etee

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.