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

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

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

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

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

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

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

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

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

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

Tertiary Structure -non-repeating folding

Quaternary structure- multimeric proteins

Review: the four levels of protein structure

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

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

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