Chapter 5 Structure and Function of Large Biological Molecules

1. Chapter 5Structure and Function of Large Biological Molecules

2. What are the Molecules of Life? • Because life is so complex, we would assume that there are numbers of molecules • This is not the case • The large molecules of all living things fall into four main clases • Carbohydrates • Lipids • Proteins • Nucleic acids

3. What are macromolecules? • Huge • Molecules that are very large and complex • Exhibit unique emergent properties due to the orderly arrangement of their atoms

4. What are polymers? • Chain-like molecules • Long molecule consisting of many similar or identical building blocks linked by covalent bonds • Macromolecules in three of the four classes of life’s organic compounds • Carbohydrates • Proteins • Nucleic acids

5. What are monomers? • Repeating units that serve as the building blocks of a polymer • Smaller molecules

6. What’s different about the polymers? • Classes of polymers differ in the nature of their monomers

7. What’s similar about the polymers? • The chemical mechanisms by which cells make and break down polymers are basically the same in all cases

8. What is a condensation reaction? • Monomers are connected by this type of reaction • Two molecules are covalently bonded to each other through loss of a water molecule

9. What is a dehydration reaction? • A specific condensation reaction • Because water is the molecule that is lost • When a bond forms between two monomers, each monomer contributes part of the water molecule that is lost • One molecule provides a hydroxyl group (-OH) • The other provides a hydrogen (- H) • Reaction can be repeated as monomers are added to the chain one by one, making a polymer • Facilitated by enzymes • Specialized macromolecules that speed up chemical reactions in cells

10. What is hydrolysis? • Polymers are disassembled to monomers through this process • Reverse of dehydration reaction • Means “to break using water” • Bonds between the monomers are broken by the addition of water molecules • Hydrogen from water attaching to one monomer • Hydroxyl group attaching to the adjacent monomer

11. What is an example of hydrolysis? • Digestion

12. Short polymer Unlinked monomer Dehydration removes a water molecule, forming a new bond Dehydration and HydrolysisReactions Longer polymer Dehydration reaction in the synthesis of a polymer Hydrolysis adds a water molecule, breaking a bond Hydrolysis of a polymer

13. Dehydration reaction in the synthesis of maltose 1–4 glycosidic linkage Dehydration reactions in Carbohydrates Glucose Glucose Maltose Dehydration reaction in the synthesis of sucrose 1–2 glycosidic linkage Sucrose Fructose Glucose

14. There exists great diversity within macromolecules: • Between one cell to another • Even in same organism • Between siblings variations exist • Between unrelated individuals • More and more extensive differences exist

15. What is the basis for this diversity? • Macromolecules are constructed from only 40 to 50 common monomers • Example: • Proteins are built from only 20 kinds of amino acids arranged in chains that are hundreds of amino acids long • SMALL MOLECULES COMMON TO ALL ORGANISMS ARE ORDERED INTO UNIQUE MACROMOLECULES

16. What is a carbohydrate? • Include both sugars and polymers of sugars • Three forms • Monosaccharide • Disaccharide • Polysaccharide

17. What is a monosaccharide? • Simplest of carbohydrates • Known as simple sugars • From Greek monos (meaning single) and sacchar (meaning sugar) • Have molecular formulas that are some multiple of the following unit: • CH2O

18. What is a monosaccharide? • Example: • C6H12O6 • The most common monosaccharide • Of central importance to the chemistry of life • Aldose

19. What is the structure of a sugar? • Has carbonyl group • >C=O • multiple hydroxyl groups • - OH

20. CarbohydratesSee the Carbonyls and Hydroxides?

21. Dehydration reaction in the synthesis of maltose 1–4 glycosidic linkage Dehydration reactions in Carbohydrates Glucose Glucose Maltose Dehydration reaction in the synthesis of sucrose 1–2 glycosidic linkage Sucrose Fructose Glucose

22. What distinguishes between sugars? • Can be either aldose (aldehyde sugar) or ketose (ketone sugar) • Can also classify sugars by the size of the carbon skeleton • Can also be diversified based on spatial arrangement

23. What distinguishes between sugars? • Can be either aldose (aldehyde sugar) or ketose (ketone sugar) • Glucose is an aldose

24. What distinguishes between sugars? • Can be either aldose (aldehyde sugar) or ketose (ketone sugar) • Can also classify sugars by the size of the carbon skeleton • Ranges from 3 to 7 carbons long • Examples: • Hexoses • Glucose and fructose • Have six carbons • What’s an example of a triose? • What’s an example of a pentose?

