Overview of metabolism

Overview of metabolism

A) Metabolism:

Metabolism is the set of chemical reactions that happen in living organisms to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments.

B) Types of Metabolic processes:

==> Metabolism starts by the digestion of nutrients obtained from the diet where:-

  • The complex molecules of carbohydrates, proteins and lipids obtained from the diet are converted into simple molecules (glucose, amino acid and fatty acids respectively) then absorbed in the intestine from which the simple molecules move through the hepatic portal vein to the liver which is the factory responsible for more than 90% of the metabolic processes.

==> The metabolism is classified into two process:

1) Catabolism:

It is the breakdown of the complex molecules into small molecules to produce the energy which stored in ATP molecule (Adenosine Tri-Phosphate called the bank of energy) and required for life and cell reproduction.

2) Anabolism:

It is the process of building up complex molecules – required for normal life and health – from the simple molecules using the stored energy resulting from the catabolism process.

–  For Example: The regeneration of dead cells is a dynamic process (i.e. involve movement) which means that it requires energy thus the nutrients is the fuel of the human body.

C) Properties of metabolism:

1) Integrated:

Where the carbohydrates, proteins and lipids participates in the energy production (Complementary in ) whatever the place of the metabolic process in the cell where

  •  They are converted into simple molecules where:

Fats → fatty acids

Proteins → amino acids

Carbohydrate → glucose + (galactose + fructose)

      ↓                     ↓

glucose            glucose

and then all the simple molecules enter the same cycle which known as kerb’s cycle.

  • Some of these metabolic processes occur in cytoplasm and others occur in mitochondria according to the enzymes used by the metabolic process.


Glycolysis, which is the oxidation of glucose, occurs in cytoplasm because the enzymes used in it are present in cytoplasm.

In other words, the metabolism is integrated process because the net result of the breakdown of the carbohydrate, protein and lipid is the production of energy.

2) Regulated:

Where the cell has the enzymes which represent the controlling mechanisms which organize the metabolic processes in order to use the optimum benefits from the energy where if the metabolic processes aren’t controlled the energy will be dispersed without any benefits.

Remember the Mechanism of controlling enzymes:

The feedback mechanism:

Which is the control of the activity of the enzymes by inhibition or activation of them according to the need for the enzyme

The allosteric control:

  1. In which certain molecules bind to certain chemical groups at a certain area on the surface of the enzyme, called the “allosteric site”, resulting in conformational changes that lead to changes in the arrangement of the chemical groups of that enzyme at the catalytic site.

  2. It is a type of feedback inhibition

You can follow other topics and lectures about metabolism from the menu … Medicine>>biochemistry>>metabolism


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