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13. Respiration and Energy Transfer

-Created By-

Shri. Deshmukh A. B.

Asst. Teacher,

Agasti Arts, Commerce & Dadasaheb Rupwate Science College, Akole

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Can you recall?

  • 1. Which nutrients are used for energy production?
  • 2. Which is most preferred nutrient among carbohydrate, protein and fat for energy production? Why?
  • 3. Why do organisms take up oxygen and release carbon dioxide?
  • 4. What is aerobic and anaerobic respiration?
  • 5. Which steps are involved in aerobic respiration?

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Always Remember

  • 1. Maintenance of life requires continuous supply of energy.
  • 2. Respiration fulfils the continuous need of energy.

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13.1 Formation of ATP :

  • Formation of ATP is called as phosphorylation.
  • In nature, phosphorylation occurs in three different ways as –
    • photophosphorylation,
    • substrate level phosphorylation and
    • oxidative phosphorylation.
  • Photophosphorylation is synthesis of ATP by addition of inorganic phosphate to ADP in presence of light .
  • Substrate-level phosphorylation is a direct phosphorylation of ADP by transfer of a phosphate group from any suitable substrate.
    • It occurs in cytoplasm of the cells and matrix of mitochondria.

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  • Oxidative phosphorylation:
    • It is phosphorylation of ADP at the cost of energy released during oxidation of substrates like NADH+H+ and FADH2 .
    • This occurs on the inner mitochondrial membrane only.
  • When energy is required for any metabolic process, ATP is hydrolysed.
  • ATP hydrolysis releases the energy which is used for the metabolic activities.

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  • Respiration is a catabolic process wherein complex organic substrate is oxidized to simple components to generate biological energy.
  • Cellular respiration occurs in two different ways as
    • Anaerobic respiration
    • Aerobic respiration.

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13.2 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
    • Glycolysis and
    • Conversion of glycolytic product to any suitable product like lactic acid, ethanol, etc.

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Glycolysis :

  • This 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
    • Pay-off phase.

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  • Overall process of glycolysis is completed through ten steps.
  • First five steps constitute the preparatory phase.
  • 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 (3PGAL)
    • A molecule of dihydroxyacetone phosphate (DHAP)
  • Both of these molecules are 3-carbon carbohydrates (trioses) and are isomers of each other.
  • DHAP is isomerised to second molecule of 3PGAL.
  • Thus, two molecules of glyceraldehyde-3- phosphate are formed and here, first phase i.e. preparatory phase of glycolysis ends.

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  • 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.
  • Overall reaction of glycolysis:
    • Glucose + 2ATP + 2iP + 4ADP + 2NAD+ -----------------> 2Pyruvate + 2ADP + 4ATP + 2NADH+H+ +2H2O

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  • 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.

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  • 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.

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  • 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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  • Glycolysis is under tight control.
  • Its rate depends upon the requirement of ATP and many other factors.
  • Glycolytic rate control is achieved by complex interplay between ATP consumption, NADH2 regeneration and regulation of various glycolytic enzymes like hexokinase, PFK-1, pyruvate kinase, etc.
  • Besides, it is also controlled by hormones like glucagon, epinephrine and insulin.

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Use your brain power:

  • 1. What is role of Mg++, Zn++ in various steps of glycolysis?
  • 2. Why some reactions of glycolysis are reversible and some irreversible?
  • 3. Why is glycolysis considered as biochemical proof of evolution?
  • 4. Why do athletes like sprinters have higher proportion of white muscle fibers?

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Do you know?

  • 1. Glycolysis is only source of energy production in erythrocytes, renal medulla, brain and sperm.
  • 2. Some plant tissues which are modified to store starch (like potato) mainly depend upon glycolysis for energy production.
  • 3. In chapter 3, Biomolecules, you have read about the oxygen storing and transporting pigment myoglobin of skeletal muscles.
    • Red (dark) muscles are richer in myoglobin than the white (pale) muscles.

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  • 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.