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The Structure and Function of Macromolecules: Overview of the Molecules of Life

This chapter provides an overview of the structure and function of macromolecules in living organisms. It discusses the synthesis and breakdown of polymers, the role of carbohydrates as fuel and building materials, the diverse group of lipids, and the many structures and functions of proteins.

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The Structure and Function of Macromolecules: Overview of the Molecules of Life

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  1. Chapter 5 The Structure and Function of Macromolecules

  2. Overview: The Molecules of Life • Macromolecules are large molecules composed of thousands of covalently connected atoms

  3. Concept 5.1: Most macromolecules are polymers, built from monomers • A polymer is a long molecule consisting of many similar building blocks called monomers • Three of the four classes of life’s organic molecules are polymers: • Carbohydrates • Proteins • Nucleic acids

  4. The Synthesis and Breakdown of Polymers • Dehydration synthesis • Hydrolysis Short polymer Unlinked monomer Dehydration removes a water molecule, forming a new bond Longer polymer Dehydration reaction in the synthesis of a polymer Hydrolysis adds a water molecule, breaking a bond Animation: Polymers Hydrolysis of a polymer

  5. Dehydration Synthesis and Hydrolysis

  6. Concept 5.2: Carbohydrates serve as fuel and building material • Carbohydrates include sugars and the polymers of sugars • Monosaccharides • Disaccharides • Polysaccharides

  7. Sugars • Monosaccharides have molecular formulas that are usually multiples of CH2O • Glucose is the most common monosaccharide

  8. LE 5-3 Triose sugars (C3H6O3) Pentosesugars (C5H10O5) Hexose sugars (C5H12O6) Aldoses Glyceraldehyde Ribose Galactose Glucose Ketoses Dihydroxyacetone Ribulose Fructose

  9. Monosaccharides serve as a major fuel for cells and as raw material for building molecules • in aqueous solutions they form rings Linear and ring forms Abbreviated ring structure

  10. A disaccharide is formed when a dehydration reaction joins two monosaccharides • glycosidic linkage Animation: Disaccharides

  11. LE 5-5 Dehydration reaction in the synthesis of maltose 1–4 glycosidic linkage Glucose Glucose Maltose Dehydration reaction in the synthesis of sucrose 1–2 glycosidic linkage Sucrose Fructose Glucose

  12. Polysaccharides • Polysaccharides, the polymers of sugars, have storage and structural roles

  13. Storage Polysaccharides Chloroplast Starch • Starch, a storage polysaccharide of plants, consists entirely of glucose monomers 1 µm Amylose Amylopectin Starch: a plant polysaccharide

  14. Glycogen granules Mitochondria • Glycogen is a storage polysaccharide in animals 0.5 µm Glycogen Glycogen: an animal polysaccharide

  15. Structural Polysaccharides • Cellulose is a major component of the tough wall of plant cells • glycosidic linkages differ from starch • The difference is based on two ring forms for glucose: alpha () and beta () Animation: Polysaccharides

  16. LE 5-7 a Glucose b Glucose a and b glucose ring structures Starch: 1–4 linkage of a glucose monomers. Cellulose: 1–4 linkage of b glucose monomers.

  17. LE 5-8 Cellulose microfibrils in a plant cell wall Cell walls Microfibril 0.5 µm Plant cells Cellulose molecules b Glucose monomer

  18. Enzymes that digest starch by hydrolyzing alpha linkages can’t hydrolyze beta linkages in cellulose

  19. Chitin • exoskeleton of arthropods • cell walls of many fungi • Chitin can be used as surgical thread

  20. Concept 5.3: Lipids are a diverse group of hydrophobic molecules • Lipids are the one class of large biological molecules that do not form polymers • no affinity for water (hydrophobic) • Fats • Phospholipids • Steroids

  21. Fats • Fats • constructed from: • Glycerol • Fatty acids Animation: Fats

  22. LE 5-11a Fatty acid (palmitic acid) Glycerol Dehydration reaction in the synthesis of a fat

  23. Ester linkage • In a fat, three fatty acids are joined to glycerol by an ester linkage, creating a triacylglycerol, or triglyceride Fat molecule (triacylglycerol)

  24. Saturated fatty acids • Unsaturated fatty acids

  25. Saturated fats • Most animal fats are saturated (except fish) • solid at room temperature • may contribute to cardiovascular disease through plaque deposits Stearic acid Saturated fat and fatty acid.

  26. Unsaturated fats • Plant fats and fish fats • liquid at room temperature and are called oils Oleic acid cis double bond causes bending Unsaturated fat and fatty acid.

