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This chapter provides an overview of macromolecules and their structures, focusing on polymers and their monomers. It covers the diversity of polymers and the synthesis and breakdown processes. The chapter also discusses the role of carbohydrates as fuel and building material, including monosaccharides, disaccharides, and polysaccharides. The structures of starch, glycogen, and cellulose are examined in detail.
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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 • Are complex in their structures
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
A polymer • Is a long molecule consisting of many similar building blocks called monomers
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 reactions
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
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
Concept 5.2: Carbohydrates serve as fuel and building material • Carbohydrates • Include both sugars and their polymers
Sugars • Monosaccharides • Are the simplest sugars • Can be used for fuel • Can be converted into other organic molecules • Can be combined into polymers
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
O H 1 C 6CH2OH 6CH2OH 2 CH2OH H C OH 5C H 5C O O 6 3 H O H H H H H 5 HO C H HOH H HOH 4 4C 1 C 1C 4C 4 1 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 (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. Figure 5.4 • Monosaccharides • May be linear • Can form rings
Disaccharides • Consist of two monosaccharides • Are joined by a glycosidic linkage
(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
Polysaccharides • Polysaccharides • Are polymers of sugars • Serve many roles in organisms
Storage Polysaccharides • Starch • Is a polymer consisting entirely of glucose monomers
Chloroplast Starch 1 m Amylose Amylopectin (a) Starch: a plant polysaccharide Figure 5.6 • Is the major storage form of glucose in plants
Giycogen granules Mitochondria 0.5 m Glycogen Figure 5.6 (b) Glycogen: an animal polysaccharide • Glycogen • Consists of glucose monomers • Is the major storage form of glucose in animals
Structural Polysaccharides • Cellulose • Is a polymer of glucose
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
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
Figure 5.9 • Cellulose is difficult to digest • Cows have microbes in their stomachs to facilitate this process
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
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
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 • Fats • Are constructed from two types of smaller molecules, a single glycerol and usually three fatty acids H H H H H H H H O H H H H H H H H Figure 5.11 (b) Fat molecule (triacylglycerol)
Fatty acids • Vary in the length and number and locations of double bonds they contain
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
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
Phospholipids • Phospholipids • Have only two fatty acids • Have a phosphate group instead of a third fatty acid
+ 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”
WATER Hydrophilic head WATER Hydrophobic tail Figure 5.14 • The structure of phospholipids • Results in a bilayer arrangement found in cell membranes
Steroids • Steroids • Are lipids characterized by a carbon skeleton consisting of four fused rings
H3C CH3 CH3 CH3 CH3 HO Figure 5.15 • One steroid, cholesterol • Is found in cell membranes • Is a precursor for some hormones
Concept 5.4: Proteins have many structures, resulting in a wide range of functions • Proteins • Have many roles inside the cell
Table 5.1 • An overview of protein functions
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
Polypeptides • Polypeptides • Are polymers of amino acids • A protein • Consists of one or more polypeptides
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
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
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)
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
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
Protein Conformation and Function • A protein’s specific conformation • Determines how it functions
Groove (a) A ribbon model Groove (b) A space-filling model Figure 5.19 • Two models of protein conformation
+H3NAmino end Pro Thr Gly Gly Amino acid subunits Thr 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 o Thr – Pro Asn Carboxyl end Figure 5.20 Four Levels of Protein Structure • Primary structure • Is the unique sequence of amino acids in a polypeptide
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
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
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
+H3N Amino end Amino acid subunits helix • The four levels of protein structure