Human Biochemistry, Volume 1 - Murray R. 1993

Metabolism of Proteins and Amino Acids
Biosynthesis of Amino Acids
Introduction

When evaluating the Nutritional Value of Amino Acids, we often refer to some of them as "essential" and others as "nonessential" (Table 29.1). Although this is entirely correct from a nutritional standpoint, one should not lose sight of the overall biological significance and indispensability of all 20 amino acids. Furthermore, it could even be argued that "nonessential" Amino acids are actually more critical to The Cell than essential ones, since the evolutionary loss of an Organism's (e.g., human) ability to synthesize Certain amino acids appears far more natural in the case of less vital ones.

Nutritional requirements for specific compounds indicate that relying on an external source of metabolites can sometimes be more advantageous for an organism's survival than synthesizing them internally. If a specific intermediate is readily available in the diet, an organism that retains The ability to synthesize this compound passes on corresponding Genetic information of negative value to future generations. This trait is not merely useless to the organism; it is actively detrimental, as it needlessly expends nutrients and ATP on the synthesis of "redundant" DNA segments. In Prokaryotic Cells, the number of Enzymes required to synthesize Essential Amino Acids significantly exceeds the number required for nonessential amino acids (Table 29.2). Consequently, retaining the ability to synthesize "easy" amino acids while losing the capacity to synthesize "difficult" ones offers distinct biological advantages.

Class="center">Table 29.1. Human amino acid requirements

Essential

Nonessential

Arginine 1)

Alanine

Valine

Asparagine

Histidine 1)

Aspartate

Isoleucine

Hydroxylysine 2)

Leucine

Hydroxyproline 2)

Lysine

Glycine

Methionine

Glutamate

Threonine

Glutamine

Tryptophan

Proline

Phenylalanine

Serine

Tyrosine

Cysteine

1) Strictly speaking, this is a "semi-essential" amino acid because it is synthesized in the body, but The rate of synthesis is insufficient to support growth during childhood.

2) Not utilized in Protein Synthesis; instead, it is formed during the post-translational Processing of Collagen.

Table 29.2. Enzymes required for the synthesis of amino acids from amphibolic metabolites

Number of enzymes required for the synthesis of

essential amino acids

nonessential amino acids

Arg 7 (from Glu)

Ala 1

His 6

Asp 1

Thr 6

Asn 1 (from Asp)

Met 5

Glu 1

Lys 8

Gln 1 (from Glu)

Ile 8

Pro 3 (from Glu)

Val 1

Ser 3

Leu 3

Gly 1 (from Ser)

Phe 10

Cys 2 (from Ser + S2-)

Trp 5

Tyr 1 (from Phe)

Hyl 1 (from Lys)

Total 59

Hyp 1 (from Pro)

Total 17


Last update: 06/08/2026

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