1 Chapter 5 The Structure and Function of Macromolecules

2 The Molecules of Life Overview: –Another level in the hierarchy of biological organization is reached when small organic molecules are joined together –Atom ---> molecule ---  compound

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

4 Macromolecules Most macromolecules are polymers, built from monomers Four classes of life’s organic molecules are polymers –Carbohydrates –Proteins –Nucleic acids –Lipids

5 A polymer –Is a long molecule consisting of many similar building blocks called monomers –Specific monomers make up each macromolecule –E.g. amino acids are the monomers for proteins

6 The Synthesis and Breakdown of Polymers Monomers form larger molecules by condensation reactions called dehydration synthesis (a) Dehydration reaction in the synthesis of a polymer HOH H H H2OH2O Short polymer Unlinked monomer Longer polymer Dehydration removes a water molecule, forming a new bond Figure 5.2A

7 The Synthesis and Breakdown of Polymers Polymers can disassemble by –Hydrolysis (addition of water molecules) (b) Hydrolysis of a polymer HO H H H2OH2O H Hydrolysis adds a water molecule, breaking a bond Figure 5.2B

8 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 Carbohydrates Serve as fuel and building material Include both sugars and their polymers (starch, cellulose, etc.)

10 Sugars Monosaccharides –Are the simplest sugars –Can be used for fuel –Can be converted into other organic molecules –Can be combined into polymers

11 Examples of monosaccharides Triose sugars (C 3 H 6 O 3 ) Pentose sugars (C 5 H 10 O 5 ) Hexose sugars (C 6 H 12 O 6 ) H C OH HO C H H C OH HO C H H C OH C O H C OH HO C H H C OH C O H H H HHH H H HHH H H H C CCC O O O O Aldoses Glyceraldehyde Ribose Glucose Galactose Dihydroxyacetone Ribulose Ketoses Fructose Figure 5.3 *What functional groups are present in all sugars?

12 Monosaccharides –May be linear –Can form rings H H C OH HO C H H C OH H C O C H H OH 4C4C 6 CH 2 OH 5C5C H OH C H OH H 2 C 1C1C H O H OH 4C4C 5C5C 3 C H H OH OH H 2C2C 1 C OH H CH 2 OH H H OH HO H 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. OH 3 O H O O 6 1 Figure 5.4

13 Disaccharides –Consist of two monosaccharides –Are joined by a glycosidic linkage

14 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. 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. (a) (b) H HO H H OH H OH O H CH 2 OH H HOHO H HOHHOH H OHOH O H OHOH H O H H OH H OH O H CH 2 OH H H2OH2O H2OH2O H H O H HO H OH O H CH 2 OH HO OH H CH 2 OH HOHHOH H H HO OH H CH 2 OH HOHHOH H O O H OH H CH 2 OH HOHHOH H O H OH CH 2 OH H HO O CH 2 OH H H OH O O – 4 glycosidic linkage 1–2 glycosidic linkage Glucose Fructose Maltose Sucrose OH H H Figure 5.5

15 Polysaccharides –Are polymers of sugars –Serve many roles in organisms

16 Storage Polysaccharides Starch –Is a polymer consisting entirely of glucose monomers –Is the major storage form of glucose in plants Chloroplast Starch Amylose Amylopectin 1  m (a) Starch: a plant polysaccharide Figure 5.6

17 Glycogen –Consists of glucose monomers –Is the major storage form of glucose in animals Mitochondria Giycogen granules 0.5  m (b) Glycogen: an animal polysaccharide Glycogen Figure 5.6

18 Cellulose –Is a polymer of glucose –Has different glycosidic linkages than starch (c) Cellulose: 1– 4 linkage of  glucose monomers H O O CH 2 O H H OHOH H H OHOH OHOH H H HOHO 4 C C C C C C H H H HOHO OHOH H OHOH OHOH OHOH H O H H H OHOH OHOH H H HOHO 4 OHOH O OHOH OHOH HOHO 4 1 O O OHOH OHOH O O OHOH OHOH O OHOH OHOH O O O OHOH OHOH HOHO 4 O 1 OHOH O OHOH OHOH O O OHOH O OHOH O OHOH OHOH (a)  and  glucose ring structures (b) Starch: 1– 4 linkage of  glucose monomers 1  glucose  glucose CH 2 O H Figure 5.7 A–C

19 Plant cells 0.5  m Cell walls Cellulose microfibrils in a plant cell wall  Microfibril CH 2 OH OH OHOH O O O CH 2 OH O O OH O CH 2 OH OH O O CH 2 OH O O OHOH O O OHOH O O OH CH 2 OHOH O O CH 2 OH OH O CH 2 OH O O OHCH 2 OH OH  Glucose monomer O O O O O O Parallel cellulose molecules are held together by hydrogen bonds between hydroxyl groups attached to carbon atoms 3 and 6. About 80 cellulose molecules associate to form a microfibril, the main architectural unit of the plant cell wall. A cellulose molecule is an unbranched  glucose polymer. OH O O Cellulose molecules Figure 5.8 –Is a major component of the tough walls that enclose plant cells

