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PROTEINS The most complex and multifunctional class of organic molecules Most genes are instructions for making protein molecules Large molecules with complex 3-dimensional shapes Polymers of amino acids

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Protein functions Catalytic enzymes control reactions Structural e.g. collagen, keratin, silk Storage of amino acids for growth Transport e.g. O 2 and hemoglobin Hormones communication among cells Receptors receiving chemical signals Contractile e.g. actin and myosin Defensive e.g. antibodies

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CC O O-H H2N H2N R Amino Carboxyl Functional group varies- >20 kinds Ionized form Amino acid structure O-O- CC O +H3N +H3N R H H

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O-O- CC O +H3N +H3N H asymmetric -carbon enantiomers Only L-forms are made and used by organisms

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The 20 amino acids of proteins: nonpolar, hydrophobic side chains

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The 20 amino acids of proteins: polar and electrically charged side chains

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Proteins have complex, 3-D shapes Alternative diagrams of the protein lysozyme

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the amino acid sequence of a protein Determined by the genetic information that directs protein synthesis Primary structure

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A single amino acid substitution in a protein causes sickle- cell disease

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Secondary structure repetitive folding due to H-bonds between amino and carbonyl -helix and -sheet

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Tertiary Structure -non-repeating folding

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Quaternary structure- multimeric proteins

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Review: the four levels of protein structure

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Disruption of 2, 3, or 4 structure by heat, pH, or ions = cooking Denaturation

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NUCLEIC ACIDS (DNA, RNA) =polynucleotides polymers of nucleotides Nucleotide structure: phosphate Nitrogenous base pentose N N

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Nucleotide function nucleoside triphosphates- (ATP, GTP) are energy carriers Monomers for building polynucleotides Polynucleotide function DNA, RNA are information carriers Some RNAs are catalysts More about nucleic acids later, when we consider molecular genetics