Biological Molecules

1. 3 Biological Molecules 0

2. Chapter 3 At a Glance • 3.1 Why Is Carbon So Important in Biological Molecules? • 3.2 How Are Organic Molecules Synthesized? • 3.3 What Are Carbohydrates? • 3.4 What Are Lipids? • 3.5 What Are Proteins? • 3.6 What Are Nucleotides and Nucleic Acids?

3. 3.1 Why Is Carbon So Important in Biological Molecules? • Organic refers to molecules containing a carbon skeleton bonded to hydrogen atoms • Inorganic refers to carbon dioxide and all molecules without carbon

4. 3.1 Why Is Carbon So Important in Biological Molecules? • The unique bonding properties of carbon are key to the complexity of organic molecules • The carbon atom is versatile because it has four electrons in an outermost shell that can accommodate eight electrons • Therefore, a carbon atom can become stable by forming up to four bonds (single, double, or triple) • As a result, organic molecules can assume complex shapes, including branched chains, rings, sheets, and helices

5. Figure 3-1 Bonding patterns H hydrogen C C C C carbon N N N nitrogen O O oxygen

6. 3.1 Why Is Carbon So Important in Biological Molecules? • The unique bonding properties of carbon are key to the complexity of organic molecules (continued) • Functional groups in organic molecules determine the characteristics and chemical reactivity of the molecules • Functional groups are less stable than the carbon backbone and are more likely to participate in chemical reactions

7. Table 3-1

8. 3.2 How Are Organic Molecules Synthesized? • Small organic molecules (called monomers) are joined to form longer molecules (called polymers) • Biomolecules are joined or broken through dehydration synthesis or hydrolysis

9. 3.2 How Are Organic Molecules Synthesized? • Biological polymers are formed by removing water and split apart by adding water • Monomers are joined together through dehydration synthesis, at the site where an H and an OH are removed, resulting in the loss of a water molecule (H2O) • The openings in the outer electron shells of the two subunits are filled when the two subunits share electrons, creating a covalent bond

10. Figure 3-2 Dehydration synthesis dehydration synthesis

11. 3.2 How Are Organic Molecules Synthesized? • Biological polymers are formed by removing water and split apart by adding water (continued) • Polymers are broken apart through hydrolysis (“water cutting”) • Water is broken into H and OH and is used to break the bond between monomers

12. Animation: Dehydration Synthesis and Hydrolysis

13. Figure 3-3 Hydrolysis hydrolysis

14. 3.2 How Are Organic Molecules Synthesized? • Biological polymers are formed by removing water and split apart by adding water (continued) • All biological molecules fall into one of four categories • Carbohydrates • Lipids • Proteins • Nucleotides/nucleic acids

15. Table 3-2

16. 3.3 What Are Carbohydrates? • Carbohydrate molecules are composed of C, H, and O in the ratio of 1:2:1 • If a carbohydrate consists of just one sugar molecule, it is a monosaccharide • Two linked monosaccharides form a disaccharide • A polymer of many monosaccharides is a polysaccharide • Carbohydrates are important energy sources for most organisms • Most small carbohydrates are water-soluble due to the polar OH functional group

17. 3.3 What Are Carbohydrates? • There are several monosaccharides with slightly different structures • The basic monosaccharide structure is a backbone of 3–7 carbon atoms • Most of the carbon atoms have both a hydrogen (-H) and a hydroxyl group (-OH) attached to them • Most carbohydrates have the approximate chemical formula (CH2O)n where “n” is the number of carbons in the backbone • When dissolved in the cytoplasmic fluid of a cell, the carbon backbone usually forms a ring

18. 3.3 What Are Carbohydrates? • There are several monosaccharides with slightly different structures (continued) • Glucose (C6H12O6) is the most common monosaccharide in living organisms

19. Figure 3-4 Sugar dissolving in water water hydrogen bond hydroxyl group

20. Figure 3-5 Depictions of glucose structure 5 3 1 6 4 2 Linear, ball and stick Chemical formula 6 6 5 5 1 4 1 4 3 2 3 2 Ring, simplified Ring, ball and stick

21. 3.3 What Are Carbohydrates? • There are several monosaccharides with slightly different structures (continued) • Additional monosaccharides are • Fructose (“fruit sugar” found in fruits, corn syrup, and honey) • Galactose (“milk sugar” found in lactose) • Ribose and deoxyribose (found in RNA and DNA, respectively)

22. Figure 3-6 Some six-carbon monosaccharides 6 6 5 4 1 2 5 4 3 3 1 2 galactose fructose

23. Figure 3-7 Some five-carbon monosaccharides 5 5 4 4 1 1 2 2 3 3 Note “missing” oxygen atom deoxyribose ribose

24. 3.3 What Are Carbohydrates? • Disaccharides consist of two monosaccharides linked by dehydration synthesis • The fate of monosaccharides inside a cell can be • Some are broken down to free their chemical energy • Some are linked together by dehydration synthesis