20 Cellulose is difficult to digest –Cows have microbes in their stomachs to facilitate this process Figure 5.9

21 Chitin, another important structural polysaccharide –Is found in the exoskeleton of arthropods –Can be used as surgical thread (a) The structure of the chitin monomer. O CH 2 O H OH H H H NH C CH 3 O H H (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. OH Figure 5.10 A–C

22 Lipids 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

23 Fats –Are constructed from two types of smaller molecules, a single glycerol and usually three fatty acids –Vary in the length and number and locations of double bonds they contain

24 Fats Glycerol = a 3 C alcohol Fatty Acids = Carboxyl Group Carbons Ester Linkage joins Carboxyl Group to Hydrocarbon chain

25 Ester Linkage Carboxyl Glycerol Hydrocarbon Chain, NON POLAR

26 Saturated fatty acids –Have the maximum number of hydrogen atoms possible –Have no double bonds –Solid at room temp. (a) Saturated fat and fatty acid Stearic acid Figure 5.12

27 Unsaturated fatty acids –Have one or more double bonds –Causes “kinks” = prevents closely packing –Liquid at room temp. (b) Unsaturated fat and fatty acid cis double bond causes bending Oleic acid Figure 5.12

28 Phospholipids –Have only two fatty acids –Have a phosphate group instead of a third fatty acid

29 Phospholipid structure –Consists of a hydrophilic “head” and hydrophobic “tails” CH 2 O P O O O CH CH 2 OO C O C O Phosphate Glycerol (a) Structural formula (b) Space-filling model Fatty acids (c) Phospholipid symbol Hydrophobic tails Hydrophilic head Hydrophobic tails – Hydrophilic head CH 2 Choline + Figure 5.13 N(CH 3 ) 3

30 The structure of phospholipids –Results in a bilayer arrangement found in cell membranes Hydrophilic head WATER Hydrophobic tail Figure 5.14

31 Steroids –Are lipids characterized by a carbon skeleton consisting of four fused rings

32 One steroid, cholesterol –Is found in cell membranes –Is a precursor for some hormones HO CH 3 H3CH3C Figure 5.15

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34 Proteins Proteins have many structures, resulting in a wide range of functions Proteins do most of the work in cells and act as enzymes Proteins are made of monomers called amino acids

35 An overview of protein functions Table 5.1

36 Enzymes –Are a type of protein that acts as a catalyst, speeding up chemical reactions Substrate (sucrose) Enzyme (sucrase) Glucose OH H O H2OH2O Fructose 3 Substrate is converted to products. 1 Active site is available for a molecule of substrate, the reactant on which the enzyme acts. Substrate binds to enzyme Products are released. Figure 5.16 Hydrolysis

37 Polypeptides –Are polymers (chains) of amino acids A protein –Consists of one or more polypeptides

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

39 Twenty Amino Acids 20 different amino acids make up proteins O O–O– H H3N+H3N+ C C O O–O– H CH 3 H3N+H3N+ C H C O O–O– C C O O–O– H H3N+H3N+ CH CH 3 CH 2 C H H3N+H3N+ CH 3 CH 2 CH C H H3N+H3N+ C CH 3 CH 2 C H3N+H3N+ H C O O–O– C H3N+H3N+ H C O O–O– NH H C O O–O– H3N+H3N+ C CH 2 H2CH2C H2NH2N C H C Nonpolar Glycine (Gly) Alanine (Ala) Valine (Val)Leucine (Leu)Isoleucine (Ile) Methionine (Met) Phenylalanine (Phe) C O O–O– Tryptophan (Trp) Proline (Pro) H3CH3C Figure 5.17 S O O–O–

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41 Amino Acid Polymers Amino acids –Are linked by peptide bonds –Dehydration Rxn

42 Protein Conformation and Function A protein’s specific conformation (shape) determines how it functions

43 Four Levels of Protein Structure Primary structure –Is the unique sequence of amino acids in a polypeptide Figure 5.20 – Amino acid subunits + H 3 N Amino end o Carboxyl end o c Gly ProThr Gly Thr Gly Glu Seu Lys Cys Pro Leu Met Val Lys Val Leu Asp Ala Val Arg Gly Ser Pro Ala Gly lle Ser Pro Phe His Glu His Ala Glu Val Phe Thr Ala Asn Asp Ser Gly Pro Arg Tyr Thr lle Ala Leu Ser Pro Tyr Ser Tyr Ser Thr Ala Val Thr Asn Pro Lys Glu Thr Lys Ser Tyr Trp Lys Ala Leu Glu Lle Asp

44 Secondary structure –Is the folding or coiling of the polypeptide into a repeating configuration –Includes the  helix (spiral) and the  pleated sheet (parallel) – hydrogen bonds! H H Figure 5.20

