Proteins, Carbohydrates, and Lipids

1. Proteins, Carbohydrates,and Lipids

2. 3 Proteins, Carbohydrates, and Lipids • 3.1 What Kinds of Molecules Characterize Living Things? • 3.2 What Are the Chemical Structures and Functions of Proteins? • 3.3 What Are the Chemical Structures and Functions of Carbohydrates? • 3.4 What Are the Chemical Structures and Functions of Lipids?

3. 3 Proteins, Carbohydrates, and Lipids • Spider silk is composed of proteins. The protein molecules in different types of silk have different structural characteristics and functions. Opening Question: Can knowledge of spider web protein structure be put to practical use?

4. 3.1 What Kinds of Molecules Characterize Living Things? • Molecules that make up living organisms: • Proteins • Carbohydrates • Lipids • Nucleic acids • Most are polymers of smaller molecules called monomers.

5. 3.1 What Kinds of Molecules Characterize Living Things? • Proteins: combinations of 20 amino acids. • Carbohydrates: sugar monomers (monosaccharides) are linked to form polysaccharides. • Nucleic acids: four kinds of nucleotide monomers. • Lipids: noncovalent forces maintain interactions between lipid monomers.

6. 3.1 What Kinds of Molecules Characterize Living Things? • Macromolecules: polymers with molecular weights >1,000. • Macromolecule function depends on the properties of functional groups— groups of atoms with specific chemical properties and consistent behavior. • A single macromolecule may contain many different functional groups.

7. Figure 3.1 Some Functional Groups Important to Living Systems (Part 1)

8. Figure 3.1 Some Functional Groups Important to Living Systems (Part 2)

9. Figure 3.1 Some Functional Groups Important to Living Systems (Part 3)

10. 3.1 What Kinds of Molecules Characterize Living Things? • Isomers: molecules with the same chemical formula, but atoms are arranged differently. • Structural isomers • cis-trans isomers • Optical isomers

11. 3.1 What Kinds of Molecules Characterize Living Things? • Structural isomers: differ in how their atoms are joined together.

12. 3.1 What Kinds of Molecules Characterize Living Things? • cis-trans isomers: different orientation around a double bond.

13. 3.1 What Kinds of Molecules Characterize Living Things? • Optical isomers occur when a carbon atom has four different atoms or groups attached to it (an asymmetric carbon). • Some biochemical molecules that can interact with one optical isomer are unable to “fit” the other isomer.

14. Figure 3.2 Isomers (Part 2)

15. 3.1 What Kinds of Molecules Characterize Living Things? • Biochemical unity:the four kinds of macromolecules are present in the same proportions in all living organisms and have similar functions. • Organisms can obtain required macromolecules by eating other organisms.

16. Figure 3.3 Substances Found in Living Tissues

17. 3.1 What Kinds of Molecules Characterize Living Things? • Macromolecule functions are directly related to their three-dimensional shapes and the sequence and chemical properties of the monomers.

18. 3.1 What Kinds of Molecules Characterize Living Things? • Polymers are formed in condensation reactions. • Monomers are joined by covalent bonds; energy must be added. • A water is removed; they are also called dehydrationreactions.

19. 3.1 What Kinds of Molecules Characterize Living Things? • Polymers are broken down into monomers in hydrolysis reactions (hydro, “water”; lysis, “break”). • Hydrolysis releases energy.

20. Figure 3.4 Condensation and Hydrolysis of Polymers

21. 3.2 What Are the Chemical Structures and Functions of Proteins? • Proteins have diverse functions. Only energy storage and information storage are not performed by proteins.

22. Table 3.1

23. 3.2 What Are the Chemical Structures and Functions of Proteins? • Proteins are polymers of 20 different amino acids. • Polypeptide chain: single, unbranched chain of amino acids. • Proteins consist of one or more polypeptide chains, which are folded into specific 3-D shapes defined by the sequence of amino acids.