25. What distinguishes between sugars? • Can be either aldose (aldehyde sugar) or ketose (ketone sugar) • Can also classify sugars by the size of the carbon skeleton • Can also be diversified based on spatial arrangement • Arrangement around asymmetrical carbon • Example: • Glucose and galactose differ in placement of parts around asymmetrical carbon • This small difference gives those carbons different shapes and behaviors

26. What’s the biological importance of monosaccharides? • In cellular respiration, energy is extracted in series of reactions from glucose • Simple sugars are major source of energy for cells

27. What is a disaccharide? • Double sugars • Consist of two monosaccharides joined by a glycosidic linkage

28. What is glycosidic linkage? • Covalent bond formed between two monosaccharides by dehydration reaction • Example: • Maltose is disaccharide formed by inking of two molecules of glucose • Maltose is also know as a malt sugar • Used in brewing beer • Sucrose • Table sugar • Monomers that make up it are glucose and fructose

29. What is a polysaccharide? • Polymer composed of many sugar building blocks? • Macromolecules • Polymers with few hundred to a few thousand monosaccharides joined by glycosidic linkages • Some serve as storage material that are hydrolyzed as needed to provide sugar for cells

30. What is a storage polysaccharide? • Used for storage for later use • Starch

31. Starch • Plant polysaccharide • Two forms • Amylose (unbranched) • Amylopectin (branched) • Plants store starch as granules within cellular plastids • Include chloroplasts • Polymer of glucose monomers • Allows the buildup (stockpile) of surplus glucose • Represents stored energy • Most glucose monomers are jointed by 1 – 4 linkages • #1 carbon to #4 carbon

32. Starch • Sugar can later be withdrawn from this carbohydrate “bank” hydrolysis • Breaks the bonds between the glucose monomers • Animals also have enzymes that can hydrolyze plant starch

33. Light ovals in the micrograph are granules of starch within a chloroplast of a plant cell. Simplest form of starch is the amylose. Amylopectin is more complex starch

34. Glycogen • Polymer of glucose similar to polysaccharide but very branched • Humans store this in liver and muscle cells • Hydrolysis releases glucose when the demand for sugar increases • Cannot sustain an animal for long • Stores are depleted in about a day unless they are replenished by consumption of food

36. What is a structural polysaccharide? • Build strong materials from structural polysaccharides • Example: • Cellulose

37. Cellulose microfibrils in a plant cell wall Cell walls Microfibril Cellulose in Plant Cell Walls 0.5 µm Plant cells Cellulose molecules b Glucose monomer

38. Cellulose • Major component of the cell walls in plant cells • Most abundant organic compound on earth • Polymer of glucose • Different glycosidic linkage than those in starch • Glucose monomers are in beta configuration • Every other glucose monomer is upside down • Never branched • Some hydroxyl groups on its glucose monomers are free to hydrogen – bond • In plant cell walls, parallel cellulose molecules held together arranged into microfibrils

39. Cellulose • Enzymes that digest starch by hydrolyzing its alpha linkages cannot hydrolyze the beta linkages of cellulose • Humans cannot digest cellulose • Some animals possess enzymes that can digest cellulose • Some prokaryotes can digest cellulose • In cows and termite guts

40. Chitin • Another structural polysaccharide • Carbohydrate used by arthropods to build exoskeleton • Leathery and flexible • Becomes hardened when encrusted with calcium carbonate • Found in many fungi • Glucose monomer of chitin has a nitrogen-containing appendage

41. Chitin

42. What are Lipids? • Class of large biological molecules • Does not include true polymers • Not big enough to be considered macromolecules • Grouped together because share one important trait • Mix poorly with water • Hydrophobic • Consist mostly of hydrocarbon regions • Vary in form and function

43. Lipids

44. Lipids • Include waxes and certain pigments • Most biologically important types: • Fats • Phospholipds • steroids

45. What are fats? • Not polymers • Large molecules assembled from few smaller molecules • Dehydration reactions • Constructed from 2 kinds of smaller molecules • Glycerol • Fatty acids

46. What are fats? • Major function of fats is energy storage • 1 gram of fat stores more than tice as much energy as a gram of polysaccharide (like starch) • Stored in adipose cells

47. What is a glycerol? • Alcohol with 2 carbon skeleton bearing hydroxyl group

48. What is a fatty acid? • Has a long carbon skeleton • Usually 16 or 18 atoms in length • Carbon at end of fatty acid is part of carboxyl group • What gives it the name fatty acid • Attached to the carboxyl group is a long hydrocarbon chain • Nonpolar C – H bonds in the hydrocarbon chains of fatty acids are the reason fats are hydrophobic

49. Ester Linkage and Lipids Fatty acid (palmitic acid) Glycerol Dehydration reaction in the synthesis of a fat

50. Why do fats separate from water? • Water molecules hydrogen-bond to one another and exclude the fats • Three fatty acid molecules each join to glycerol by an ester linkage when making a fat • Also called a triacylglycerol