45 Tertiary structure –Is the overall three-dimensional shape of a polypeptide –Results from interactions between amino acids and R groups CH 2 CH OHOH O C HO CH 2 NH 3 + C -O-O CH 2 O SS CH CH 3 H3CH3C H3CH3C Hydrophobic interactions and van der Waals interactions Polypeptide backbone Hyrdogen bond Ionic bond CH 2 Disulfide bridge

46 Quaternary structure –Is the overall protein structure that results from the aggregation of two or more polypeptide subunits Polypeptide chain Collagen  Chains  Chains Hemoglobin Iron Heme

47 Review of Protein Structure + H 3 N Amino end Amino acid subunits  helix

48 Sickle-Cell Disease: A Simple Change in Primary Structure Sickle-cell disease –Results from a single amino acid substitution in the protein hemoglobin

49 Fibers of abnormal hemoglobin deform cell into sickle shape. Primary structure Secondary and tertiary structures Quaternary structure Function Red blood cell shape Hemoglobin A Molecules do not associate with one another, each carries oxygen. Normal cells are full of individual hemoglobin molecules, each carrying oxygen     10  m     Primary structure Secondary and tertiary structures Quaternary structure Function Red blood cell shape Hemoglobin S Molecules interact with one another to crystallize into a fiber, capacity to carry oxygen is greatly reduced.  subunit Normal hemoglobin Sickle-cell hemoglobin... Figure 5.21 Exposed hydrophobic region ValThrHisLeuProGlulGluValHisLeu Thr Pro Val Glu

50 What Determines Protein Conformation? Protein conformation Depends on the physical and chemical conditions of the protein’s environment Temperature, pH, etc. affect protein structure

51 Denaturation is when a protein unravels and loses its native conformation (shape). Disrupts Tertiary structure. Denaturation Renaturation Denatured proteinNormal protein Figure 5.22

52 The Protein-Folding Problem Most proteins –Probably go through several intermediate states on their way to a stable conformation –Denaturated proteins no longer work in their unfolded condition –Proteins may be denaturated by extreme changes in pH or temperature

53 Chaperonins –Are protein molecules that assist in the proper folding of other proteins Hollow cylinder Cap Chaperonin (fully assembled) Steps of Chaperonin Action: An unfolded poly- peptide enters the cylinder from one end. The cap attaches, causing the cylinder to change shape in such a way that it creates a hydrophilic environment for the folding of the polypeptide. The cap comes off, and the properly folded protein is released. Correctly folded protein Polypeptide Figure 5.23

54 Nucleic Acids Nucleic acids store and transmit hereditary information Genes –Are the units of inheritance –Program the amino acid sequence of polypeptides –Are made of nucleotide sequences on DNA

55 The Roles of Nucleic Acids There are two types of nucleic acids –Deoxyribonucleic acid (DNA) –Ribonucleic acid (RNA)

56 Deoxyribonucleic Acid DNA –Stores information for the synthesis of specific proteins –Found in the nucleus of cells

57 DNA Functions –Directs RNA synthesis (transcription) –Directs protein synthesis through RNA (translation) Synthesis of mRNA in the nucleus Movement of mRNA into cytoplasm via nuclear pore Synthesis of protein NUCLEUS CYTOPLASM DNA mRNA Ribosome Amino acids Polypeptide mRNA Figure 5.25

58 Each nucleic acid –Consists of monomers called nucleotides –Sugar + phosphate + nitrogen base Nitrogenous base Nucleoside O O OO OO P CH 2 5’C 3’C Phosphate group Pentose sugar (b) Nucleotide Figure 5.26 O

59 Nucleotide Monomers Nucleotide monomers –Pentose (5C) Sugar (either deoxyribose or ribose) –Nitrogenous Base –Phosphate Group (attached to sugar) (c) Nucleoside components Figure 5.26 CH Uracil (in RNA) U Ribose (in RNA) Nitrogenous bases Pyrimidines C N N C O H NH 2 CH O C N H HN C O C CH 3 N HN C C H O O Cytosine C Thymine (in DNA) T N HC N C C N C CH N NH 2 O N HC N H H C C N NH C NH 2 Adenine A Guanine G Purines O HOCH 2 H H H OH H O HOCH 2 H H H OH H Pentose sugars Deoxyribose (in DNA) Ribose (in RNA) OH CH Uracil (in RNA) U 4’ 5”5” 3’ OH H 2’ 1’ 5”5” 4’ 3’ 2’ 1’

Nitrogenous Bases Purines = 2 Rings, Adenine + Guanine Pyrimidines = 1 ring, Thymine + Cytosine 60

Sugars are bonded to phosphate groups 3’ End = sugar 5 ‘ End = Phosphate Bases in center joined by H bonds 61

62 The DNA double helix –Consists of two antiparallel nucleotide strands 3’ end Sugar-phosphate backbone Base pair (joined by hydrogen bonding) Old strands Nucleotide about to be added to a new strand A 3’ end 5’ end New strands 3’ end 5’ end Figure 5.27

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