Chapter 3 Molecules of Life

1. Chapter 3Molecules of Life

2. Carbon – The Stuff of Life • Organicmolecules are complex molecules of life, built on a framework of carbon atoms • Carbohydrates • Lipids • Proteins • Nucleic acids

3. Carbon – The Stuff of Life • Carbon atoms can be assembled and remodeled into many organic compounds • Can bond with one, two, three, or four atoms • Can form polar or nonpolar bonds • Can form chains or rings

4. Take-Home Message:How are all molecules of life alike? • The molecules of life (carbohydrates, lipids, proteins, and nucleic acids) are organic, which means they consist mainly of carbon and hydrogen atoms • The structure of an organic molecule starts with its carbon backbone, a chain of carbon atoms that may form a ring • We use different models to represent different characteristics of a molecule’s structure; considering a molecule’s structural features gives us insight into how it functions

5. 3.3 From Structure to Function • The function of organic molecules in biological systems begins with their structure • The building blocks of carbohydrates, lipids, proteins, and nucleic acids bond together in different arrangements to form different kinds of complex molecules • Any process in which a molecule changes is called a reaction

6. Assembling Complex Molecules • Monomers • Molecules used as subunits to build larger molecules (polymers) • Polymers • Larger molecules that are chains of monomers • May be split and used for energy

7. What Cells Do to Organic Compounds • Metabolism • Activities by which cells acquire and use energy to construct, rearrange, and split organic molecules • Allows cells to live, grow, and reproduce • Requires enzymes (proteins that increase the speed of reactions)

8. What Cells Do to Organic Compounds • Condensation • Covalent bonding of two molecules to form a larger molecule • Water forms as a product • Hydrolysis • The reverse of condensation • Cleavage reactions split larger molecules into smaller ones • Water is split

9. Condensation B Condensation. Cells build a large molecule from smaller ones by this reaction. An enzyme removes a hydroxyl group from one molecule and a hydrogen atom from another. A covalent bond forms between the two molecules, and water also forms.

10. Hydrolysis C Hydrolysis. Cells split a large molecule into smaller ones by this water-requiring reaction. An enzyme attaches a hydroxyl group and a hydrogen atom (both from water) at the cleavage site.

11. Functional Groups • Hydrocarbon • An organic molecule that consists only of hydrogen and carbon atoms • Most biological molecules have at least one functional group • A cluster of atoms that imparts specific chemical properties to a molecule (polarity, acidity)

12. Table 3-1 p41

13. Table 3-1 p41

14. Table 3-1 p41

15. Take-Home Message: How do organic molecules work in living systems? • All life is based on the same organic compounds: complex carbohydrates, lipids, proteins, and nucleic acids • By processes of metabolism, cells assemble these molecules of life form monomers. They also break apart polymers into component monomers. • Functional groups impart chemical characteristics to organic molecules; such groups contribute to the function of biological molecules • An organic molecule’s structure dictates its function in biological systems

16. Carbohydrates • Carbohydrates • Organic molecules that consist of carbon, hydrogen, and oxygen in a 1:2:1 ratio • Three types of carbohydrates in living systems • Monosaccharides (simple sugars) • Oligosaccharides (short-chain carbohydrates) • Polysaccharides (complex carbohydrates)

17. Simple Sugars • Monosaccharides(one sugar unit) are the simplest carbohydrates • Used as an energy source or structural material • Backbones of 5 or 6 carbons • Very soluble in water • Example: glucose

18. Complex Carbohydrates • Polysaccharides • Straight or branched chains of many sugar monomers • The most common polysaccharides are cellulose, starch, and glycogen • All consist of glucose monomers • Each has a different pattern of covalent bonding, and different chemical properties

19. Starch • Starch • Polysaccharide • Energy reservoir in plants • Covalent bonding pattern between monomers makes a chain that coils up into a spiral • Does not dissolve easily in water, but less stable than cellulose • An important component of human food

20. Starch

21. Cellulose • Cellulose • Polysaccharide • Major structural material in plants • Consists of long, straight chains of glucose monomers • Does not dissolve in water; not easily broken down • Dietary fiber or “roughage” in our vegetable foods

22. Cellulose

23. Glycogen • Glycogen • Polysaccharide • Covalent bonding pattern forms highly branched chains of glucose monomers • Energy reservoir in animal cells; stored in muscle and liver cells

24. Glycogen

25. Chitin • Chitin • A nitrogen-containing polysaccharide that strengthens hard parts of animals such as crabs, and cell walls of fungi

26. Take-Home Message: What are carbohydrates? • Simple carbohydrates (sugars), bonded together in different ways, form various types of complex carbohydrates • Cells use carbohydrates for energy or as structural materials

27. 3.5 Greasy, Oily – Must Be Lipids • Lipids function as the body’s major energy reservoir, and as the structural foundation of cell membranes • Lipids • Fatty, oily, or waxy organic compounds that are insoluble in water • Triglycerides, phospholipids, waxes, and steroids are lipids common in biological systems

