بسم الله الرحمن الرحيم

1. بسم الله الرحمن الرحيم

2. Amino Acids

3. Amino Acids • By the end of this lecture the student will understand: • Amino acids, structure and classification • Amphipathic character, pK, pI • Peptides and Peptide bond • Examples of related compounds

4. Proteinsare the most • Abundant وفرة& • functionally diverse • molecules in living systems. • = Abundant & Variable متغيرة او مختلفة

5. Enzymes and Hormones (polypeptide) • control metabolism الأيضin the body, • contractile proteins in muscle • Control movement.

6. In bone,  the protein collagen • forms a framework for the deposition of calcium phosphate crystals

7. In the bloodstream مجرى الدم , proteins, such as • hemoglobin and plasma albumin زلال, transport molecules essential to life, • immunoglobulinsالمناعي fight infectious bacteria and viruses.

8. Despite of the incredible diverse (Variable) functions of proteins , They all share the commonstructural feature of being linearpolymers of amino acids. على الرغم من وظائف (متغير) لا يصدق متنوعة من البروتينات،انهم جميعا تشترك في سمة مشتركة الهيكلية لكونها البوليمرات الخطية من الأحماض الأمينية.

9. In nature  >300 different amino acids (a.a.) only20are commonly found as constituents of mammalianproteins. These are the only amino acids that are coded for by DNA, the genetic material in the cell

10. Each amino acid (except for proline, which has a secondary amino group) has a carboxylgroup (COOH), a primaryaminogroup, and a distinctive side chain (“R-group”) bonded to the α-carbon atom

11. The α-carbon of each amino acid (except glycine) is attached to four different chemical groups and is, therefore, a chiral or optically active carbon atom. • Only the L-form of amino acids is found in proteins synthesized by the human body.

12. At physiologic pH (approximately pH 7.4), the carboxyl group is dissociated, forming the negatively charged carboxylate ion (–COO-), and the amino group is protonated (–NH3+). In proteins, almost all of these carboxyl and amino groups are combined in peptide linkage and, in general,  are not available for chemical reaction except for hydrogen bond formation

13. The nature of the side chains Will determines the role an amino acid plays in a protein. So, weclassify the amino acids according to properties of their side chains polar (that is, have an unevendistribution of electrons, such as acids and bases; nonpolar (that is, have an evendistribution of electrons)

14. Classification of amino acids according to properties of their side chains A. Amino acids with nonpolarside chains B. Amino acids with unchargedpolarside chains C. Amino acids with acidic (polar ) side chains D. Amino acids with basic(polar ) side chains

15. nonpolar (hydrophobic ) R groups: They have no reacting group. • a nonpolar side chain does not : • does not bind or give off protons • does not participate in hydrogen or ionic bonds These side chains can be thought of as “oily” or lipid-like,   a property that promotes hydrophobicinteractions

17. Location of nonpolar amino acids in proteins: • In proteins found in aqueous solutions—= a polar environment—the side chains of the nonpolar amino acids tend to cluster together in the interior of the protein. fill up the interior of the folded protein and help give it its three-dimensional shape. 3D

18. Location of nonpolar amino acids in proteins: • This phenomenon is the result of the hydrophobicityof the nonpolar R-groups, (like droplets of oil in water).

19. Location of nonpolar amino acids in proteins: For proteins that are located in a hydrophobic environment, such as a membrane, the nonpolar R-groups are found on the outside surface of the protein, interacting with the lipid environment

20. Sickle cell disease is a pathology that results from the substitution of polar glutamate by nonpolar valinein the β subunit of hemoglobin مرض فقر الدم المنجلي يحصل نتيجة استبدال حمض أميني أساسي وهو الجلوتامين القطبي بواسطة الفالين الغير قطبي في وحدة البيتا من الهيموجلوبين

21. Polar ( hydrophilic) uncharged or charged R groups : contain an active reactive group R groups • Amino acids with unchargedpolarside chains • Amino acids with acidic (polar ) side chains • Amino acids with basic (polar ) side chains

22. A. A. with polar uncharged side chains Serine, threonine, and tyrosine each contain a polar hydroxyl group that can participate in hydrogen bond formation تشارك في تكوين روابط هيدروجينية

23. A. A. with polar uncharged side chains The side chains of asparagine and glutamine each contain a carbonyl group and an amide group, both of which can also participate in hydrogen bonds.

24. Amino acids with acidic side chains The amino acids aspartic and glutamic acid are proton donors. At physiologic pH, the side chains of these amino acids are fully ionized, containing a negatively charged carboxylate group (–COO-)  called aspartate or glutamate to (negatively charged at physiologic pH

25. Amino acids with Basic side chains The side chains of the basic amino acids accept protons.At physiologic pH the side chains of lysine and arginine are fully ionized and positively charged.

26. Amino Acids classification According to the nutritional value ( biological value ) : • A. Essential amino acids : • They can not be synthesized by human body. • It must be taken in the diet. • They are 10: • valine, leucine, isoleucine, • phenylalanine, tryptophan, • lysine, arginine,histidine • methionine, and threonine.

27. B. Non essential amino acids: • can be synthesized in the body, • they include: glycine, alanine, serine, cysteine, aspartic, aspargine, glutamic, glutamine, tyrosine and proline.

28. Each amino acid name has an associated • three-letter abbreviation and • a one-letter symbol

29. Isoelectric point (IEP) or pI It is the pH at which an amino acid carries equal positive and negative charge (i.e. electrically neutral).

30. Amphoteric properties In solution, amino acids behave as acids and alkalis due to the presence of acidic group (-COOH) and basic group (-NH2). On complete ionization of neutral amino acids as dipolar ions (Zwitterions) , they carry equalboth negative and positive charges

31. Zwitterions

32. Peptides & Bonds between A. A.

33. A. Covalent bonds 1. Peptidebonds 2. Disulfide bonds

34. B– Non Covalent Bonds weak bonds, can be separated easily 1. Hydrogen bonds 2.Hydrophobicinteractions 3.Electrostatic bonds ( -,- / +,+ & -,+)

35. Peptide bond is a dehydration reaction. • It a rigid & strong • Broken by enzymatic action or by strong acid or base

36. 2. Disulfide bonds They occur between 2 cysteine residues inthe same polypeptide chain or in different polypeptide chains

37. Peptides: A peptide consists of two or more amino acid residues linked by peptide bonds. 2 A.A. = Dipeptide 3 A.A. = Tripeptide 10 -100 A.A = Polypeptide peptides containing > 100 A.A.  = Protein insulin (51) Glucagon (29)

38. Glutamate Cysteine Glycine • Glutathione: • It is a tripeptide. • It is an important reducing agent, since it is present in reduced (G-SH) and oxidized forms (G-S-S-G). Many hormones are polypeptides e.g. insulin (51) , glucagons (29),

39. thank you

40. All free amino acids, plus charged amino acids in peptide chains, can serve as buffers.

41. Side chains as sites of attachment for other compounds: The polar hydroxyl group of serine, threonine, and, rarely, tyrosine, can serve as a site of attachment for structures such as a phosphate group. In addition, the amide group of asparagine, as well as the hydroxyl group of serine or threonine, can serve as a site of attachment for oligosaccharide chains in glycoproteins