Amino acids are the building blocks of proteins. They have properties suited for various biological functions including the ability to polymerize into proteins. There are 20 standard amino acids that vary in properties like size, charge, and hydrophobicity. Amino acids polymerize via peptide bonds to form polypeptide chains that fold into complex protein structures. The sequence and properties of amino acids in the chain determine the structure and function of each protein.

1. Amino acids
PRESENTED BY :-
MR. ROMAN BAJRANG
BASIC BS.C NURSING 2ND YEAR
RELIANCE INSTITUTE OF NURSING

2. Amino Acids: Building Blocks of Protein
1. Proteins are heteropolymers of -amino acids
2. Amino acids have properties that are well suited to carry out a
variety of biological functions
Functions:
1. Capacity to polymerize
2. Useful acid-base properties
3. Varied physical properties
4. Varied chemical functionalities

3. Edited by :- MR. ROMAN BAJRANG

4. Most -Amino Acids are Chiral
 The -carbon has always four
substituents and is tetrahedral
 All (except proline) have an
acidic carboxyl group, a basic
amino group, and an alpha
hydrogen connected to the -
carbon
 Each amino acid has an
unique fourth substituent R
 In glycine, the fourth
substituent is also hydrogen
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Edited by :- MR. ROMAN BAJRANG

5. Amino Acid Enantiomers
•Steroisomers / enantiomers
•Biological system only synthesize
and use L-amino-acids
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Edited by :- MR. ROMAN BAJRANG

6. Amino Acid Classification
• Aliphatic
• Aromatic
• Sulfur containing
• Polar/uncharged
• basic/acidic
Hydrophobic
Hydrophilic
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Edited by :- MR. ROMAN BAJRANG

7. AminoAcidTypes
Name R-Group Properties
Glycine G Gly Hydrophobic
Alanine A Ala Hydrophobic
Valine V Val Hydrophobic
Leucine L Leu Hydrophobic
Isoleucine I Ile Hydrophobic, two chiral carbons
Proline P Pro Cyclic, not terribly hydrophobic
Phenylalanine F Phe Hydrophobic, bulky
Tyrosine Y Tyr Less hydrophobic (than Phe), bulky
Tryptophan W Trp Hydrophobic, bulky (indole ring)
Cysteine C Cys Hydrophobic, highly reactive (S-S link)
Methionine M Met Hydrophobic (start a.a.)
Serine S Ser Hydrophilic, reactive
Threonine T Thr Hydrophilic, reactive, two chiral carbons
Lysine K Lys Highly hydrophilic, positively charged
Arginine R Arg Highly hydrophilic, positively charged
Histidine H His Highly hydrophilic, positive or neutral
Aspartate D Asp Highly hydrophilic, negatively charged
Glutamate E Glu Highly hydrophilic, negatively charged
Asparagine N Asn Uncharged
Glutamine Q Gln Uncharged 7

8. Aliphatic (alkane) Amino Acids
Hydrophobicity
•Proline (pro, P)- cyclic “imino acid”
•Glycine(gly, G)-only non-chiral amino acid, not hydrophobic
•Alanine (ala, A) – R-group = methyl-group
•Valine (Val, V) –
•Leucine (Leu, L) –
•Isoleucine (Ile, I) -2 chiral carbons
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9. Aromatic Amino Acids
• All are hydrophobic
• All contain aromatic group
• Absorb UV at 280 nm
• Phenylalanine (Phe, F)
• Tyrosine (Tyr, Y) – -OH ionizable (pKa = 10.5), H-Bonding
• Tryptophan (Trp, W) – bicyclic indole ring, H-Bonding
Phe Tyr
TRP
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10. Sulfur Containing Amino Acids
• Methionine (Met, M) – “start” amino
acid, very hydrophobic
• Cysteine (Cys, C) – sulfur in form of
sulfhydryl, important in disulfide
linkages, weak acid, can form
hydrogen bonds.
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Edited by :- MR. ROMAN BAJRANG

11. • Contain carboxyl groups (weaker acids than a-carboxyl-group)
• Negatively charged at physiological pH, present as conjugate
bases (therefore –ate not –ic acids)
• Carboxyl groups function as nucleophiles in some enzymatic
reactions
• Aspartate –
• Glutamate –
Acidic Amino Acids
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12. Basic Amino Acids
• Hydrophillic nitrogenous bases
• Positively charged at physiological pH
• Histidine – imidazole ring protonated/ionized, only amino acid
that functions as buffer in physiological pH range.
• Lysine - diamino acid, protonated at pH 7.0
• Arginine - guianidinium ion always protonated, most basic amino
acid
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Histidine
Lysine Arginine
Edited by :- MR. ROMAN BAJRANG

13. • Polar side groups, hydrophillic in nature, can form hydrogen bonds
• Hydroxyls of Ser and Thr weakly ionizable
• Serine (Ser, S) – looks likeAla
• Threonine (Thr, T) – 2 chiral carbons
• Asparagine (Asn, N) – amide of aspartic acid
• Glutamine (Gln, Q) – amide of glutamic acid
Polar Uncharged Amino Acids
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Edited by :- MR. ROMAN BAJRANG

14. Essential/Non-Essential Amino Acids
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17. Peptides and Peptide bonds
 Peptide bond in a
di-peptide
 “Peptides” are
small
condensation
products of amino
acids
 They are “small”
compared to
proteins (di, tri,
tetra… oligo-)
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18. Peptide Ends are Not the Same
Numbering starts from the amino terminus
AA1 AA2 AA3 AA4 AA5
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19. 19
ProteinPrimaryStructure
Note the
Polarity of
the
sequence
(amino 
carboxy)
Note also the disulfide
linkages (cys-cys  S-S
bonds; actually considered
a component of tertiary
structure)
Edited by :- MR. ROMAN BAJRANG

20. Proteins are:
• Polypeptides (covalently linked -amino acids) + possibly –
• cofactors,
• coenzymes,
• prosthetic groups,
• other modifications
• Cofactor is a general term for functional non-amino acidcomponent
– Metal ions or organic molecules
• Coenzyme is used to designate an organiccofactors
– NAD+ in lactate dehydrogenase
• Prosthetic groups are covalently attachedcofactors
– Heme in myoglobin
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Edited by :- MR. ROMAN BAJRANG

21. Protein Nomenclature
• Peptides 2 – 50 amino acids
• Proteins >50 amino acids
• Amino acid with free -amino group is the
amino-terminal or N-terminal residue
• Amino acid with free -carboxyl group is the
carboxyl-terminal or C-terminal residue
• Three letter code – Met-Gly-Glu-Thr-Arg-His
• Single letter code – M-G-E-T-R-H
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Edited by :- MR. ROMAN BAJRANG

22. FiveCategories
Note 20
(naturally
translated)
amino acids
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