Amino Acid Structure and Peptide Formation

Amino Acids Classification

• Dicarboxylic amino acids: Aspartic acid (Asp, D) and Glutamic acid (Glu, E)
• Amino acids with amide group: Asparagine (Asn, N) and Glutamine (Gln, Q)
• Dibasic amino acids: Lysine (Lys, K) and Arginine (Arg, R)
• Heterocyclic amino acid: Histidine (His, H)
• Imino acid: Proline (Pro, P) - also known as Imino acid due to its Pyrrolidine ring structure

Aromatic Amino Acids

• Phenylalanine (Phe, F)
• Tyrosine (Tyr, Y)
• Tryptophan (Try, W)

Structure of Amino Acids

• Each amino acid has a core structure consisting of a central carbon atom known as the alpha (α) carbon
• Amino acids contain an amino group, a carboxylic group, and a side chain

Formation of Peptide Linkage

• Dipeptide: 2 amino acids linked together
• Tripeptide: 3 amino acids linked together - can have 20^3 = 8000 different combinations
• Tetrapeptide: 4 amino acids linked together
• Oligopeptide: 5-9 amino acids linked together
• Polypeptide: 10-50 amino acids linked together
• Polypeptides with more than 50 amino acids are usually termed as proteins

Simple and Branched-Chain Amino Acids

• Simple amino acids: Glycine (Gly, G), Alanine (Ala, A)
• Branched-chain amino acids: Valine (Val, V), Leucine (Leu, L), Isoleucine (Ile, I)

Hydroxy and Sulfur-Containing Amino Acids

• Hydroxy amino acids: Serine (Ser, S), Threonine (Thr, T)
• Sulfur-containing amino acids: Cysteine (Cys, C), Methionine (Met, M)