24. 3.2 What Are the Chemical Structures and Functions of Proteins? • Amino acids have carboxyl and amino groups—they function as both acid and base. • IN-TEXT art, p. 5

25. 3.2 What Are the Chemical Structures and Functions of Proteins? • The α carbon atom is asymmetrical. • Amino acids exist in two isomeric forms: • D-amino acids (dextro, right) • L-amino acids (levo, left)—this form is found in organisms

26. 3.2 What Are the Chemical Structures and Functions of Proteins? • The side chains or R-groups also have functional groups. • Amino acids can be grouped based on the side chains.

27. 3.2 What Are the Chemical Structures and Functions of Proteins? • These hydrophilic amino acids attract ions of opposite charges.

28. Table 3.2 (Part 2)

29. 3.2 What Are the Chemical Structures and Functions of Proteins? Hydrophilic amino acids with polar but uncharged side chains form hydrogen bonds.

30. 3.2 What Are the Chemical Structures and Functions of Proteins? • Hydrophobic amino acids

31. Table 3.2 The Twenty Amino Acids (Part C)

32. 3.2 What Are the Chemical Structures and Functions of Proteins? • The terminal —SH group of cysteine can react with another cysteine side chain to form a disulfide bridge, or disulfide bond (—S—S—). • These are important in protein folding.

33. Figure 3.5 A Disulfide Bridge

34. 3.2 What Are the Chemical Structures and Functions of Proteins? • Glycine is small and fits into tight corners in the interior of proteins. • The proline side chain forms a ring, which limits its hydrogen-bonding ability and its ability to rotate about the α carbon. It is often found where a protein bends or loops.

35. 3.2 What Are the Chemical Structures and Functions of Proteins? • Amino acids bond together covalently in a condensation reaction by peptide linkages (peptide bonds).

36. Figure 3.6 Formation of Peptide Linkages

37. 3.2 What Are the Chemical Structures and Functions of Proteins? • A polypeptide chain is like a sentence: • • The “capital letter” is the amino group of the first amino acid—the N terminus. • • The “period” is the carboxyl group of the last amino acid—the C terminus.

38. 3.2 What Are the Chemical Structures and Functions of Proteins? • The primary structure of a protein is the sequence of amino acids. • The sequence determines secondary and tertiary structure—how the protein is folded. • The number of different proteins that can be made from 20 amino acids is enormous!

39. Figure 3.7 The Four Levels of Protein Structure (Part 1)

40. 3.2 What Are the Chemical Structures and Functions of Proteins? • Secondary structure: • •α helix—right-handed coil resulting from hydrogen bonding between N–H groups on one amino acid and C=O groups on another. • •β pleated sheet—two or more polypeptide chains are aligned; hydrogen bonds form between the chains.

41. Figure 3.7 The Four Levels of Protein Structure (Part 2)

42. Figure 3.8 Left- and Right-Handed Helices

43. 3.2 What Are the Chemical Structures and Functions of Proteins? • Tertiary structure: Bending and folding results in a macromolecule with specific three-dimensional shape. • The outer surfaces present functional groups that can interact with other molecules.

44. Figure 3.7 The Four Levels of Protein Structure (D)

45. 3.2 What Are the Chemical Structures and Functions of Proteins? • Tertiary structure is determined by interactions between R-groups: • Disulfide bridges • Hydrogen bonds • Aggregation of hydrophobic side chains • Ionic attractions

46. 3.2 What Are the Chemical Structures and Functions of Proteins? • Ionic attractions form salt bridges between positively and negatively charged amino acids.

47. Figure 3.9 Three Representations of Lysozyme

48. Figure 3.9 Three Representations of Lysozyme • Complete descriptions of tertiary structure have been worked out for many proteins.

49. 3.2 What Are the Chemical Structures and Functions of Proteins? • If a protein is heated, secondary and tertiary structure break down; the protein is said to be denatured. • When cooled, the protein returns to normal tertiary structure, demonstrating that the information to specify protein shape is in the primary structure.

50. Figure 3.10 Primary Structure Specifies Tertiary Structure (Part 1)