13. Respiration and Energy Transfer - part 02 - Anaerobic respiration

 

13. Respiration and Energy Transfer - part 02 - Anaerobic respiration


Anaerobic respiration :

  • Anaerobic respiration is the cellular respiration that does not involve the oxygen at all. It is also called as fermentation. 
  • It is completed through steps like 
  1. glycolysis and 
  2. conversion of glycolytic product to any suitable product like lactic acid, ethanol, etc.

Glycolysis :


  • Glycolysis involves the breakdown of glucose molecule into two pyruvic acid molecules. Hence known as glycolysis. 
  • This is a common step in anaerobic as well as aerobic respiration.
  • It occurs in cytoplasm of cell. It is completed in two phases as preparatory phase and pay-off phase.
  • Overall process of glycolysis is completed through ten steps. 
1. preparatory phase :
  • First five steps constitute the preparatory phase through which glucose is phosphorylated twice at the cost of two ATP molecules and a molecule of fructose 1, 6-bisphosphate is formed.
  • This molecule is split to form a molecule of glyceraldehyde 3-phosphate and a molecule of dihydroxyacetone phosphate. 
  • Both of these molecules are 3-carbon carbohydrates (trioses) and are isomers of each other. 
  • Dihydroxy acetone phosphate is isomerised to second molecule of glyceraldehyde-3-phosphate.
  • Thus, two molecules of glyceraldehyde-3- phosphate are formed and here, first phase i.e. preparatory phase of glycolysis ends.
2. pay-off phase :
  • In the pay-off phase, both molecules of glyceraldehyde-3-phosphate are converted to two molecules of 1, 3-bisphoglycerate by oxidation and phosphorylation. 
  • Here, phosphorylation is brought about with the help of inorganic phosphate and not ATP.
  • Both molecules of 1, 3-bisphosphoglycerate are converted into two molecules of pyruvic acid through series of reactions accompanied with release of energy.
  • This released energy is used to produce ATP (4 molecules) by substrate-level phosphorylation.



do you know ?
1. Glycolysis

  • It is only source of energy production in 
  1. erythrocytes
  2. renal medulla
  3. brain and 
  4. sperm.

2. Some plant tissues which are modified to store starch (like potato) mainly depend upon glycolysis for energy production.

3. myoglobin of skeletal muscles is oxygen storing and transporting pigment .

  • Red (dark) muscles are richer in myoglobin than the white (pale) muscles. 
  • Therefore, red fibers can utilize the oxygen stored in myoglobin to continue energy production over prolonged period by aerobic oxidation of glucose. 
  • This enables them to perform sustained work over a long period. 
  • On the contrary, white fibers produce the energy needed for very fast and severe work by glycolysis as sufficient oxygen is not immediately available to them for such work. 
  • But white muscles accumulate lactic acid and get fatigued in a short time. 
  • Thus athletes with a higher proportion of red fibers in their muscles are physiologically better adapted for sustained events like marathon or swimming over long distances.



    Anaerobic respiration in muscle :

    • In muscles, the NADH+H+ produced during glycolysis is reoxidized to NAD+ by donating one proton and two electrons to pyruvic acid which yields lactic acid. 
    • Skeletal muscles usually derive their energy by anaerobic respiration. 
    • After vigorous exercise lactic acid accumulates, leading to muscle fatigue. 
    • During rest, however, the lactic acid is reconverted to pyruvic acid and is channeled back into the aerobic respiration pathway.



      Anaerobic respiration in yeast :
      • In yeast, the pyruvate is decarboxylated to acetaldehyde. 
      • The acetaldehyde is then reduced by NADH+H+ to ethanol. Carbon dioxide is also produced in this process.
      • This type of anaerobic respiration is termed alcoholic fermentation. 
      • Accumulation of ethanol by fermentation in a culture of yeast may stop further multiplication and lead to the death of cells.
      • In the presence of oxygen however, yeast can respire aerobically.

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