The human body is constituted in about 20% by protein. Proteins, on their hand, are constituted by amino acids. Therefore, the intake of proteic food is very important so that the proteins of such foods may be metabolized and the amino acids and energy gathered to maintain the body’s protein levels.
The existence of correct amounts of amino acids in the body is essential for several functions:
- the body’s skeletal muscle constitution;
- for transport of nutrients to the same cells;
- cell repair;
- cell communication:
- influence on organs’ good function;
- eliminating residues from metabolism;
- amino acids are also nutrients in itself, many of them essential for the human body;
- serve as substrates in biological synthesis processes;
- base for nucleotides (DNA), hormones and neurotransmitters;
- control of cell process.
Some amino acids are synthetized by the body; others, the essential ones, need to be provided in the diet and then take more complex pathways to be synthetized. Synthesis of amino acids can be achieved through:
- Glycolytic intermediates, in which, since not all carbon is transformed into pyruvate, they are used for the citric acid (or Krebs) cycle;
- Krebs cycle intermediates, by producing amino acids with precursor activity;
- Penthose phosphate pathway, in which the production of erythrose-4-phosphate is used for synthesis of aromatic amino acids;
Amino acids are, primarily, the unit (monomer) of a protein (macromolecule). So, the groups of amino acids that constitute a protein will give it specific characteristics, such as folding and stability, and function.
The proteins, themselves, and amino acids, can also be used for energy production.
The process through which there is degradation of proteins is called proteolysis, or protein catabolism. Further ahead, the remaining amino acids can also suffer degradation into their primary constituents. The resulting amino acids, from protein breakage, can be transported to the interior of cells, in which they will be used to synthetize other proteins, by the use of RNA and ribosomes.
On the other hand, the amino acids of protein can, alternatively to carbon hydrates, be used to produce energy.
Since ATP (energy) is produced by sugars degradation, there is the need to convert the amino acids into molecules that are identifiable as such. In order for that to happen, the nitrogen must then be removed, by a process called deamination (removal of the NH2 group), which produces ammonia. This ammonia will be posteriorly removed from the system in the form of urea (conversion made in the liver).
With nitrogen removed, only carbon, oxygen and hydrogen remains, the basic constituents of a sugar; so, the amino acid that went through deamination is now called a keto acid. The keto acids that resulted from the amino acids deamination can now be turned into acetyl sugar, by a process called gluconeogenesis, promoted by the hormone insulin.
The acetyl sugars enter now the Krebs cycle, where they are broken into simple molecules of carbon dioxide and hydrogen. The hydrogen is then collected by FAD+ and NAD+. Along with this process of transferring hydrogen to these molecules, there is phosphorylation, in which a phosphate group gets attached to ADP, resulting in formation of energy molecules, the ATP that cells then use.
Antranik (2012, March 18). Retrieved from http://antranik.org/the-catabolism-of-fats-and-proteins-for-energy/
Gutiérrez-Preciado, Ana, Romero, Hector, Peimbert, Mariana (2010). Retrieved from http://www.nature.com/scitable/topicpage/an-evolutionary-perspective-on-amino-acids-14568445