Proteins are composed of amino acids, which are the basic structural units. There are 20 amino acids that make up mammalian proteins. Amino acids contain an amino group, a carboxyl group, a hydrogen atom, and a distinctive side chain. They can be classified based on properties like charge, polarity, and nutritional properties. Amino acids join together via peptide bonds to form polypeptides and proteins. Dietary proteins are broken down into amino acids through digestion before being used for various metabolic functions in the body.

1. AMINO ACIDS & PEPTIDES
Dr. Neelam H. Zaidi
Neelamz@unifiji.ac.fj

2. • Proteins are the most
abundant and functionally
diverse molecules in living
systems.
• Proteins all share the
common structural feature
of being linear polymers of
amino acids.
Introduction

3. Introduction
• Approximately 300 amino acids present in nature.
• Only 20 amino acids are coded by DNA to appear in
proteins, they are also constituents of mammalian
proteins.
• Amino acids are the basic structural units of
proteins.

4. Definition
• Consists of an amino group
(-NH2), a carboxyl (-COOH)
group, a hydrogen (H) atom
and a variable/distinctive (R) group.
• All are attached (bonded) to a central α carbon atom.
• Free amino acids are found in blood and cells of
humans.

5. 20 AMINO
ACIDS
(R group)

6. Ionic Property of Amino Acids
• In physiologic pH (7.4), both –NH2 and –COOH are
ionized resulting the charged form of an amino
acids called zwitterion (dipolar ion)
• The amino group is protonated (-NH3
+) and the
carboxyl group is dissociated (deprotonated) (-COO- )
leading to a net charge zero.

7. Abbreviations & Symbols
• Each amino acid name
has an associated
three-letter abbreviation
and a one-letter symbol.

8. Classification
• L-amino acids are the building blocks of proteins.
• In proteins, almost all the carboxyl and amino
groups are combined, so side chains determine
the properties of proteins.
• The classification of amino acids are based on
properties of side chains.

9. • According to the charge and polarity of side chains at
acidic pH
 Amino acids with nonpolar side chains
 Amino acids with uncharged polar side chains
 Amino acids with acidic side chains
 Amino acids with basic side chains
Classification

10. http://www.people.virginia.edu/~rjh9u/aminacid.html
20 Amino Acids
Nonpolar,
hydrophobic
Polar, uncharged
Polar, charged

11. Biological or Physiological Classification
• The nutritional property of amino acids
 Essential Amino Acids
 Non-Essential Amino Acids
 Semi-Essential Amino Acids

12. Essential Amino Acids
• CANNOT be synthesized in the body.
• MUST be provided in the diet to
meet metabolic needs.
• Eight of the amino acids:
Isoleucine,Leucine,Lysine,Methionine,
Phenylaline,Threonine,Tryptophan,Valine,
Histidine.

13. Non-Essential Amino Acids
• Not necessarily be provided through diet.
• Can be biosynthesized in adequate amounts.
• Ten amino acids:
Alanine,Asparagine,Aspartic Acid,Arginine,
Glutamic Acid,Glutamine,Glycine,Proline,
Serine,Tyrosine

14. • Can be synthesized in the body
• NOT in sufficient amounts (during growth, repair and
pregnancy)
• Should be provided in the diet
• Two Amino Acids: Cysteine and Tyrosine
Semi-Essential Amino Acids

15. Metabolic Classification
• The fate of each amino acid:
 Glucogenic Amino Acids
 Ketogenic Amino Acids
 Ketogenic and Glucogenic Amino Acids

16. Glucogenic Amino Acids
• Potentially be converted to glucose
• The carbon skeleton of these amino acids gets
degraded to pyrurate, α-ketoglutarate, succinyl CoA,
fumarate and oxaloacetate and then converted to
glucose and glycogen.
• Such as: Alanine, Cysteine, Glycine, Arginine,
Glutamine, Isoleucine, Tyrosine etc.

17. Ketogenic Amino Acids
• potentially be converted to ketone bodies
• The carbon skeleton of these amino acids gets
degraded to acetyl CoA and acetoacetyl CoA. Then
converted to acetone, and β-hydroxybutyrate which
are the main ketone bodies. .
• Such as: Phenylalanine, Tyrosine, Tryptophan,
Isoleucine, Leucine, and Lysine
untreated diabetes mellitus

18. Ketogenic and Glucogenic Amino Acids
• Potentially be converted to to both glucose&ketone
bodies
• Can be converted to all the intermediates that are
required by glucose and ketone bodies synthesis.
• Such as: Tryptophan, Phenylalanine, Tyrosine and
Isoleucine.

20. Peptide Bond
• AA in proteins are joined together by peptide bonds.
• Amide linkages between the ɑ-carboxyl group of one
amino acid and the ɑ-amino group of another.
• A molecule of water is eliminated
Condensation
Dehydration

21. Overview

22. Digestion of Proteins
• Gradual breakdown of polypeptide by enzymatic
hydrolysis into amino acid molecules.
• Food: egg, milk, meat, cereals, nuts etc.*
• The end products of digestion are free amino acids,
di/tripeptides.
• Digestion:
Gastric digestion
Pancreatic digestion
Intestinal digestion

23. NUTRITIONAL
VALUE
 Legumes poor in Trp, but rich in Lys; Cereals
poor in Lys, but rich in Trp
 Mutual complementation of amino acids
 Protein deficiency-kwashiorkor, generalized
edema and liver enlargement, abdomen bulged
 Suggestion:the combined-action of protein
in diet

24. Digestion
And amino acids

26. Summary

28. References
• David L. Nelson (University of Wisconsin-Madison) , Michael M. Cox
(University of Wisconsin-Madison) : Lehninger Principles of Biochemistry:
ISBN-10: 1-4641-2611-9; ISBN-13: 978-1-4641-2611-6; Format: Cloth Text
• Bender, DA: Amino Acid Metabolism, 3rd ed. Wiley, 2012.
• Burton AS, Stern JC, Elsila JE, et al: Understanding prebiotic chemistry
through the analysis of extraterrestrial amino acids and nucleobases in
meteorites. Chem Soc Rev 2012;41:5459.
• Bell EA: Nonprotein amino acids of plants. Significance in medicine, nutrition,
and agriculture. J Agric Food Chem 2003;51:2854.
• Kolodkin-Gal I: d-Amino acids trigger biofilm disassembly. Science
2010;328:627.