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7.2. Catabolism

Catabolism

The catabolism is the part of metabolism consisting of the transformation of complex biomolecules in simple molecules and storing the chemical energy obtained in the form of high energy bonds in molecules adenosine triphosphate (ATP). NADPH is also generated, with reducing power, which the cell will use in anabolic processes.

This energy can be used in the endergonic reactions of anabolism, so catabolism and anabolism are connected.

Catabolic reactions take place in all organisms, be they autotrophic or heterotrophic, and are very similar in all of them.

The catabolism, depending on the nature of the molecule that is reduced by accepting electrons, can be:

  • Fermentation: the molecule that is reduced is an organic compound. Generally, pyruvate accepts electrons, reducing itself, originating organic compounds such as ethanol  or lactic acid . It only produces ATP by phosphorylation at the substrate level.
  • Respiration: the molecule that is reduced is inorganic. It distinguishes:
    • Aerobic respiration: the molecule that is reduced is oxygen, producing water. ATP is produced by phosphorylation at the substrate level and by oxidative phosphorylation. It is the most common and most efficient type of metabolism.
    • Anaerobic respiration: if the substance that is reduced is not oxygen, but NO3- , SO42- , ... It produces ATP both at the substrate level and by oxidative phosphorylation. It only occurs in some types of bacteria.

Types of catabolism according to the final electron acceptor.

Stages of carbohydrate respiration (the 2nd and 3rd do not occur in fermentations).

Types of catabolism according to the nature of the molecule that is oxidized.

 

 

Catabolism

 

Breathing

 

 

Aerobic

 

Anaerobic

Stages

1st. Glycolysis

2nd. Krebs cycle

3rd. Respiratory chain

 

Types of Catabolism

Catabolism of carbohydrates

Lipid catabolism

Protid catabolism

Catabolism of nitrogenous bases

Fermentation

1st. Glycolysis

Fundamental ideas about catabolism

Catabolism

  • The  catabolism  is the part of metabolism consisting of the transformation of complex biomolecules in simple molecules and storing the chemical energy obtained in the form of high energy bonds in molecules  adenosine triphosphate  (ATP). NADPH is also generated, with reducing power, which the cell will use in anabolic processes.
  • Depending on the molecule that is reduced, which captures the electrons, there are two types of catabolism:
    • Fermentation: the molecule that is reduced is an organic compound. It is carried out in microorganisms such as yeast and fungi and in the muscle tissue of animals.
    • Respiration: the molecule that is reduced is inorganic. It distinguishes:
      • Aerobic respiration: the molecule that is reduced is oxygen, producing water. 
      • Anaerobic respiration: if the substance that is reduced is not oxygen, but NO3- , SO42- , ...