28. Fatty Acids • Many lipids incorporate fatty acids • Simple organic compounds with a carboxyl group joined to a backbone of 4 to 36 carbon atoms • Saturated fatty acids (animal fats) • Fatty acids with only single covalent bonds • Molecules are packed tightly; solid at room temperature • Unsaturated fatty acids (vegetable oils) • Fatty acids with one or more double bonds • Molecules are kinked; liquid at room temperature

29. Saturated and Unsaturated Fatty Acids

30. Fats • Fats • Lipids with one, two, or three fatty acids “tails” attached to glycerol • Triglycerides • Neutral fats with three fatty acids attached to glycerol • The most abundant energy source in vertebrates • Concentrated in adipose tissues (for insulation and cushioning)

31. Triglycerides

32. Phospholipids • Phospholipids • Molecules with a polar head containing a phosphate and two nonpolar fatty acid tails • Heads are hydrophilic, tails are hydrophobic • The most abundant lipid in cell membranes • Form lipid bilayerswith hydrophobic tails sandwiched between the hydrophilic heads

33. Phospholipids

34. Phospholipids in a Lipid Bilayer one layer of lipids one layer of lipids

35. Waxes • Waxes • Complex mixtures with long fatty-acid tails bonded to long-chain alcohols or carbon rings • Protective, water-repellant covering

36. Steroids • Steroids • Lipids with a rigid backbone of four carbon rings and no fatty-acid tails • Cholesterol • Component of eukaryotic cell membranes • Remodeled into bile salts, vitamin D, and steroid hormones such as the female sex hormone estrogen, and the male sex hormone testosterone

37. Estrogen and Testosterone an estrogen testosterone

38. Effects of Estrogen and Testosterone female wood duck male wood duck

39. Take-Home Message:What are lipids? • Lipids are fatty, waxy, or oily organic compounds. Common types include fats, phospholipids, waxes, and steroids • Triglycerides are lipids that serve as energy reservoirs in vertebrate animals • Phospholipids are the main lipid component of cell membranes • Waxes are lipid components of water-repelling and lubricating secretions • Steroids are lipids that occur in cell membranes; some are remodeled into other molecules

40. 3.6 Proteins – Diversity in Structure and Function • All cellular processes involve proteins, the most diverse biological molecule (structural, nutritious, enzyme, transport, communication, and defense proteins) • Cells build thousands of different proteins by stringing together amino acids in different orders

41. From Structure to Function • Protein • An organic compound composed of one or more chains of amino acids • Amino acid • A small organic compound with an amine group (—NH3+), a carboxyl group (—COO-, the acid), and one or more variable groups (R group)

42. Amino Acid Structure Stepped Art

43. Polypeptides • Protein synthesis involves the formation of amino acid chains called polypeptides • Polypeptide • A chain of amino acids bonded together by peptide bondsin a condensation reaction between the amine group of one amino acid and the carboxyl group of another amino acid

44. methionine serine arginine glutamine serine methionine methionine serine Polypeptide Formation Stepped Art

45. Levels of Protein Structure • Primary structure • The unique amino acid sequence of a protein • Secondary structure • The polypeptide chain folds and forms hydrogen bonds between amino acids • Tertiary structure • A secondary structure is compacted into structurally stable units called domains • Forms a functional protein

46. Levels of Protein Structure • Quaternary structure • Some proteins consist of two or more folded polypeptide chains in close association • Example: hemoglobin • Some proteins aggregate by thousands into larger structures, with polypeptide chains organized into strands or sheets • Example: hair

47. arginine lysine glycine glycine Tertiary structure occurs when a chain’s coils and sheets fold up into a functional domain such as a barrel or pocket. In this example, the coils of a globin chain form a pocket. 3 Many proteins aggregate by the thousands into much larger structures, such as the keratin filaments that make up hair. 5 A protein’s primary structure consists of a linear sequence of amino acids (a polypeptide chain). Each type of protein has a unique primary structure. Secondary structure arises as a polypeptide chain twists into a coil (helix) or sheet held in place by hydrogen bonds between different parts of the molecule. The same patterns of secondary structure occur in many different proteins. 2 1 Some proteins have quaternary structure, in which two or more polypeptide chains associate as one molecule. Hemoglobin, shown here, consists of four globin chains (green and blue). Each globin pocket now holds a heme group (red). 4 Stepped Art Figure 3-16 p47

48. Take-Home Message:What are proteins? • Proteins are chains of amino acids. The order of amino acids in a polypeptide chain dictates the type of protein. • Polypeptide chains twist and fold into coils, sheets, and loops, which fold and pack further into functional domains • A protein’s shape is the source of its function

49. 3.7 Why Is Protein Structure So Important? • Proteins function only as long as they maintain their correct three-dimensional shape • Changes in a protein’s shape may have drastic health consequences

50. Denaturation • Heat, changes in pH, salts, and detergents can disrupt the hydrogen bonds that maintain a protein’s shape • When a protein loses its shape and no longer functions, it is denatured • Once a protein’s shape unravels, so does its function