2. Metabolic fuels and Dietary components Lecture - 3 By Dr. Abdulrahman Al-Ajlan

3. Peptide Bond Formation  The covalent binding of a α- amino group of one amino acid with the carboxyl group of a second amino acid with the elimination of water, results in the formation of a peptide bond.

4. Continue Amino acids in proteins (or polypeptides) are joined together by peptide bonds.

5.  Polymers of amino acids formed in this way are known as peptides.

6. A dipeptide contains two amino acid residues; a tripeptide contains three. An amino acid chain with less than 25 amino acid residues is called an oligopeptide while a poly peptide has more than 25 amino acids. A protein may consist of a long polypeptide or several polypeptide subunits. Normally, the amino acid residues found in peptides are named in the order starting from the N-terminal end.

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8. Physiologically important oligopeptides and peptides 1.Glutathione  Glutathione is an important tripeptide present in all tissues. It contains glutamic acid, cysteine, and glycine

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11. Continue… Is a tripeptide (γ-glutamyl cysteinyl glycine), the functions of GSH include the following A.Preventing peroxide and free radical mediated cell injury. B.Transporting amino acids across membranes in kidney.

12. Continue C.Functioning as an intracellular reducing agent, glutathione helps to maintain the –SH groups of amino acids in various proteins in a reduced, active state D.Detoxification of foreign compound (e.g. drugs), by forming water-soluble glutathione conjugates.

13. Continue 2.Oxytocin and Vasopressin (antidiuretic hormone, ADH)  These are hormone secreted by the posterior lobe of the pituitary gland.  Oxytocin stimulates the contraction of the uterus during labor and facilitates ejection of milk from the breast during nursing.

14. Continue Oxytocin consist of a nine amino acid, oxytocin differs from antidiuretic hormone in two of the nine amino acids

15.  Both hormones are packaged into granules and secreted along with carrier proteins called neurophysins. And transported down axons of the posterior pituitary for secretion into blood  Peptide that is synthesized in hypothalamic neurons

16. Vasopressin decreases water excretion by the kidney.

17. 3- Angiotensin Its function regulation of arterial blood pressure.

18. Peptides Many hormones in the body (e.g. insulin, growth hormone) are polypeptides. These hormones are frequency given to patients to correct deficiency states. In general, proteins may have either of two tertiary forms- globular or fibrous. Bonds that help to maintain the stability of the tertiary structure include:

19. Continue.. 1.Hydrophobic bonds formed between amino acids with hydrophobic R- groups (e.g. ala, leu, Ilo, phe, trp) 2.Hydrogen bonding between amino acid side chains. 3.Ionic or electrostatic bonds between Amino acids containing oppositely charged side chains. 4.Covalent bonds; the most common type is the disulphide bond of cys between cys residues.

20. Hydrogen bonds

21. In general, fibrous proteins (e.g. collagen, α-keratin) are elongated and water insoluble, while globular proteins are spherical and water soluble