Proteins Macromolecules slides 31 33 of part 1 2 19 part 2 General amino acid structure polypeptide synthesis pg 48 3 11 Proteins are composed of one or more polypeptides Polypeptide single chain polymer of amino acid The monomer building blocks subunits of polypeptides are amino acids Side chain R group H2N R central carbon C COOH H Dipeptide Peptide bond Polypeptide synthesis Amino terminus N terminus Amino terminus Dipeptide 3 11 Carboxyl terminus C terminus Carboxyl terminus Side chains R groups Backbone Indicate everything you can about this polypeptide Why N and C termini are charged Functional groups and properties of side chains Positions of peptide bonds Recognize each amino acid subunit The 20 amino acids Nonpolar amino acids hydrophobic side chains 3 12 The 20 amino acids Polar amino acids hydrophilic side chains 3 12 The 20 amino acids 3 12 Electrically charged amino acids side chains with acidic or basic functional groups Acidic negatively charged Basic positively charged Polypeptide chains can be short or long Short chains 10 50 amino acids often called peptides Example insulin a peptide hormone 51 amino acids Polypeptides generally 100 1000 amino acids Largest titin a muscle protein 26 000 amino acids Proteins consist of one or more polypeptides twisted folded and coiled into a unique shape that determines its function The four levels of protein structure primary secondary 3 13 tertiary Animations quaternary Primary structure 3 13 Primary 1 structure unique sequence of amino acids in a polypeptide order and length specified directly by the nucleotide sequence of the gene encoding the polypeptide Amino terminus Amino acid subunits 1 structure determines other levels of structure Carboxy terminus Secondary structure 3 13 Secondary 2 structure regular repeated pattern of coils or folds created by predictable patterns of hydrogen bonding between atoms along the polypeptide backbone not between R groups helix pleated sheet Tertiary structure Tertiary 3 structure the overall three dimensional shape of a polypeptide Results from interactions between side chains R groups 3 13 Tertiary structure 3 15 Side chain interactions contributing to tertiary structure Mistake in text Ionic bond Hydrogen bond Hydrophobic Interactions Hydrophobic interaction Hydrogen bond Polypeptide backbone Disulfide bond Ionic bond Disulfide bridge http www dynamicscience com au tester solutions1 chemistry foodchemistry proteins1 htm Quaternary structure 3 13 and 3 14 Quaternary 4 structure the overall protein structure resulting from interaction between two or more polypeptides subunits Heme group Beta chains Alpha chains Hemoglobin Motifs and Domains 3 16 Motif small regions in different proteins with common structural features Domain discrete functional unit of a protein Most proteins have multiple domains Domain 1 Helix turn Helix motif Domain 3 Domain 2 Effects of chemical and physical conditions on protein structure Tertiary structure overall shape depends on chemical and physical conditions as well as amino acid sequence Denaturation unraveling of a protein loss of tertiary structure Denaturation High or low pH High temperature Nonpolar solvents Properly folded protein Denatured protein Renaturation refolding In cells protein folding and refolding is assisted by chaperone proteins proteins that assist in the proper folding of other proteins Fig 3 17 Effects of chemical and physical conditions on protein structure Effect of pH H Ionic bond Low pH High H Neutral pH High pH Low H 2 Effect of mutations on protein structure and function Light body Dark points extremities Due to a mutation in gene coding for tyrosinase an enzyme required for synthesis of melanin dark pigment Enzyme more sensitive to elevated temperature Extremities cool Active enzyme melanin produced Torso warm tyrosinase Enzyme denatured no melanin Mutations and protein structure 13 15 Mutations affecting primary structure often affect other levels of structure Example sickle cell anemia a mutation in hemoglobin Primary structure Normal hemoglobin Val His Leu Thr Pro Glu Secondary and Tertiary structures b subunit Sickle cell hemoglobin Val His Quaternary structure Leu a Pro Val Glu b subunit a Sickle cell hemoglobin Thr Exposed hydrophobic region a Normal cell Glu a Sickle cell Lipids slides 20 26 Lipids do not form polymers highly diverse in form and function unifying feature have little or no affinity for water insoluble in water composed mostly of hydrocarbons which form nonpolar covalent bonds few polar groups to make them soluble in water mostly hydrophobic most biologically important lipids fats phospholipids and steroids terpenes Triacylglycerol 3 25 Fats Triacylglycerol Major function energy storage Constructed from glycerol and fatty acids Fatty acid Fatty acid tails can be saturated or unsaturated Triacylglycerol Triglyceride Glycerol Saturated fats Fats made from saturated fatty acids are saturated fats are solid at room temperature because fatty acid tails pack tightly may contribute to cardiovascular disease through plaque deposits include most animal fats 3 25a Unsaturated fats 3 25b Fats made from unsaturated fatty acids are unsaturated fats are liquid at room temperature because fatty acid tails are kinked are also called oils include most fats oils from plants and fish https www youtube com watch v ESPNqKUluRs Phospholipid structure 3 27 Phospholipids major component of cell membranes Nonpolar Hydrophobic Polar Hydrophilic Tails Head Groups glycerol backbone two fatty acid tails one phosphate group Amphipathic part hydrophilic and part hydrophobic partly having an affinity for water and partly not Phospholipid bilayer in water 3 28b Phospholipids in water will self assemble into a bilayer Hydrophilic head Hydrophobic tails Lowest energy state Basis of membrane formation in cells Steroids 3 26 Steroids lipids having a carbon skeleton consisting of four fused rings a component of cell membranes especially in animals precursor of steroid hormones Macromolecules Summary Table Table 3 1 Learning Objectives You should be able to also see study guide 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Explain how carbon s electron configuration relates to its ability to form the huge diversity of organic molecules found in living systems Describe how carbon skeletons may vary and explain how this variation contributes to the diversity and complexity of organic molecules Name the major functional groups found in organic molecules