Protein Chemistry

1. Protein Chemistry Ass.Prof./Naglaa Fathy Alhusseini Naglaa Alhusseini

2. Proteins chemistry • Definition: Proteins are organic nitrogenous compound of high molecular weight, consisting largely or entirely of α-amino acids united together by peptide linkages. They are composed of carbon, hydrogen, oxygen and nitrogen, many types of proteins may contain sulfur. Nitrogen is a characteristic component of proteins, forming about 16% of their weight. Naglaa Alhusseini

3. Functions of proteins: • Synthesis of tissue proteins e.g., contractile protein of muscles, collagen …etc... • Synthesis of cell organelles as cell membrane ,receptors…….etc • Synthesis of enzymes • Synthesis of milk proteins. • Synthesis of plasma proteins. • Synthesis of protein hormones. • Synthesis of nucleoproteins. Naglaa Alhusseini

4. Biological importance of proteins: • Fibrous or structural protein • Keratin- elastin • Collagen- reticulin • Muscle protein (Myocin and Actin) • Protein of cell membrane • Protein of cytoplasm • Functional protein • Enzyme • Hormones • Receptors • Igs • Plasma protein • Hemoglobin Naglaa Alhusseini

5. Questions • 1- What are the biological importance of proteins? • All the following are functional protein EXCEPT • Igs • enzyme • Collagen • Hemoglobin Naglaa Alhusseini

6. Amino Acids • Amino acid is an organic acid containing one or more amino group and carboxylic group (COOH) • carboxylic group (COOH) and amino group (NH2) are both attached to the α-carbon • They are the building units of protein. Naglaa Alhusseini

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8. Amino acids found in proteins are of L-configuration, this means that the amino group to the left and the hydrogen to the right of the a-carbon • D-amino acid • L-amino acid Isomerism of amino acids Naglaa Alhusseini

9. Functions of amino acids: Question • Synthesis of structural and functional proteins. • L-amino acid and their derivatives play a role in intracellular functions as nerve impulse transmission and regulation of cell growth. • Biosynthesis of purines, pyrimidines, urea and porphyrins. • L-and D-amino acids are present in polypeptide antibiotics secreted by microorganisms. True or false ?? Naglaa Alhusseini

10. Classifications: Amino acids can be classified by different classification: • Chemical classification. • Nutritional classification. • Metabolic classification. • Reaction classification (Charge properties). Naglaa Alhusseini

11. 1. Chemical classification: A) Aliphatic amino acids: have no ring; These amino acids may be subclassified into: • Branched chain amino acids: as valine, leucine, and isoleucine. • Hydroxy amino acids: as serine and threonine. • Sulphur containing amino acids: as cysteine and methionine. • Amino acids with amide group: as asparagine and glutamine. Naglaa Alhusseini

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15. Aromatic amino acids Naglaa Alhusseini

16. Heterocyclic amino acids: They have heterocyclic ring as histidine, tryptophan, proline and hydroxyproline. Naglaa Alhusseini

17. Reaction classification ( charge properties): • Non polar (Neutral): having equal number of amino and carboxyl groups e.g. alanine, serine, valine …etc • Polar Basic AA: having more than one amino group and one carboxyl e.g. arginine, lysine, histidine …etc • Polar (Acidic): having one amino group and two carboxyl e.g. glutamic acid and asparticacid Naglaa Alhusseini

18. Polar Basic AA: having more than one amino group and one carboxyl e.g. arginine, lysine, histidine Naglaa Alhusseini

19. Acidic Amino Acids and their Amides Naglaa Alhusseini

20. B) Aromatic amino acids:They have benzene ring in their side chains like • Phenylalanine • Tyrosine • Tryptophan C) Heterocyclic amino acids:They have heterocyclic ring as • Histidine, • Tryptophan, • Proline and hydroxyproline. Naglaa Alhusseini

21. 2. Nutritional classification: They are classified into three groups: • Essential amino acids: They are amino acids which cannot be synthesized in the body and must be taken in diet; phenylalanine, methionine, isoleucine, leucine, lysine, valine, threonine and tryptophan. • Semi essential amino acids: They are amino acids required in the food of growing children not in the food of adult as histidine and arginine. • Non essential amino acids: can be synthesized inside the body as glycine, alanine, serine, cysteine, cystine, aspartic, tyrosine, glutamic, proline and hydroxyproline Naglaa Alhusseini

22. Memory Aid for Essential Amino Acids Any Help In Learning These Little Molecules Proves Truly Valuable Arginine –Histedine – Isoleosine – Leosine – Threonine- Lysine- Methionine –Phyenylalanine- Tryptophan –Valine Naglaa Alhusseini

23. 3. Metabolic classification: According to their fate in the body they are classified into three groups: • Glucogenic amino acids: give glucose inside the body as glycine, alanine, aspartic and glutamic. • Ketogenic amino acid: gives ketone bodies as leucine. • Glucogenic and ketogenic amino acids: They give both glucose and ketone bodies as lysine, tryptophan, tyrosine, phenylalanineand isoleucine. Naglaa Alhusseini

24. Clinical importance of amino acids and their derivatives • L-tyrosine is sometimes recommended by practitioners as helpful for weight loss, clinical depression. • Dopamine derived from tyrosine is a neurotransmitter. • Thyroxine is an important thyroid hormone from tyrosine. • Gamma aminobutyric acid (GABA) derived from glutamic acid; which is a neurotransmitter. • Cycloserine derived from serine is an anti-tuberculous drug. • Arginine stimulates the healing of burning wound and other wounds. • Arginine together with lysine can limit herpes attacks (bladders in the mouth) for people that carry this virus. • Cysteine can help to recover the damage by smoking and alcohol. • Glutamine can give the mind new energy and can help to prevent and treat inflammations of the large intestine. Naglaa Alhusseini

25. Which of the following amino acid is an acidic amino acid. • Arginine • Aspartic acid • Lysine • Leucine Naglaa Alhusseini

26. Which of the following amino acid is both neutral and aromatic in nature? • Alanine • Histidine • Plyenylalanine • Proline Naglaa Alhusseini

27. All amino acids which both glucogenic and ketogenic are essential amino acids EXCEPT • Phenylalanine • Tyrosine • Glycine • Alanine Naglaa Alhusseini

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37. Amino acid not found in proteins: Few amino acids are not found in proteins (non-protein amino acids) • L-Ornithine is an intermediate of urea cycle . It is formed from arginine • L- citrulline is intermediate of urea cycle . It is formed from ornithine • Homoserine is an intermediate in methionine metabolism. It is formed from serine. • GABA: γ amino butyric acid :is an inhibitor neurotransmitter • DOPA: Dihydroxyphenylalanine : Is formed from tyrosine and precursor for biosynthesis of epinephrine and norepinephrine • β alanine : occurs in coenzyme A , Pantothenic acid and it is also formed during degeneration pyrimidine nucleotides Selenocysteine is an amino acid containing selenium ( trace element). It is considered as the 21st amino acid since it is coded by the stop codon UGA. Examples of proteins containing selenocysteine are glutathione peroxidase enzyme and 5'deiodinase . Naglaa Alhusseini

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