Understanding Peptide Bonds and Peptides: Structure, Formation, and Functions, Thesis of Law

Download Understanding Peptide Bonds and Peptides: Structure, Formation, and Functions and more Thesis Law in PDF only on Docsity! PEPTIDE Mr. Basanta Gelal Assistant Professor Department of Biochemistry BPKIHS, Dharan OBJECTIVES Introduction Characteristics of Peptide bond Peptides Ramachandran plot PEPTIDE BONDS  Covalent bond joining alpha carboxyl group of one amino acid to amine of another amino acid  Formation of CO-NH bond/amide bond.  The equilibrium of this reaction lies on the side of hydrolysis rather than synthesis under most conditions  The biosynthesis of peptide bonds requires an input of free energy.  Hydrolysis of a peptide bond is an exergonic reaction, it occurs slowly because of its high activation energy. PEPTIDE BOND FORMATION , im H;N—CH—C—OH + H—N—CH—COoO-  Repeating part called the main chain or backbone  Variable part : side chains  In late 1950s and early 1960s revealed that the amino acid sequences of proteins are genetically determined. Protein: Unique, precisely defined amino acid sequence  Amino acid sequence is called primary structure. STRUCTURE OF PEPTIDES PEPTIDE BOND 1. Partial double bond  CN distance in a peptide bond is typically 1.33 Å, C-N single bond (1.49 Å) C=N double bond (1.27 Å) C-N in peptide single bond (1.33) 2. Rigid and Planer resisting free rotation and hence stabilize protein.  6 atoms lie on same plane  O of C=O is trans to H of amide PEPTIDE BOND C-N double bond character in amide (peptide) bonds @ PEPTIDE BOND 3. Peptide bonds are uncharged but polar. 4. >99.95%, peptide bonds between amino acid residues (except Proline), are in the trans configuration. Glutathione (γ-L-Glutamyl- L-cysteinylglycine) is an important antioxidant in animal cells Melanostatin (prolyl-leucyl- glycinamide) is a peptide hormone produced in the hypothalamus that inhibits the release of melanocyte-stimulating hormone (MSH) Thyrotropin-releasing hormone TRIPEPTIDE Nona peptide  Oxytocin  Vasopressin (antidiuretic hormone) Polypeptide: Prolactin is composed of 199 amino acids PEPTIDES: A VARIETY OF FUNCTIONS • Hormones and pheromones • insulin (think sugar) • oxytocin (think childbirth) • sex-peptide (think fruit fly mating) • Neuropeptides • substance P (pain mediator) • Antibiotics • polymyxin B (for Gram – bacteria) • bacitracin (for Gram + bacteria) • Protection, e.g., toxins • amanitin (mushrooms) • conotoxin (cone snails) • chlorotoxin (scorpions) Pauling and Corey found peptide bond cannot rotate freely. Rotation occurs at N-Cα and Cα-C, φ & ψ angles respectively. In a pair of linked amino acids, six atoms (Cα, C, O, N, H, and Cα) lie in a plane. N C O Cα N C Cα N C Cα RAMACHANDRAN PLOT  Given By G.N. Ramachandran.  Plot gives the possible values of ɸand ψ angles in peptide bonds.  Dark shaded area- conformation that involve no steric overlap.  Medium blue- conformation allowed at extreme limits for unfavourable atomic contacts.  Light blue-conformation that are permissible if a little flexibility is allowed in the bond angle. y (degrees) Antiparallel Collagen triple B sheets Parallel 6B sheets /Right-twisted 8 sheets +180 120 60 -60 -120 -180 -180 0 o (degrees) Left-handed a helix Right-handed a helix +180