🌞 Mechanism

Glycolysis, Link Reaction, Kreb Cycle, ETS

Mechanism of Respiration

  • 1st and common stage in respiration in called Glycolysis or EMP Pathway (Embden–Meyerhoff-Parnass) after the name of German scientists who traced the reaction steps.
  • EMP pathway results in two molecules of Pyruvic acid.
  • Second stage is different in the two types of respiration.

I. Glycolysis or EMP Pathway

  • Glycolysis has two phases:
    • 1st Phase: Consumption of ATP (2) i.e. Endothermic
    • 2nd Phase: Production of ATP (4) i.e. Exothermic
  • 1st Phase of Glycolysis
  1. Purpose: Phosphorylation of Glucose (i.e. addition of Phosphate PO4)
  2. Requirements: Enzyme (3) + ATP (2)
  3. Reactions
  • All reactions of glycolytic pathway are reversible.

Summary of Glycolysis

  • Products of Glycolysis
    • 2 Molecules of Pyruvic Acid (partially oxidised) and further will be oxidised through Link and Krebs cycle.
    • 2 Molecule of NADH2: Further will be used for electron transport system to release H2O.
    • ATP: Energy for any cell work
      • Production - 4 ATP
      • Consumption β€” 2 ATP
      • Net Production: 2 ATP in glycolysis
  • But 2 molecules of NADH2 will be oxidized aerobically to yield 6 molecules of ATP. Thus total molecules of ATP through glycolysis in presence of O2 will be 8 instead 2.
  • Pyruvic acid are obtained through partial oxidation of glycolytic path-way have two fates:
  • The first fate, which occurs in the absence of oxygen is called anaerobic respiration (Fermentation) and the 2nd fate which occurs in the presence of oxygen is called aerobic respiration or simply respiration.

Anaerobic respiration = Fermentation

  • Fermentation is done by some fungi and some bacteria.
  • In the absence of O2, NADH2 formed during glycolysis can’t be reoxidised by O2, hence for continuous supply of NAD is required for operation of glycolysis.
  • There are two important ways:
  • The formation of ethanol (Ethyl alcohol) in the absence of O2 is called Fermentation.
  • The example is yeast.
  • But in muscle tissue of animal (man) and in some bacteria, lactic acid is formed.
  • After excessive work, man is tired only due to the formation of lactic acid in the muscles.

Aerobic Respiration

  • It is a slow oxidation and involves 6 oxidation steps:
  • How Respiration?
    • Breakdown of glucose (i.e. release of H) through Glycolysis + Link + Krebs Cycle
    • Union of all Hydrogen (from Glucose) with atmospheric oxygen β†’ Through Electron Transport System (ETS)
  • Here Acetyle Co-enzyme A is formed which is the connecting link between glycolysis and Krebs cycle. Hence this stage is called link. There are three changes in the link -
  • Net result of the reaction:

    [Pyruvate + Coβ€”A + NAD+ β†’ Acetyl Coβ€”A + NADH2 + CO2] x 2 molecules

  • Release: 2CO2 (Two molecule of CO2) + 4H

III. Krebs cycle/Citric acid cycle/Tricarboxylic acid cycle

  • Name of scientists: Krab
  • First product of reaction: Citric Acid
  • Nature of organic acid produced in the reaction: Tricarboxlic Acid
  • Under aerobic conditions pyruvic acid is oxidized through a Tricarboxylic Acid Cycle given by Wood et al (1942) and Krebs (1943). Energy is released due to breaking of bond of carbon-carbon into CO2.

Difference between Calvin and Krebs Cycle

πŸ€— Conclusion: Both Calvin and Krebs Cycles are antiparallel reactions.

  • All reactions of Krebs cycle are reversible, but the reaction of link are not reversible.
  • No oxygen is taken up in the TCA cycle itself but is taken up in the respiratory chain.
  • Enzyme: Decarboxylase β†’ For removal of CO2 acts twice, specific action on
    • Oxalo Succinic Acid [Source of CO2 in K.C.]
    • Ξ±-Ketoglutamic Acid [Source of CO2 in K.C.]
  • Total no. of CO2 produced in K.C. from 2 molecule of Acetyl Co-A β†’ 4 CO2

πŸ‘‰πŸ» ATP production through K.C.

