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Chapter 5

Chapter 5. The Structure and Function of Macromolecules. Overview: The Molecules of Life Another level in the hierarchy of biological organization is reached when small organic molecules are joined together. Figure 5.1. Macromolecules Are large molecules composed of smaller molecules

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Chapter 5

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  1. Chapter 5 The Structure and Function of Macromolecules

  2. Overview: The Molecules of Life • Another level in the hierarchy of biological organization is reached when small organic molecules are joined together

  3. Figure 5.1 • Macromolecules • Are large molecules composed of smaller molecules • Are complex in their structures

  4. Concept 5.1: Most macromolecules are polymers, built from monomers • Three of the classes of life’s organic molecules are polymers • Carbohydrates • Proteins • Nucleic acids • The fourth class is not a polymer (the lipids)

  5. A polymer (poly=many; mer=part) • Is a long molecule consisting of many similar building blocks called monomers (mono=single)

  6. 1 HO H 3 2 H HO Unlinked monomer Short polymer Dehydration removes a watermolecule, forming a new bond H2O 1 2 3 4 HO H Longer polymer (a) Dehydration reaction in the synthesis of a polymer Figure 5.2A The Synthesis and Breakdown of Polymers • Monomers form larger molecules by condensation reactions called dehydration (polymerization)reactions • Requires energy • Requiresenzymes

  7. 1 3 HO 4 2 H Hydrolysis adds a watermolecule, breaking a bond H2O 1 2 H HO 3 H HO (b) Hydrolysis of a polymer Figure 5.2B • Polymers can disassemble by • Hydrolysis: (hydro= water; lysis= break) • Releases energy • Enzymesspeed up hydrolysis

  8. The Diversity of Polymers • Each class of polymer • Is formed from a specific set of monomers 1 3 2 H HO • Although organisms share the same limited number of monomer types, each organism is unique based on the arrangement of monomers into polymers • An immense variety of polymers can be built from a small set of monomers

  9. Concept 5.2: Carbohydrates serve as fuel and building material • Carbohydrates • Include both sugars and their polymers • Monomers of carbohydrates are simple sugars called Monosaccharides • Polymers are formed by condensation reaction • Are classified based on the number of simple sugars

  10. Sugars • Monosaccharides • Mono=single, sacchar=sugar • Are the simple sugars in which C, H and O are occur in the ratio of CH2O. • Are major nutrients for the cell • Can be produced by photosynthesis from CO2, H2O and sunlight. • Store energy in their chemical bonds which are harvested by cellular respiration. • Can be incorporated as monomers into disaccharides and polysaccharides

  11. Triose sugars(C3H6O3) Pentose sugars(C5H10O5) Hexose sugars(C6H12O6) H H H H O O O O C C C C H C OH H C OH H C OH H C OH H C OH H C OH HO C H HO C H Aldoses H H C OH H C OH HO C H H C OH H C OH H C OH Glyceraldehyde H C OH H C OH H Ribose H H Glucose Galactose H H H H C OH H C OH H C OH C O C O C O HO C H H C OH H C OH Ketoses H C OH H C OH H Dihydroxyacetone H C OH H C OH H C OH H Ribulose H Figure 5.3 Fructose • Examples of monosaccharides

  12. O H 1 C 6CH2OH 6CH2OH 2 CH2OH H C OH 5C H 5C O O 6 3 O H H H H H H 5 HO C H H HOH HOH 4 4C 1 C 1C 4C 1 4 OH H H H C OH O HO OH 3 2 OH OH 5 OH 2 C C 3 C 2C 3 OH H C H OH 6 H H OH OH H C OH H Figure 5.4 (a) Linear and ring forms. Chemical equilibrium between the linear and ring structures greatly favors the formation of rings. To form the glucose ring, carbon 1 bonds to the oxygen attached to carbon 5. • Monosaccharides • May be linear • Can form rings

  13. Disaccharides • (Di=two; sacchar=sugar) • consists of two monosaccharides joined byglycosidic linkage • Maltose (malt sugar) = glucose + glucose • Lactose (milk sugar) = glucose + galactose • Sucrose (table sugar) = glucose + fructose

