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Glycine and valine are amino acids and when connected, the bond connecting them is called a peptide bond. Amino acids are so called because of the presence of a carboxylic acid group, COOH, and an amine group, NH2. Each amino acid is distinguished by the side chains attached to them. (I have included the structures of glycine, valine, and the glycine-valine dipeptide. As you can see, glycine has H as a side chain, while valine has a more complicated group, CH(CH3)CH3.) The peptide bond connects amino acids together via the carboxylic acid group of one, and the amine group of the other. Formation of a peptide bond is a type of a condensation reaction, one which produces water as a by-product.
Below is a simplified reaction of two amino acids with side chains R1 and R2:
H2N-CHR1-COOH + H2N-CHR2-COOH
R1 can be H if the first amino acid is glycine, and R2 is CH(CH3)CH3 if the second is valine. The peptide bond forms via condensation of the two amino acids, where water is formed from the OH group of the first amino acid and an H from the amine group of the second:
H2N-CHR1-CO-HN-CHR2-COOH (first amino acid in bold)
As can be seen in this simplified reaction and the attached image, the peptide bond is formed between the carbon of the carboxylic acid of amino acid 1 and the nitrogen of the amine group of amino acid 2.
Functional groups present are, as already mentioned, carboxylic group (COOH) and amine group (NH2) from the amino acids. The resulting molecule from the formation of the peptide bond is an amide (RC(=O)NR, see attachment for other forms of amides).
By convention, polypeptides are written and drawn from the N-terminal (amine group of first amino acid) to the C-terminal (carboxylic group of the last amino acid).
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