25. 3.3 What Are Carbohydrates? • Disaccharides consist of two monosaccharides linked by dehydration synthesis (continued) • Disaccharides are two-part sugars • They are used for short-term energy storage • When energy is required, they are broken apart into their monosaccharide subunits by hydrolysis

26. Figure 3-8 Synthesis of a disaccharide sucrose glucose fructose dehydration synthesis

27. 3.3 What Are Carbohydrates? • Disaccharides consist of two monosaccharides linked by dehydration synthesis (continued) • Examples of disaccharides include • Sucrose (table sugar)  glucose  fructose • Lactose (milk sugar)  glucose  galactose • Maltose (malt sugar)  glucose  glucose

28. 3.3 What Are Carbohydrates? • Polysaccharides are chains of monosaccharides • Storage polysaccharides include • Starch, an energy-storage molecule in plants, formed in roots and seeds • Glycogen, an energy-storage molecule in animals, found in the liver and muscles • Both starch and glycogen are polymers of glucose molecules

29. Figure 3-9 Starch structure and function starch grains Potato cells Detail of a starch molecule A starch molecule

30. 3.3 What Are Carbohydrates? • Polysaccharides are chains of monosaccharides (continued) • Many organisms use polysaccharides as a structural material • Cellulose (a polymer of glucose) is one of the most important structural polysaccharides • It is found in the cell walls of plants • It is indigestible for most animals due to the orientation of the bonds between glucose molecules

31. Animation: Carbohydrate Structure and Function

32. Figure 3-10 Cellulose structure and function A plant cell with a cell wall Cellulose is a major component of wood A close-up of cellulose fibers in a cell wall Hydrogen bonds cross-linking cellulose molecules bundle of cellulose molecules cellulose fiber Alternating bond configuration differs from starch Detail of a cellulose molecule

33. 3.3 What Are Carbohydrates? • Polysaccharides are chains of monosaccharides (continued) • Chitin (a polymer of modified glucose units) is found in • The outer coverings of insects, crabs, and spiders • The cell walls of many fungi

34. Figure 3-11 Chitin structure and function

35. 3.4 What Are Lipids? • Lipids are a diverse group of molecules that contain regions composed almost entirely of hydrogen and carbon • All lipids contain large chains of nonpolar hydrocarbons • Most lipids are therefore hydrophobic and water insoluble

36. Animation: Lipids

37. 3.4 What Are Lipids? • Lipids are diverse in structure and serve a variety of functions • They are used for energy storage • They form waterproof coverings on plant and animal bodies • They serve as the primary component of cellular membranes • Still others are hormones

38. 3.4 What Are Lipids? • Lipids are classified into three major groups • Oils, fats, and waxes • Phospholipids • Steroids containing rings of carbon, hydrogen, and oxygen

39. 3.4 What Are Lipids? • Oils, fats, and waxes are lipids containing only carbon, hydrogen, and oxygen • Oils, fats, and waxes are made of one or more fatty acid subunits

40. 3.4 What Are Lipids? • Oils, fats, and waxes are lipids containing only carbon, hydrogen, and oxygen (continued) • Fats and oils • Are used primarily as energy-storage molecules, containing twice as many calories per gram as carbohydrates and proteins • Are formed by dehydration synthesis • Three fatty acids glycerol triglyceride

41. Figure 3-12 Synthesis of a triglyceride fatty acids glycerol triglyceride

42. Figure 3-13a Fat Fat

43. 3.4 What Are Lipids? • Oils, fats, and waxes are lipids containing only carbon, hydrogen, and oxygen (continued) • Fats that are solid at room temperature are saturated (the carbon chain has as many hydrogen atoms as possible, and mostly or all C–C bonds); for example, beef fat

44. Figure 3-14a A fat A fat

45. 3.4 What Are Lipids? • Oils, fats, and waxes are lipids containing only carbon, hydrogen, and oxygen (continued) • Fats that are liquid at room temperature are unsaturated (with fewer hydrogen atoms, and many CC bonds); for example, corn oil • Unsaturated trans fats have been linked to heart disease

46. Figure 3-14b An oil An oil

47. 3.4 What Are Lipids? • Oils, fats, and waxes are lipids containing only carbon, hydrogen, and oxygen (continued) • Waxes are highly saturated and solid at room temperature • Waxes form waterproof coatings such as on • Leaves and stems in plants • Fur in mammals • Insect exoskeletons • Waxes are also used to build honeycomb structures

48. Figure 3-13b Wax Wax

49. 3.4 What Are Lipids? • Phospholipids have water-soluble “heads” and water-insoluble “tails” • These form plasma membranes around all cells • Phospholipids consist of two fatty acids  glycerol  a short polar functional group • They have hydrophobic and hydrophilic portions • The polar functional groups form the “head” and are water soluble • The nonpolar fatty acids form the “tails” and are water insoluble

50. Figure 3-15 Phospholipids variable functional group phosphate group glycerol backbone polar head fatty acid tails (hydrophobic) (hydrophilic)