  27. Phospholipids • Phospholipid • two fatty acids and a phosphate group • attached to glycerol • Fatty acid tails are hydrophobic • Phosphate group are hydrophilic

  28. LE 5-13 Choline Hydrophilic head Phosphate Glycerol Hydrophobic tails Fatty acids Hydrophilic head Hydrophobic tails Space-filling model Structural formula Phospholipid symbol

  29. Phospholipids self-assemble into a bilayer WATER Hydrophilic head Hydrophobic tails WATER

  30. Steroids • Steroids are lipids characterized by a carbon skeleton consisting of four fused rings • Cholesterol, an important steroid, is a component in animal cell membranes

  31. Concept 5.4: Proteins have many structures, resulting in a wide range of functions • Proteins account for more than 50% of the dry mass of most cells • Functions include: • Structural support • Storage • Transport • Cellular communications • Movement • Defense against foreign substances

  32. Animation: Structural Proteins Animation: Storage Proteins Animation: Transport Proteins Animation: Receptor Proteins Animation: Contractile Proteins Animation: Defensive Proteins Animation: Enzymes Animation: Hormonal Proteins Animation: Sensory Proteins Animation: Gene Regulatory Proteins

  33. Enzymes acts as a catalyst, speeding up chemical reactions • Enzymes can perform their functions repeatedly Substrate (sucrose) Glucose Enzyme (sucrose) Fructose

  34. Amino Acid Monomers a carbon • Amino acids • differ in their properties due to differing side chains, called R groups • Cells use 20 amino acids to make thousands of proteins Carboxyl group Amino group

  35. LE 5-17a Alanine (Ala) Valine (Val) Isoleucine (Ile) Glycine (Gly) Leucine (Leu) Nonpolar Methionine (Met) Phenylalanine (Phe) Proline (Pro) Tryptophan (Trp)

  36. LE 5-17b Polar Tyrosine (Tyr) Serine (Ser) Asparagine (Asn) Threonine (Thr) Cysteine (Cys) Glutamine (Gln)

  37. LE 5-17c Acidic Basic Electrically charged Aspartic acid (Asp) Lysine (Lys) Arginine (Arg) Glutamic acid (Glu) Histidine (His)

  38. Amino Acid Polymers • Amino acids are linked by peptide bonds • A polypeptide is a polymer of amino acids

  39. Protein Conformation and Function • Functional protein • one or more polypeptides twisted, folded, and coiled into a unique shape • conformation determines function Groove Groove A ribbon model Groove Groove A space-filling model

  40. Four Levels of Protein Structure • Primary structure • unique sequence of amino acids • Secondary structure • coils and folds in the polypeptide chain (H bonds) • Tertiary structure • interactions among various R groups (various bonds) • Quaternary structure • protein consists of multiple polypeptide chains Animation: Protein Structure Introduction

  41. LE 5-20 b pleated sheet +H3N Amino end Amino acid subunits  helix

  42. LE 5-20a Amino end Amino acid subunits Animation: Primary Protein Structure Carboxyl end

  43. LE 5-20b b pleated sheet Amino acid subunits  helix Animation: Secondary Protein Structure

  44. LE 5-20d Hydrophobic interactions and van der Waals interactions Polypeptide backbone Hydrogen bond Disulfide bridge Animation: Tertiary Protein Structure Ionic bond

  45. LE 5-20e Polypeptide chain b Chains Iron Heme a Chains Hemoglobin Polypeptide chain Collagen Animation: Quaternary Protein Structure

  46. Sickle-Cell Disease: A Simple Change in Primary Structure • A slight change in primary structure can affect a protein’s conformation and ability to function • Sickle-cell disease • results from a single amino acid substitution in the protein hemoglobin 10 µm 10 µm Red blood cell shape Fibers of abnormal hemoglobin deform cell into sickle shape. Red blood cell shape Normal cells are full of individual hemoglobin molecules, each carrying oxygen.

  47. LE 5-21b Sickle-cell hemoglobin Normal hemoglobin Primary structure Primary structure Val Val His His Thr Pro Glu Glu Thr Pro Val Glu Leu Leu 1 1 2 4 6 2 4 6 7 7 3 5 3 5 Exposed hydrophobic region Secondary and tertiary structures Secondary and tertiary structures b subunit b subunit a  a  Quaternary structure Sickle-cell hemoglobin Normal hemoglobin (top view) Quaternary structure a   a Function Molecules do not associate with one another; each carries oxygen. Molecules interact with one another to crystallize into a fiber; capacity to carry oxygen is greatly reduced. Function

  48. What Determines Protein Conformation? • In addition to primary structure, physical and chemical conditions can affect conformation • Alternations in pH • Salt concentration • Temperature • This loss of a protein’s native conformation is called denaturation

  49. LE 5-22 Denaturation Normal protein Denatured protein Renaturation

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