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A rare exception to the dominance of α-amino acids in biology is the β-amino acid beta alanine (3-aminopropanoic acid), which is used in plants and microorganisms in the synthesis of pantothenic acid (vitamin B 5), a component of coenzyme A. [83]
Amino acids that must be obtained from the diet are called essential amino acids. Eukaryotes can synthesize some of the amino acids from other substrates . Consequently, only a subset of the amino acids used in protein synthesis are essential nutrients .
The side chains of the standard amino acids, detailed in the list of standard amino acids, have a great variety of chemical structures and properties; it is the combined effect of all of the amino acid side chains in a protein that ultimately determines its three-dimensional structure and its chemical reactivity. [29]
Amino acids that have been incorporated into peptides are termed residues. A water molecule is released during formation of each amide bond. [ 6 ] All peptides except cyclic peptides have an N-terminal (amine group) and C-terminal (carboxyl group) residue at the end of the peptide (as shown for the tetrapeptide in the image).
Modified amino acids are sometimes observed in proteins; this is usually the result of enzymatic modification after translation (protein synthesis). For example, phosphorylation of serine by kinases and dephosphorylation by phosphatases is an important control mechanism in the cell cycle .
Alanine is the simplest α-amino acid after glycine. The methyl side-chain of alanine is non-reactive and is therefore hardly ever directly involved in protein function. [12] Alanine is a nonessential amino acid, meaning it can be manufactured by the human body, and does not need to be obtained through the diet. Alanine is found in a wide ...
Proteins are made from amino acids. In humans, some amino acids can be synthesized using already existing intermediates. These amino acids are known as non-essential amino acids. Essential amino acids require intermediates not present in the human body. These intermediates must be ingested, mostly from eating other organisms. [6]
Strong mineral acids can readily hydrolyse the peptide bonds in a protein (acid hydrolysis). The standard way to hydrolyze a protein or peptide into its constituent amino acids for analysis is to heat it to 105 °C for around 24 hours in 6M hydrochloric acid. [27] However, some proteins are resistant to acid hydrolysis.