Lecture 5.docx

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Biology - Biological Sciences
BSC 2010

Lecture 5 Concept 3.2 Proteins are Polymers with Important Structural and Metabolic Roles  Oligopeptides or peptides—short polymers of 20 or fewer amino acids (some hormones and signaling molecules)  Polypeptides or proteins range in size from insulin, which has 51 amino acids, to huge molecules such as the muscle protein titin, with 34,350 amino acids.  Amino acids are linked in condensation reactions to form peptide linkages or bonds.  Polymerization takes place in the amino to carboxyl direction.  There are four levels of protein structure: o 1. Primary- held together by peptide bonds/ covalent bonds o 2. Secondary- held by hydrogen bonds o 3. tertiary o 4. Quaternary  Secondary structure: regular, repeated spatial patterns in different regions, resulting from hydrogen bonding  There are 2 major types of secondary structure: o 1. α (alpha) helix—right-handed coil o 2. β (beta) pleated sheet—two or more polypeptide chains are extended and aligned  Tertiary structure is the final, folded, 3-D shape of a polypeptide.  Tertiary structure is determined by interactions between R groups, rather than interactions between backbone constituents  Interactions between R groups determine tertiary structure. o Disulfide bridges (covalent bond) hold a folded polypeptide together o Hydrogen bonds stabilize folds o Hydrophobic interactions side chains can aggregate o van der Waals interactions between hydrophobic side chains o Ionic interactions form salt bridges  Quaternary structure o Two or more polypeptide chains (subunits) bind together by hydrophobic and ionic interactions, and hydrogen bonds. o These weak interactions allow small changes that aid in the protein’s f
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