There are about 300 amino acids that occur in nature, with 20 common ones found in proteins. Amino acids can be classified based on their structure, polarity, and whether they are aromatic, heterocyclic, or aliphatic. Some amino acids like valine, isoleucine, and leucine are branched, while others are non-branched. Amino acids can also be classified based on their nutritional or metabolic properties. Cystine forms disulfide bonds between two cysteine amino acids in proteins. Selenocysteine is considered the 21st amino acid and contains selenium instead of sulfur. Some D-amino acids also occur naturally, like D-serine and D-aspartate in brain

1. Amino acids & Peptides
By Dr M.H.Abdelzaher

2. Amino Acids
Structure:
There are about 300 amino acids occurring in
nature. Only 20 of them occur in proteins

4. Characters of Amino Acids

7. According to fatty acids they derived from

15. According to polarity of the R group

18. According to if the amino acid aromatic, heterocyclic or
aliphatic

19. Branched and Non branched AA
Branched AA: include Valine, Isoleucine and
Leucine
Non branched AA: Other AA

21. Nutritional classification of AA

23. Metabolic Classification

26. Amino acids found in proteins and formed by post translational modifications

27. Biomedical Importance of AA

28. Note:
Cystine: is a dicysteine
In proteins, the -SH groups of two cysteines can become
oxidized to form a dimer cystine, which contains a covalent
cross-link called a disulfide bond (-S-S-).
Selenocysteine: Selenocysteine is an L-α-amino acid found in
proteins Humans contain approximately two dozen
selenoproteins that include certain peroxidases and
reductases, which circulates in the plasma, and the
iodothyronine deiodinases responsible for converting
thyroxine (T4) to the thyroid hormone 3,3'5-triiodothyronine
(T3)

29. A selenium atom replaces the sulfur of its elemental
analog, cysteine.
Selenocysteine is not the product of a posttranslational
modification, but is inserted directly into a growing
polypeptide during translation. Selenocysteine thus is
commonly termed the “21st amino acid.”
Unusual tRNA called tRNASec which utilizes the UGA
anticodon that normally signals STOP. However, the
protein synthetic apparatus can identify a
selenocysteine-specific UGA codon by the presence of
an accompanying stem-loop structure, called the
selenocysteine insertion element, in the untranslated
region of the mRNA

30. D-Amino Acids
D-Amino acids that occur naturally include free
D-serine and D-aspartate in brain tissue, D-
alanine and D-glutamate in the cell walls of
gram-positive bacteria, and D-amino acids in
certain peptides and antibiotics produced by
bacteria and fungi

32. Physical properties

36. Chemical properties

38. Peptides

39. Peptide bond

41. Biologically active peptides