of Energy-Storing Rx asNADP + H2 →NADPH2– NAD + H →NADH

2. Krebs Cycle/Citric Acid Cycle ‘Tricarboxylic acid Cycle (TCA Cycle)’ occurs in

Mitochondrial Matrix A Cyclic Series of Rxs that Completely Break

down Pyruvate to CO2 and Various CarbonSkeletons

This is the step where CO2 isgiven off by the Plant

Skeletons Are Used in otherMetabolic Pathways to Makevarious Compounds Proteins Lipids Cell Wall Carbohydrates DNA Plant Hormones Plant Pigments Many other Biochemical Compounds

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3. Electron Transport Chain ‘Oxidative Phosphorylation’ Series of proteins in the mitochondria helps

transfer electrons (e-) from NADH to oxygen Releases a lot of energy

This occurs onMitochondrial InnerMembrane (Proteins Boundto Membrane)

Released energy is used to drive the reaction ADP +P → ATPMany ATP are made

Oxygen is required for this step

Water is produced

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Overview of aerobicrespiration

GLYCOLISIS:SUCROSE or STARCHPYRUVATE

1. Sucrose Glucose + Fructose2. Starch Glu 1-P3. Glu 1-P Glu 6-P4. Glucose Glu 6-P5. Fructose Fruc 6-P6. Glu 6-P Fruc 6-P7. Fru 6-P Fruc 1,6-P8. Fru 1,6-P Dihydroxyacetone

P + Glyceraldehyde 3-P

9. Glyceraldehyde 3-P 1,3Bisphosphoglycerate

10. 1,3 Bisphosphoglycerate 3phosphoglycerate

11. 3 phosphoglycerate 2phosphoglycerate

12. 2 phosphoglyceratePhosphoenol pyruvate(PEP)

13. PEP Pyruvate

Anaerobic Respiration (Fermentation)Pyruvate Lactate or Pyruvate Ethanol

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Citric Acic Cycle (Krebs Cycle)1. Pyurvate Acetyl-CoA2. Acetyl-CoA Citrate3. Citrate Isocitrate4. Isocitrate α-ketoglutarate5. α-ketoglutarate Succinyl-

CoA6. Succinyl-CoA Succinate7. Succinate Fumarate8. Fumarate Malate9. Malate Oxaloacetate

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Complex I: NADH Dehydrogenase oxidizes NADH transfers e- to Ubiquinone (UQ) pumps 1H+ per e-

Complex II: Succinate Dehydroganase oxidation of succinate (from citric acid cycle) e- are transferred via FADH2

does not pump protons Complex III: Cytochrome bc1 complex

oxidizes reduced UQ (= ubiquinol) pumps 1H+ per e-

Complex IV: Cytochrome c oxidase reduces O2 to H2O pumps 1H+ per e-

Complex V: ATP synthase uses electrochemical proton gradient to synthesize ATP

The electron transport chain (terminal oxidation)

-complex I is a NADH-ubiquinone reductase-complex II is succinate

dehydrogenase (part of theTCA cycle)-complex III is the

ubiquinone -cytochrome creductase-complex IV is cytochrome

oxidase

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http://www.bmb.leeds.ac.uk/illingworth/oxphos/

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Substrate ADP/O

NADH (Malate) 2.4-2.7

NADH (Succinate) 1.6-1.8

NADH (External) 1.6-1.8

NADH (Ascorbate)* 0.8-0.9

Table. ADP/O ratios in isolated plant mitochondria

*Artificial electron donorADP/O = number of ATPs synthesized per two electrons transferredto oxygen

4. COMPARING ENERGY YIELD Glycolysis (per glucose): Net: 2ATP, 2NADH

Krebs (per glucose): 2ATP, 8NADH, 2FADH2

Total: 4ATP, 10NADH equivalents ATP:NADH ratio ~3 in Mitochondria Thus 4ATP + 10NADHx3 = 34 ATPs per glucose

(more or less) (34 x 50.2 kJ/mol)/(2880 kJ/mol )= 59% conversion

efficiency! (versus around 4% for glycolysis alone)

1 mol glucose givesΔGo = -2880 kJ/mol

1 mol ATP takesΔGo = 50.2 kJ/mol

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ENERGY PRODUCTIONSite/Process Quantity ADP/O ATP

• Glycolysis 2 ATP 2• TCA Cycle 2 ATP 2• Cytosol 2 NADH 2.5 5• Mitochondrial Matrix 8 NADH 2.5 20• Mitochondrial Matrix 2 FADH2 1.5 3

TOTAL 32Conversion Efficiency(32 x 50.2 kJ/mol)/(2880 kJ/mol )= 55.8%

Complex IV, the cytochrome c oxidase, is specifically inhibited by cyanide (CN-),azide (N3

-), and carbon monoxide (CO). Cyanide and azide bind tightly to theferric form of cytochrome a3, whereas carbon monoxide binds only to the ferrousform. The inhibitory actions of cyanide and azide at this site are very potent,whereas the principal toxicity of carbon monoxide arises from its affinity for theiron of hemoglobin

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5. FEEDBACK CONTROL OF RESPIRATION

Demand regulation Low amounts of ADP dramatically reduce the rate

of mitochondrial respiration The rate of respiration increases when energy

demand for growth, maintenance and transportprocesses is high that consume rapidly ATPleading to the production of ADP

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RESPIRATION AND PLANT CARBONBALANCE

• On a whole-plant basis,respirationconsumes from30% to 70% oftotal fixedcarbon

• Leaves accountfor about half ofthe total

FACTORS AFFECTING RESPIRATION1. Kind of Cell or Tissue. Young and developing cells (meristematic areas) usually have higher

respiration rates. Developing and ripening fruit and seeds, too. Older cells and structural

cells respire at lower rates2. Temperature Respiration generally has higher optimum and maximum temps than PS Rxs

3. Oxygen Low O2 can reduce aerobic respiration and increase anaerobic respiration Low O2 can reduce photorespiration

4. CO2 Higher CO2 levels reduce rate of respiration (feedback inhibition). Seldom

occurs except when O2 levels are limited (flooded, compacted soils)5. Plant Injury Injury will Increase Respiration

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Kind of Cell or Tissue

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Temperature Effect

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