9/1/2016
1
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
29/1/2016
9/1/2016
2
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
9/1/2016
3
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
9/1/2016
4
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)
9/1/2016
5
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
9/1/2016
6
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.
9/1/2016
7
• 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).
9/1/2016
8
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
9/1/2016
9
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
9/1/2016
10
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
9/1/2016
11
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
9/1/2016
12
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
9/1/2016
13
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
9/1/2016
14
http://www.bmb.leeds.ac.uk/illingworth/oxphos/
9/1/2016
15
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
9/1/2016
16
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
9/1/2016
17
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
9/1/2016
18
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
9/1/2016
19
Kind of Cell or Tissue
9/1/2016
20
Temperature Effect
9/1/2016
21