  • Breaking down of Succinyl Co-A
  • Releases chemical bond energy.
  • GDP + Pi β†’ GTP (Pi means inorganic phosphate)
  • GTP + ADP β†’ GDP + ATP
  • Since one molecule of ATP is produced from one molecule of Acetyl Co-A
  • Two molecule of Acetyl Co-A β†’ 2ATP

Phosphorylation

  • If the Light Energy then called Photophosphorylation. E.g. photosynthesis here process is transformation of energy.
  • If Chemical Bond Energy then called Trans/Substrate Phosphorylation. E.g. K.C. process is transfer of energy.
  • If Oxidation Energy then called Oxidative Phosphorylation. E.g. Electron Transport System (ETS)

Electron Transport System (ETS) / Respiratory Chain

  • Here oxidation of NADH + H+ and FADH + H+ occurs
    • Electron donor is Hydrogen
    • Electron carriers β€” Cytochrome (in F1 particle of Mitochondria)
    • Electron Acceptor β€” Oxygen (from atmosphere)
    • Production of H2O and ATP
  • NADH2 & FADH2 are the only temporary storage place for electrons.
  • Respiratory chain is the system of mitochondrial enzymes and electron carriers through which the re-oxidation of NADH to NAD+ under aerobic conditions by transfer of electrons from NADH to O2. Respiratory chain also transfer the electrons from succinic acid to O2.

πŸ‘‰πŸ» No. of released NADH2/FADH2:

πŸ‘‰πŸ» Released FADH2 molecule:

  • Only through K.C. = 1 x 2 = 2 FADH2
  • In the oxidation of one molecule of reduced NAD (i.e. NADH2) to NAD+, 3 molecules of ATP are released.
  • In the oxidation of one molecule of reduced FAD (i.e. FADH2) to FAD+ only 2 molecules of ATP are generated.
  • 2 molecules of FADH2 released 2 x 2 = 4 ATP
  • Total No. of ATP produced in ETS = 30 ATP
  • Total No. of ATP produced in Glycolysis = 4 ATP
  • Total No. of ATP produced = 34 ATP

πŸ‘‰πŸ» Energy released during respiration

  • On the basis of stages of respiration
    • Glycolysis = 2 ATP
    • Krebs cycle = 2 ATP
    • ETS = 34 ATP
    • Total ATP produced in respiration = 38 ATP ⭐️

πŸ‘‰πŸ» On the basis of site

  • Enzyme of glycolysis: On cytosol (cytoplasmic solution)
  • i.e. Outside Mitochondria : 2ATP
  • Enzyme of K.C.: On Perimitochondrial space (Matrix)
  • Enzyme of ETS: On cytochromes (Oxysomes/F1 Particles)
  • i.e. Inner membrane of Mitochondria thus
    • Within Mitochondria = 2 ATP of K.C.
    • 34 ATP of ETS
  • Total = 36 ATP

πŸ‘‰πŸ» On the basis of phosphorylation:

  • Oxidative phosphorylation = 34 ATP
  • Substrate/Trans phosphorylation = 4 ATP
  • i.e. Direct oxidation of substrate = 38 ATP
  • 2 ATP in glycolysis + 2ATP in K.C.

πŸ‘‰πŸ» On the basis of 3 stages excluding ETS

  • Glycolysis = 8 ATP (through respiratory chain) in presence of O2
  • Link = 6 ATP
  • K.C. = 24 ATP (6 NADH2 + 2FADH2 + 2GTP)
  • Total = 38 ATP

Formula of Respiration Reaction

Outputs

  • No. of CO2 molecule through
    • Link = 2
    • K.C. = 4
    • Total molecules released during respiration = 6 CO2
  • No. of H2O molecule through
    • ETS = (1 x 10) + (1 x 2) = 12 H2O
    • 10 means 10 molecules of NADH2
    • 2 means 2 molecules of FADH2
  • No. of net ATP produced = 38 ATP

Inputs

  • Glucose: C6H12O6

  • Oxygen: Β½ O2

  • Formula: After balancing the above inputs & outputs:

    C6H12O6 + 6O2 + 6H2O = 6CO2 + 12H2O + 38ATP

    C6H12O6 + 6O2 + 6H2O = 6CO2 + 12H2O + 686 KCal

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