- Aromatic amino acids include phenylalanine, tyrosine, and tryptophan. They are classified as nonpolar and play important roles in protein synthesis and as precursors to neurotransmitters, hormones, and pigments. - Phenylalanine and tryptophan are essential amino acids that must be obtained through diet, while tyrosine is non-essential as it can be synthesized from phenylalanine. Dietary sources of these amino acids include meat, eggs, nuts and dairy products. - The metabolism of aromatic amino acids occurs through the shikimate pathway where chorismate is formed and can then be utilized to synthesize tyrosine, phenylalanine, and trypt

1. Basic concepts of Amino acid &
Metabolism of aromatic amino acids
Mrs.R.GLORIA JEMMI CHRISTOBEL
ASSISTANT PROFESSOR
DEPARTMENT OF BIOCHEMISTRY
V.V.Vanniaperumal College For Women,
Virudhunagar, Tamil Nadu.

2. General structure of amino acids
• There are 20 commonly found standard α
aminoacids
• Functional groups of amino acids include
Coo- - carboxyl group,
NH3
+ - amino group,
R- Side chain

3. Classification of aminoacids
• Each AA is represented as 3 letter abbreviation and 1
letter symbol.

4. Classification of Amino Acids Based on
polarity
•Nonpolar, aliphatic amino acids- Gly, Ala,
Pro, Val, Leu, and Ile
•Polar, uncharged amino acids- Ser, Thr,
Cys, Asn, Gln and Met
•Aromatic amino acids-Phe, Tyr and Trp.
Phe and Tyr: benzene rings.Tryptophan:
indole ring.
•Acidic amino acids- Asp and Glu
•Basic amino acids- Lys, Arg, and His.

5. Non standard aminoacids
• 4-Hydroxyproline and 5-hydroxylysine in
collagen.
• 6-N-Methyllysine in myosin
• Ornithine and citrulline

6. Essential and non-essential amino
acids
• Nonessential amino acids can be made by the body,
while essential amino acids cannot be made by the body
so obtained from diet.

7. Aromatic amino acids
Phenylalanine
• An essential α-amino acid with the formula
C6H5CH2CH(NH2)COOH.
• Classified as neutral and nonpolar because of the inert
and hydrophobic nature of the benzyl side chain.
• The codons for L-phe are UUU and UUC.
Dietary Sources:
• Naturally found in - breast milk of mammals. Good
sources - are eggs, chicken, liver, beef, milk, and
• soybeans. Other sources - spinach and leafy greens, tofu,
amaranth leaves, and lupin seeds.

8. Roles & Uses:
• Used in the manufacture of food and drink products.
• Sold as a nutritional supplement for its reputed
analgesic and antidepressanteffects.
• The L-isomer is used to biochemically form proteins,
coded for by DNA. The codons for L-phenylalanine
are UUU and UUC.
• Is a precursor for tyrosine, dopamine, norepinephrine
(noradrenaline), and epinephrine (adrenaline), and the
skin pigment melanin.
• Starting compound used in the flavonoid biosynthesis
in plants.
• The genetic disorder phenylketonuria (PKU) is the
inability to metabolize phenylalanine

9. • TRYPTOPHAN (TRP)
• One of the 23 standard amino acids and an essential amino acid in
the human diet.
• Encoded in the standard genetic code as the codon UGG & Contains
an indole functional group.
• Only L-stereoisomer of trp is used in structural or enzyme proteins.
• The D-stereoisomer is occasionally found in naturally produced
peptides (e.g.-the marine venom peptide contryphan).
Dietary sources:
• A routine constituent of most protein-based foods or dietary proteins.
• Particularly plentiful in chocolate, oats, dried dates, milk, yogurt,
cottage cheese, red meat, eggs, fish, poultry, sesame, chickpeas,
almonds, sunflower seeds, pumpkin seeds, spirulina, bananas, and
peanuts.
• Found at a high level in turkey meat.

10. • Roles & uses:
• An essential amino acid & act as building blocks in protein
biosynthesis
• Functions as a biochemical precursor for the compounds - Serotonin
(a neurotransmitter), Niacin (a vitamin), Auxin (a phytohormone).
• Sold over the counter in the US, Canada, and the UK as a dietary
supplement for use as an antidepressant, anxiolytic, and sleep aid.
• Also marketed for the indication of major depression under various
trade names.
• Available in health food stores as a dietary supplement.
• Potential side effects of trp include nausea, diarrhea,
drowsiness,headache, dry mouth, blurred vision, euphoria, and
nystagmus (involuntary eye movements) etc.

11. TYROSINE (TYR)
• Tyr or 4-hydroxyphenylalanine (from Greek
tyros,meaning cheese), is one of the 23 amino acids
that are used by cells to synthesize proteins.
• A non-essential amino acid with a polar side group.
• Its codons are UAC and UAU.
Dietary sources:
• Found in many high-protein food products such as
chicken, turkey, fish, milk, yogurt, cottage
cheese,cheese, peanuts, almonds, pumpkin seeds,
sesame seeds, soy products, lima beans, avocados, and
bananas.
• Can also be synthesized in the body from
phenylalanine by the enzyme phenylalanine
hydroxylase.

12. Roles & Uses:
• Precursor to neurotransmitters and hormones,
alkaloids, natural phenols, pigments (melanin).
• Tyrosine (or its precursor phenylalanine) is needed
to synthesize the benzoquinone structure which
forms part of coenzyme Q10.
• Useful during conditions of stress, cold, fatigue,
prolonged work and sleep deprivation.
• Reductions in stress hormone levels & stress-
induced weight loss seen in animal trials.
• Increases plasma neurotransmitter levels
(particularly dopamine and norepinephrine).

13. Metabolism of Aromatic amino
acids
• Synthesis of aromatic amino acids follows
Shikimate pathway which leads to the
formation of chorismate.

14. • Prephenic acid is then synthesized by a Claisen
rearrangement of chorismate by Chorismate
mutase. Which can then be utilized for:
• Tyrosine biosynthesis:
Prephenate is oxidatively decarboxylated with
retention of the hydroxyl group to give
phydroxyphenylpyruvate, which is
transaminated using glutamate as the nitrogen
source to give tyrosine and α-ketoglutarate.
• Phenylalanine biosynthesis:
Prephenate is converted to phenylpyruvate by
prephenate dehydratase.Then phenylpyruvate
is transaminated to give phenylalanine by
phenylalanine aminotransferase.

16. • Tryptophan biosynthesis:
Chorismate produces anthranilate which condenses
with phosphoribosylpyrophosphate (PRPP) to
make N-5-Phosphoribosyl anthranilate.After ring
opening of the ribose moiety and following
reductive decarboxylation, indole-3-
glycerolphosphate is produced, which in turn is
transformed into indole.In the last step,
tryptophan synthase catalyzes the formation of
tryptophan from indole and the amino acid
serine.

18. THANK YOU