Amino Acids (1) IUA, 2012
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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.
Atif Hassan Khirelsied

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.
Atif Hassan Khirelsied

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.
Atif Hassan Khirelsied

The Functions of Amino Acids
• Precursor for various biologic substances• Precursor for various biologic substances.
– Glucose.
– Heme.
– Purines and pyrimidines.
– Neurotransmitters.
– Hormones– Hormones
Atif Hassan Khirelsied

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.
Atif Hassan Khirelsied

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
Atif Hassan Khirelsied

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
Atif Hassan Khirelsied

The aliphatic non‐polar amino acids
This class include:
1 Glycine1. Glycine
2. Alanine
3. Valine
4. Leucine 4. Leucine
5. Isoleucine
Atif Hassan Khirelsied

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
Atif Hassan Khirelsied

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.
Atif Hassan Khirelsied

The aliphatic non‐polar amino acids
3. Valine, Val , (V).
4 Leucine 4. Leucine, Leu, (L).
5. Isoleucine, Ile, (I).
Atif Hassan Khirelsied

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.
Atif Hassan Khirelsied

The sulphur containing amino acids
7. CysteineCys, (C).
MethionineMet (M)Met (M)
Note Met is also an aliphatic non-polar amino acid
Atif Hassan Khirelsied

The hydroxyl containing amino acids
8. SerineSer, (S).
9. ThreonineThr, (T).
T iTyrosineTyr, (Y).
Atif Hassan Khirelsied

The acidic amino acids and their amides
10. Aspartic acidAsp,(D)
11. AsparagineAsn, (N).
Atif Hassan Khirelsied

The acidic amino acids and their amides
12.Glutamic acidGlu, (E).Glu, (E).
13 Gl t i13. GlutamineGln, (Q).
Atif Hassan Khirelsied

The basic amino acids
14 Araginine14. AraginineArg, (R).
15. LysineLys, (K).Lys, (K).
16.HistidineHis (H)
Atif Hassan Khirelsied
His, (H).

The aromatic amino acids
17. PhenylalaninePhe, (F).
18 Tyrosine18. TyrosineTyr, (Y).
19 Tryptophan19. TryptophanTrp, (W).
Atif Hassan Khirelsied

The imino acid
20. ProlinePro, (P).
The nitrogen atom is secondarily attached to the side‐
chainschains.
Atif Hassan Khirelsied

The cystine
Atif Hassan Khirelsied

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.
Atif Hassan Khirelsied

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).
Atif Hassan Khirelsied

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.
Atif Hassan Khirelsied