  14. (a) Dehydration reaction in the synthesis of maltose. The bonding of two glucose units forms maltose. The glycosidic link joins the number 1 carbon of one glucose to the number 4 carbon of the second glucose. Joining the glucose monomers in a different way would result in a different disaccharide. CH2OH CH2OH CH2OH CH2OH O O O O H H H H H H H H 1–4glycosidiclinkage HOH HOH HOH HOH 4 1 H H H H OH OH O H OH HO HO OH O H H H H OH OH OH OH H2O Glucose Maltose Glucose CH2OH CH2OH CH2OH CH2OH O O O O 1–2glycosidiclinkage H H H H H H HOH HOH 2 1 H H HO H HO H Dehydration reaction in the synthesis of sucrose. Sucrose is a disaccharide formed from glucose and fructose.Notice that fructose,though a hexose like glucose, forms a five-sided ring. (b) OH H O O HO CH2OH HO CH2OH H OH H H OH H OH OH H2O Glucose Sucrose Fructose Figure 5.5 • Examples of disaccharides

  15. Polysaccharides • Polysaccharides • Macromolecules that are polymers of a few hundred or thousand of monosaccharides. • Formed by linking monomers in condensation reaction • Have two important biological functions: i. energy storage (starch and glycogen) ii. structural support (cellulose and chitin).

  16. Storage Polysaccharides • Starch • Is a polymer consisting entirely of glucose monomers

  17. Chloroplast Starch 1 m Amylose Amylopectin (a) Starch: a plant polysaccharide Figure 5.6 Starch • Is the major storage form of glucose in plants • Stored as granules within plant organelles called plastids • Amylosethe simplest form is an unbranched polymer. • Amylopectinis branched polymer • Most animals have digestive enzymes to hydrolyse starch

  18. Mitochondria Giycogen granules 0.5 m Glycogen Figure 5.6 (b) Glycogen: an animal polysaccharide Glycogen • Large glucose polymer that is more highly branched than amylopectin • Is the major storage form of glucose in animals • Stored in the muscles and liver of humans and other vertebrates

  19. Structural Polysaccharides • Cellulose • Linear unbranched polymer of glucose • Differ from starch in its glycosidic linkages • Cellulose and starch have different three-dimensional shapes and properties as a result of differences in glycosidic linkages.

  20. H O CH2OH C CH2OH OH H C H O O OH H H H H HO C H 4 4 1 OH H OH H HO OH H HO H C OH H OH OH H C OH H  glucose C  glucose H OH (a)  and  glucose ring structures CH2OH CH2OH CH2OH CH2OH O O O O 1 4 4 4 1 1 1 OH OH OH OH O O O O HO OH OH OH OH (b) Starch: 1– 4 linkage of  glucose monomers CH2OH CH2OH OH OH O O O O OH OH OH OH 4 O 1 HO OH O O CH2OH CH2OH OH OH (c) Cellulose: 1– 4 linkage of  glucose monomers Figure 5.7 A–C • Has different glycosidic linkages than starch

  21. About 80 cellulose molecules associate to form a microfibril, the main architectural unit of the plant cell wall. Cellulose microfibrils in a plant cell wall Microfibril Cell walls  0.5 m Plant cells OH OH CH2OH CH2OH O O O O OH OH OH OH O O O O O OH CH2OH OH CH2OH Cellulose molecules CH2OH OH CH2OH OH O O O O OH OH OH OH Parallel cellulose molecules are held together by hydrogen bonds between hydroxyl groups attached to carbon atoms 3 and 6. O O O O O OH CH2OH OH CH2OH CH2OH CH2OH OH OH O O O O OH OH OH OH O O O A cellulose molecule is an unbranched  glucose polymer. O O OH CH2OH OH CH2OH Figure 5.8 • Glucose monomer • Is a major component of the tough walls that enclose plant cells

  22. Figure 5.9 • Cellulose is difficult to digest • Cows have microbes in their stomachs to facilitate this process

  23. CH2OH O OH H H OH H H H NH O C CH3 OH (b) Chitin forms the exoskeleton of arthropods. This cicada is molting, shedding its old exoskeleton and emerging in adult form. (c) Chitin is used to make a strong and flexible surgical thread that decomposes after the wound or incision heals. (a) The structure of the chitin monomer. Figure 5.10 A–C • Chitin, another important structural polysaccharide • Is found in the exoskeleton of arthropods • Can be used as surgical thread

  24. Concept 5.3: Lipids are a diverse group of hydrophobic molecules • Lipids • Are the one class of large biological molecules that do not consist of polymers • Share the common trait of being hydrophobic

