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Diverse Macromolecules

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V. proteins are macromolecules that are polymers formed from amino acids monomers A. proteins have great structural diversity and perform many roles B. roles include enzyme catalysis, defense, transport, structure/support, motion, regulation; protein structure determines protein function

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C. proteins are polymers made of amino acid monomers linked together by peptide bonds 1.amino acids consist of a central or alpha carbon; bound to that carbon is a hydrogen atom, an amino group (-NH 2 ), a carboxyl group (-COOH), and a variable side group (R group) the R group determines the identity and much of the chemical properties of the amino acid

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there are 20 amino acids that commonly occur in proteins; pay attention to what makes an R group polar, nonpolar, or ionic (charged) and thus their hydrophobic or hydrophilic nature

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plants and bacteria can usually make their own amino acids; many animals must obtain some amino acids from their diet (essential amino acids )

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2.the peptide bond joins the carboxyl group of one amino acid to the amino group of another; is formed by a condensation reaction 2.two amino acids fastened together by a peptide bond is called a dipeptide, several amino acids fastened together by peptide bonds are called a polypeptide

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D. the sequence of amino acids determine the structure (and thus the properties) of a protein E. proteins have 4 levels of organization or structure 1.primary structure (1 ) of a protein is the sequence of amino acids in the peptide chain

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2.secondary structure (2 ) of a protein results from hydrogen bonds involving the backbone, where the peptide chain is held in structures, either a coiled -helix or folded -pleated sheet; proteins often have both types of secondary structure in different regions of the chain

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3. tertiary structure (3 ) of a protein is the overall folded shape of a single polypeptide chain, determined by secondary structure combined with interactions between

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4.quaternary structure (4 ) of a protein results from interactions between two or more separate polypeptide chains the interactions are of the same type that produce 2 and 3 structure in a single polypeptide chain when present, 4 structure is the final three- dimensional structure of the protein (the protein conformation) example: hemoglobin has 4 polypeptide chains not all proteins have 4 structure

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Tertiary Structure of Hemoglobin

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5.ultimately the secondary, tertiary, and quaternary structures of a protein derive from its primary structure, but molecular chaperones may aid the folding process 6.protein conformation determines function

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7.denaturation is unfolding of a protein, disrupting 2 , 3 , and 4 structure changes in temperature, pH, or exposure to various chemicals can cause denaturation denatured proteins typically cannot perform their normal biological function denaturation is generally irreversible

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F. enzymes are biological substances that regulate the rates of the chemical reactions in living organisms; most enzymes are proteins (covered in some detail later in this course) G. related compounds amino acids; modified amino acids; polypeptides too short to be considered true proteins; and modified short polypeptides