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Bio-Molecules: Proteins

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Northeastern University
BIOL 1117
Christopher Richardson

Bio-Molecules: Proteins 9/18/13 • protein: a polymer of amino acids • amino acid is central carbon with 3 attachments o amino group (NH2), carboxyl group (COOH) and radical group (R group) o R group attached to central carbon o This R group may be a single H or a complex ring of C • 20 amino acids used to make the proteins are identical except for the R group • properties of amino acid determined by the R group • Naming of Peptides o peptide: any molecule composed of two or more amino acids joined by peptide bonds o peptide bond joins the amino group of one amino acid to the carboxyl group of the next • Protein Structure and Shape o Primary structure  Sequence of amino acid which is encoded in the genes o Secondary structure  Coiled or folded shape held together by hydrogen bonds: alpha helix or beta sheets o Tertiary structure  Further bending and folding of proteins • globular proteins –compact tertiary structure well suited for proteins embedded in cell membrane and proteins that must move about freely in body fluid • fibrous proteins – slender filaments better suited for roles as in muscle contraction and strengthening the skin  Due to hydrophobic R groups which avoid water and hydrophilic R groups which contact water; Van der Waals forces are also involved o Quaternary structure  Associations of two or more separate polypeptide chains  Using noncovalent bonds such as ionic bonds and hydrophilic- hydrophobic interactions • Protein Conformation and Denaturation o Proteins have complex structure with coils and folds; even slight changes to conformation can disrupt or interfere with protein function o Conformation: unique three dimensional shape of protein crucial to function  Ability to reversibly change their conformation • enzyme function • muscle contraction • opening and closing of cell membrane pores o Denaturation  Extreme conformational change that disrupts physiological function • usually irreversible change, in terms of function • extreme heat or pH • only when the peptide bond breaks or destroys the protein at the primary level is the protein permanently destroyed o Conjugated Proteins  Proteins that contain a non-amino acid moiety  Hemoglobin contains four complex iron containing rings called a heme moieties o Protein Functions  Structure  Communication • Receptors to which signal molecules bind  Membrane Transport • Channels and carrier proteins in cell membranes  Catalysis • Enzymes are protein catalysts  Recognition and Protection • Antibodies and clotting proteins • Some proteins serve to recognize and fight invading organisms  Movement • For example, motor proteins cause intracellular transport and muscle contraction  CellAdhesion o Enzymes  Enzymes: proteins that function as biological catalysts • Permit reactions to occur rapidly at normal body temperature • Lower temperatu
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