RESPIRATION IN PLANTS

 

Oxidative decarboxylation:

• Pyruvic acid formed in the cytoplasm enters into mitochondria.
• Pyruvic acid is converted into Acetyl CoA in presence of pyruvate dehydrogenase complex.
• The pyruvate dehydrogenase catalyses the reaction require several coenzymes, including NAD⁺ and Coenzyme A.
• During this process two molecules of NADH are produced from metabolism of two molecules of pyruvic acids (produced from one glucose molecule during glycolysis).
• The Acetyl CoA (2c) enters into a cyclic pathway, tricarboxylic acid cycle.

Tri Carboxylic Acid Cycle (Krebs cycle) or Citric acid Cycle :

• This cycle starts with condensation of acetyl group with oxaloacetic acid and water to yield citric acid.  This reaction is catalysed by citrate synthase.
• Citrate is isomerised to form isocitrate.
• It is followed by two successive steps of decarboxylation, leading to formation of α-ketoglutaric acid and then succinyl-CoA.
• In the remaining steps the succinyl CoA oxidized into oxaloacetic acid.
• During conversion of succinyl CoA to succinic acid there is synthesis of one GTP molecule.
• In a coupled reaction GTP converted to GDP with simultaneous synthesis of ATP from ADP.
• During Krebs cycle there production of :
  • 2 molecule of CO₂
  • 3 NADH₂
  • 1 FADH₂
  • 1 GTP.
• During the whole process of oxidation of glucose produce:
  • CO₂
  • 10 NADH₂
  • 2 FADH₂
  • 2 GTP.( 2 ATP)

Electron transport system and oxidative phosphorylation :

• The metabolic pathway, through which the electron passes from one carrier to another, is called Electron transport system.
• it is present in the inner mitochondrial membrane.
• ETS comprises of the following:
  • Complex I – NADH Dehydrogenase.
  • Complex II – succinate dehydrogenase.
  • Complex III – cytochromes bc1
  • Complex IV – Cytochromes a-a₃ (cytochromes c oxidase).
  • Complex V – ATP synthase.
  
  
• NADH₂ produced in the citric acid cycle oxidized by NADH Dehydrogenase, and electrons are then transferred to ubiquinone located in the inner membrane.
• FADH₂ is oxidized by succinate dehydrogenase and transferred electrons to ubiquinone.
• The reduced ubiquinone is then oxidized with transfer of electrons to cytochrome c via cytochromes bc1 complex.
• Cytochrome c is small protein attached to the outer surface of the inner membrane and acts as a mobile carrier for transfer electrons from complex III and complex IV.
• When electrons transferred from one carrier to another via complex I to IV in the electron transport chain, they are coupled to ATP synthase for the synthesis of ATP from ADP and Pi.
• One molecule of NADH₂ gives rise to 3 ATP.
• One molecule of FADH₂ gives rise to 2ATP.
• Oxygen plays a vital role in removing electrons and hydrogen ion finally production of H₂O.
• Phosphorylation in presence of oxygen is called oxidative phosphorylation.

Total ATP Production -

Process Total ATP produced :

• Glycolysis 2ATP + 2NADH₂ (6ATP) = 8ATP
• Oxidative decarboxylation 2NADH₂  (6ATP) = 6ATP
• Krebs’s Cycle 2GTP (2ATP) + 6NADH₂ (18ATP) + 2FADH₂ (4ATP) = 24 ATP
• Energy production in prokaryotes during aerobic respiration = 38 ATP
• Energy production in eukaryotes during aerobic respiration = 38 − 2 = 36 ATP
• (2ATP are used up in transporting 2 molecule of pyruvic acid in mitochondria.)

Abbreviations :

ATP −          Adenosine tri phosphate

ADP −         Adenosine di phosphate

NAD −         Nicotinamide Adenine dinucleotide

NADP −       Nicotinamide Adenine dinucleotide Phosphate

NADH −       Reduced Nicotinamide Adenine dinucleotide

PGA −          Phosphoglyceric acid

PGAL −        Phospho glyceraldehyde

FAD −          Flavin adenine dinucleotide

ETS −          Electron transport system

ETC −          Electron transport chain

TCA −          Tricarboxylic acid

OAA −          Oxalo acetic acid

FMN −          Flavin mono nucleotide

PPP −          Pentose phosphate pathway

CBSE Biology (Chapter Wise) Class XI ( By Mr. Hare Krushna Giri ) 
Email Id : [email protected]