  25. C C C C C C C H C H O H C C C C C C C C C HO H H H H H H H H H H H H H H H H C OH Fatty acid (palmitic acid) H C OH H Glycerol (a) Dehydration reaction in the synthesis of a fat Ester linkage O H H H H H H H H H H H H H H H H H H O C C C C C C C C C C C C C C C C C H H H H H H H H H H H H H H H O H H H H H H H H H H H H H H H O C H C C C C C C C H C C C C C C C C C H H H H H H H H H H H H H H H O H H H H H H H H H H H H H H H H H C O C C C C C C C C C C C C C C C C H H H H H H H H H H H H H H H H Fats • Are constructed from two types of smaller molecules • a single glycerol (a three carbon alcohol) and usually three fatty acids (carboxylic acid) H H H H H H H H O Fats are formed by a condensation reaction which links glycerol to fatty acids by an Ester linkage. H H H H H H H H Figure 5.11 (b) Fat molecule (triacylglycerol)

  26. Fatty acids • composed of a carboxyl group at one end (head) and an attached hydrocarbon (C-H) chain (tail) • Nonpolar C-H bonds make the chain hydrophobic (not water soluble) • Vary in the length and number and locations of double bonds they contain

  27. Stearic acid Figure 5.12 (a) Saturated fat and fatty acid • Saturated fatty acids • Have the maximum number of hydrogen atoms possible • Have no double bonds

  28. Oleic acid cis double bond causes bending Figure 5.12 (b) Unsaturated fat and fatty acid • Unsaturated fatty acids • Have one or more double bonds

  29. Phospholipids • Phospholipids • Have only two fatty acids • Have a phosphate group instead of a third fatty acid

  30. + CH2 Choline N(CH3)3 CH2 O Phosphate Hydrophilic head – P O O O CH2 CH CH2 Glycerol O O C O C O Fatty acids Hydrophilic head Hydrophobic tails Hydrophobic tails (c) Phospholipid symbol (b) Space-filling model Figure 5.13 (a) Structural formula • Phospholipid structure • Consists of a hydrophilic “head” and hydrophobic “tails” → it’s amphiphatic

  31. WATER Hydrophilic head WATER Hydrophobic tail Figure 5.14 • The structure of phospholipids • Results in a bilayer arrangement found in cell membranes

  32. Steroids • Steroids • Are lipids characterized by a carbon skeleton consisting of four fused rings

  33. H3C CH3 CH3 CH3 CH3 HO Figure 5.15 • One steroid, cholesterol • Is found in cell membranes • Is a precursor for some hormones

  34. Concept 5.4: Proteins have many structures, resulting in a wide range of functions • Proteins • Have many roles inside the cell

  35. An overview of protein functions - Are abundant, forming about 50% of cellular dry weight - Have important functions in the cell: 1.structural support 2.storage (of amino acids) 3.transport (e.g. hemoglobin) 4. signaling (chemical messengers) 5.cellular response (receptor proteins) 6.movement (contractile proteins) 7.defense (antibodies) 8.catalysts of biochemical reactions (enzymes

  36. Substrate binds to enzyme. 1 Active site is available for a molecule of substrate, the reactant on which the enzyme acts. 2 2 Substrate (sucrose) Glucose Enzyme (sucrase) OH H2O Fructose H O 4 Products are released. 3 Substrate is converted to products. Figure 5.16 • Enzymes • Are a type of protein that acts as a catalyst, speeding up chemical reactions

  37. Polypeptides • Polypeptides • Are polymers of amino acids • A protein • Consists of one or more polypeptides

  38. Amino Acid Monomers • Amino acids • Are organic molecules possessing both carboxyl and amino groups • Differ in their properties due to differing side chains, called R groups

  39. CH3 CH3 CH3 CH CH2 CH3 CH3 H CH3 H3C CH3 CH2 CH O O O O O H3N+ C H3N+ C H3N+ H3N+ C C C C C C H3N+ C C O– O– O– O– O– H H H H H Valine (Val) Leucine (Leu) Isoleucine (Ile) Glycine (Gly) Alanine (Ala) Nonpolar CH3 CH2 S H2C CH2 O NH CH2 C C H2N CH2 CH2 O– CH2 O O O H H3N+ H3N+ C C C C H3N+ C C O– O– O– H H H Phenylalanine (Phe) Proline (Pro) Methionine (Met) Tryptophan (Trp) Figure 5.17 • 20 different amino acids make up proteins

