Amino Acids (1)

Atif H. Khirelsied, Ph.D.Atif H. Khirelsied, Ph.D.  

Department of BiochemistryFaculty of Medicine

International University of Africa, Khartoum, Sudan

Amino Acids

1. Amino acids (aa) are organic acids with an amine1. Amino acids (aa) are organic acids with an aminegroup. 

2. They are the "building blocks" of proteins.

3. Have a wide range of diverse biological functions.

4 There are more than 300 aa in nature4. There are more than 300 aa in nature.

5. Only 20 L‐α‐amino acids are found in proteins.Atif Hassan Khirelsied

Amino Acids

5. D‐Amino acids occur in bacteria and peptide ibi iantibiotics.

6 S l h i id f d i i6. Several other amino acids are found in non‐protein substances. 

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Amino Acids Structure

A typical amino acid has a primary amino group, a carboxyl group, a hydrogen atom and a side‐chain (R group) attached to a chiral α carbon atomchiral α carbon atom.

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Amino Acids Structure

The Functions of Amino Acids

• They are the "building blocks" of proteins.y g p

• Are important (essential) nutrients• Are important (essential) nutrients.

• Components of various biomolecules e.g., serine in phospholipids.

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The Functions of Amino Acids

• Precursor for various biologic substances• Precursor for various biologic substances.

– Glucose.

– Heme.

– Purines and pyrimidines.

– Neurotransmitters.

– Hormones– Hormones

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Amino acids, isomerism & optical activity

Enantiomers

All standard α‐amino acids except glycine and proline have chiral

carbons (the αC), thus exist in pairs of (D) and (L) enantiomers.

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Amino acids classifications

• Amino acids can be classified according to:

1 Chemical nature of R groups1. Chemical nature of R‐groups

2. Solubility

3.  Dietary importance

4. Metabolic fate

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Amino acids; classification by R-group

• According to the chemical nature of the side chain,According to the chemical nature of the side chain, amino acids can be classified into:1 Aliphatic non‐polar amino acids1. Aliphatic non‐polar amino acids.

2. Sulfur containing amino acids.

3 H d l t i i i id3. Hydroxyl containing amino acids.

4. Aromatic amino acids.

5. Acidic amino acids and their amides.

6. Basic amino acids.

7. Imino acid

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The aliphatic non‐polar amino acids

This class include:

1 Glycine1. Glycine

2. Alanine

3. Valine

4. Leucine 4. Leucine

5. Isoleucine

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The aliphatic non‐polar amino acids

1 Glycine 1. Glycine

(Gly or G).

Glycine

•Is the smallest amino acid.

•Has the simplest structure.p

•Does not exist as a pair of stereoisomers

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The aliphatic non‐polar amino acids

2 Alanine2. Alanine

(Ala or A)( )

Alanine

•Is aliphatic amino acid.

•Has a methyl group in the side-chain position.

•Hydrophobic.

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The aliphatic non‐polar amino acids

3. Valine, Val , (V).

4 Leucine 4. Leucine, Leu, (L).

5. Isoleucine, Ile, (I).

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The aliphatic non‐polar amino acids

6.Methionine, Met, (M).

NOTE

The aliphatic side‐chains of Ala, Val, Leu, Ile  & Met are 

non‐reactive, hydrophobic.

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The sulphur containing amino acids

7. CysteineCys, (C).

MethionineMet (M)Met (M)

Note Met is also an aliphatic non-polar amino acid

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The hydroxyl containing amino acids

8. SerineSer, (S).

9. ThreonineThr, (T).

T iTyrosineTyr, (Y).

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The acidic amino acids and their amides

10. Aspartic acidAsp,(D)

11. AsparagineAsn, (N).

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The acidic amino acids and their amides

12.Glutamic acidGlu, (E).Glu, (E).

13 Gl t i13. GlutamineGln, (Q).

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The basic amino acids

14 Araginine14. AraginineArg, (R).

15. LysineLys, (K).Lys, (K).

16.HistidineHis (H)

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His, (H).

The aromatic amino acids

17. PhenylalaninePhe, (F).

18 Tyrosine18. TyrosineTyr, (Y).

19 Tryptophan19. TryptophanTrp, (W).

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The imino acid

20. ProlinePro, (P).

The nitrogen atom is secondarily attached to the side‐

chainschains.

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The cystine

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Amino acids classification by solubility

• Two classes of amino acids based upon whether the R‐group is;R group is;

•1 H d h bi1. Hydrophobic 

2. Hydrophilic. 

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Amino acid classification by dietary importance.

Some amino acids can be formed from metabolic 

intermediates in the mammalian cells thus are notintermediates in the mammalian cells, thus are not 

necessary taken in food (Dietary non‐essential) .

Other amino acids must be obtained from diet, thus 

they are termed (Dietary essential).

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Amino acids classification by metabolic fate

Amino acids can also be classified according to the end product of their carbon skeleton catabolism into: p

1 Gluogenic glucose producing1. Gluogenic – glucose producing

2. Ketogenic – ketones producing

3. Keto and glycogenic.

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