  40. OH NH2 O C NH2 O C OH SH CH2 CH3 OH Polar CH2 CH CH2 CH2 CH2 CH2 O O O O O O H3N+ C H3N+ C H3N+ C C H3N+ C C H3N+ C C C C C H3N+ C O– O– O– O– O– O– H H H H H H Glutamine (Gln) Tyrosine (Tyr) Asparagine (Asn) Cysteine (Cys) Serine (Ser) Threonine (Thr) Basic Acidic NH3+ NH2 NH+ O– O –O O CH2 C NH2+ C C NH Electrically charged CH2 CH2 CH2 CH2 CH2 O O CH2 CH2 C CH2 C H3N+ C H3N+ C O O– O– CH2 C H3N+ CH2 C H O H O– C C H3N+ CH2 H O O– C C H3N+ H O– H Lysine (Lys) Histidine (His) Arginine (Arg) Glutamic acid (Glu) Aspartic acid (Asp)

  41. Peptidebond OH SH CH2 CH2 CH2 H H H C C H C C N C OH H C OH N N DESMOSOMES H O H O H O (a) H2O OH DESMOSOMES DESMOSOMES Side chains SH OH Peptidebond CH2 CH2 CH2 H H H N OH C C C C C H C N N Backbone H H O O H O Amino end(N-terminus) Carboxyl end(C-terminus) Figure 5.18 (b) Amino Acid Polymers • Amino acids • Are linked by peptide bonds OH

  42. Determining the Amino Acid Sequence of a Polypeptide • The amino acid sequences of polypeptides • Were first determined using chemical means • Can now be determined by automated machines

  43. Protein Conformation and Function • A protein’s specific conformation • Determines how it functions

  44. Groove (a) A ribbon model Groove (b) A space-filling model Figure 5.19 • Two models of protein conformation

  45. Pro Thr Gly Gly Thr Amino acid subunits +H3NAmino end Gly Glu Seu Lys Cys Pro Leu Met Val Lys Val Leu Asp Ala Arg Val Gly Ser Pro Ala Glu Lle Asp Thr Lys Ser Tyr Trp Lys Ala Leu Gly lle Ser Pro Phe His Glu His Ala Glu Val Thr Phe Val Ala Asn lle Thr Asp Ala Tyr Arg Ser Ala Arg Pro Gly Leu Leu Ser Pro Tyr Ser Tyr Ser Thr Thr Ala o Val c Val Glu Lys – Thr o Pro Asn Carboxyl end Figure 5.20 Four Levels of Protein Structure • Primary structure • Is the unique sequence of amino acids in a polypeptide • determined by genes • slight change can effect the protein conformation and function (e.g. sickle-cell hemoglobin)

  46. Normal hemoglobin Sickle-cell hemoglobin Primary structure Primary structure . . . . . . Exposed hydrophobic region Val His Leu Thr Pro Glul Glu Val His Leu Pro Glu Thr Val 5 6 7 3 4 5 6 7 1 2 1 2 3 4 Secondaryand tertiarystructures Secondaryand tertiarystructures  subunit  subunit     Quaternary structure Hemoglobin A Quaternary structure Hemoglobin S     Molecules interact with one another tocrystallize into a fiber, capacity to carry oxygen is greatly reduced. Function Molecules donot associatewith oneanother, eachcarries oxygen. Function 10 m 10 m Normal cells arefull of individualhemoglobinmolecules, eachcarrying oxygen Red bloodcell shape Red bloodcell shape Figure 5.21 • Hemoglobin structure and sickle-cell disease Fibers of abnormalhemoglobin deform cell into sickle shape.

  47. H H H H H H O O O O O O O H H H H H H R R R R R R R C C C C C C C C C C C C C N N N N N N N N N N N N N C C C C C C C C C C C C C C R R R R R R H H H H H H H O O O O O O O H H H H H H H  pleated sheet H O H H Amino acidsubunits C C N N N C C C R H O H H H H H H N N N N N N  helix C C O C H H H C C C R R R R R H H C C C C C C O O O O H C R O C C O H C O N N H C C H R H R Figure 5.20 • Secondary structure • Is the folding or coiling of the polypeptide into a repeating configuration • Includes the  helix and the  pleated sheet • Stabilized by hydrogen bonding

  48. Hydrophobic interactions and van der Waalsinteractions CH CH2 CH2 H3C CH3 OH Polypeptidebackbone H3C CH3 Hyrdogenbond CH O HO C CH2 CH2 S S CH2 Disulfide bridge O -O C CH2 CH2 NH3+ Ionic bond • Tertiary structure • Is the overall three-dimensional shape of a polypeptide • Results from interactions between amino acids and R groups covalent Non-covalent

  49. Polypeptidechain Collagen  Chains Iron Heme  Chains Hemoglobin • Quaternary structure • Is the overall protein structure that results from the aggregation of two or more polypeptide subunits

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