Molecules of Life

1. Molecules of Life Chapter 3 Part 2

2. 3.5 Proteins – Diversity in Structure and Function • Proteins are 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

3. Proteins and Amino Acids • 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)

4. Amino Acid Structure

5. amine group carboxyl group valine Fig. 3-15, p. 44

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

7. Peptide Bond Formation

8. Fig. 3-16a, p. 44

9. A DNA encodes the order of amino acids in a new polypeptide chain. Methionine (met) is typically the first amino acid. B In a condensation reaction, a peptide bond forms between the methionine and the next amino acid, alanine (ala) in this example. Leucine (leu) will be next. Think about polarity, charge, and other properties of functional groups that become neighbors in the growing chain. Fig. 3-16a, p. 44

10. Fig. 3-16b, p. 45

11. C A peptide bond forms between the alanine and leucine. Tryptophan (trp) will be next. The chain is starting to twist and fold as atoms swivel around some bonds and attract or repel their neighbors. D The sequence of amino acid subunits in this newly forming peptide chain is now met–ala–leu–trp. The process may continue until there are hundreds or thousands of amino acids in the chain. Fig. 3-16b, p. 45

12. A DNA encodes the order of amino acids in a new polypeptide chain. Methionine (met) is typically the first amino acid. B In a condensation reaction, a peptide bond forms between the methionine and the next amino acid, alanine (ala) in this example. Leucine (leu) will be next. Think about polarity, charge, and other properties of functional groups that become neighbors in the growing chain. Stepped Art Fig. 3-16a, p. 44

13. C A peptide bond forms between the alanine and leucine. D The sequence of amino acid subunits in this newly forming peptide chain is now met–ala–leu–trp. The process may continue until there are hundreds or thousands of amino acids in the chain. Tryptophan (trp) will be next. The chain is starting to twist and fold as atoms swivel around some bonds and attract or repel their neighbors. Stepped Art Fig. 3-16b, p. 45

14. Animation: Peptide bond formation

15. 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

16. Levels of Protein Structure • Tertiary structure • A secondary structure is compacted into structurally stable units called domains • Forms a functional protein • Quaternary structure • Some proteins consist of two or more folded polypeptide chains in close association • Example: hemoglobin

17. Levels of Protein Structure

18. 3.6 Why Is Protein Structure So Important? • When a protein’s structure goes awry, so does its function

19. Fig. 3-17a, p. 45

20. a Protein primary structure: Amino acids bonded as a polypeptide chain. Fig. 3-17a, p. 45

21. Fig. 3-17b, p. 45

22. b Protein secondary structure: A coiled (helical) or sheetlike array held in place by hydrogen bonds (dotted lines) between different parts of the polypeptide chain. helix (coil) sheet Fig. 3-17b, p. 45

23. Fig. 3-17c, p. 45

24. c Protein tertiary structure: A chain’s coils, sheets, or both fold and twist into stable, functional domains such as barrels or pockets. barrel Fig. 3-17c, p. 45

25. Fig. 3-17d, p. 45

26. d Protein quaternary structure: two or more polypeptide chains associated as one molecule. Fig. 3-17d, p. 45

27. a) Protein primary structure: Amino acids bonded as a polypeptide chain. b) Protein secondary structure: A coiled (helical) or sheetlike array held in place by hydrogen bonds (dotted lines) between different parts of the polypeptide chain. helix (coil) sheet c) Protein tertiary structure: A chain’s coils, sheets, or both fold and twist into stable, functional domains such as barrels or pockets. barrel d) Protein quaternary structure: two or more polypeptide chains associated as one molecule. Stepped Art Fig. 3-17, p. 45

28. Just One Wrong Amino Acid… • Hemoglobin contains four globin chains, each with an iron-containing heme group that binds oxygen and carries it to body cells • In sickle cell anemia, a DNA mutation changes a single amino acid in a beta chain, which changes the shape of the hemoglobin molecule, causing it to clump and deform red blood cells

29. Globin Chains in Hemoglobin

30. Fig. 3-18a, p. 46

31. alpha globin heme A Globin. The secondary structure of this protein includes several helices. The coils fold up to form a pocket that cradles heme, a functional group with an iron atom at its center. Fig. 3-18a, p. 46

32. Fig. 3-18b, p. 46

33. alpha globin alpha globin beta globin beta globin B Hemoglobin is one of the proteins with quaternary structure. It consists of four globin molecules held together by hydrogen bonds. To help you distinguish among them, the two alpha globin chains are shown here in green, and the two beta globin chains are in brown. Fig. 3-18b, p. 46

34. Animation: Globin and hemoglobin structure

35. Molecular Basis of Sickle Cell Anemia

36. Fig. 3-19a, p. 47

37. glutamic acid glutamic acid valine histidine leucine threonine proline A Normal amino acid sequence at the start of the hemoglobin beta chain. Fig. 3-19a, p. 47

38. Fig. 3-19b, p. 47

39. valine histidine leucine threonine proline valine glutamic acid B One amino acid substitution results in the abnormal beta chain of HbS molecules. The sixth amino acid in such chains is valine, not glutamic acid. Fig. 3-19b, p. 47

40. Fig. 3-19c, p. 47

41. C Glutamic acid carries a negative charge; valine carries no charge. This difference changes the protein so it behaves differently. At low oxygen levels, HbS molecules stick together and form rod-shaped clumps that distort normally rounded red blood cells into sickle shapes. (A sickle is a farm tool that has a crescent-shaped blade.) sickled cell normal cell Fig. 3-19c, p. 47

42. Fig. 3-19d, p. 47

43. Clumping of cells in bloodstream Circulatory problems, damage to brain, lungs, heart, skeletal muscles, gut, and kidneys Heart failure, paralysis, pneumonia, rheumatism, gut pain, kidney failure Spleen concentrates sickle cells Spleen enlargement Immune system compromised Rapid destruction of sickle cells Anemia, causing weakness, fatigue, impaired development, heart chamber dilation Impaired brain function, heart failure D Melba Moore is a celebrity spokesperson for sickle-cell anemia organizations. Right, range of symptoms for a person with two mutated genes for hemoglobin’s beta chain. Fig. 3-19d, p. 47

44. Animation: Sickle-cell anemia

45. Proteins Undone – Denaturation • Proteins function only as long as they maintain their correct three-dimensional shape • 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

46. 3.5-3.6 Key Concepts:Proteins • Structurally and functionally, proteins are the most diverse molecules of life • They include enzymes, structural materials, and transporters • A protein’s function arises directly from its structure

47. 3.7 Nucleic Acids • Some nucleotides are subunits of nucleic acids such as DNA and RNA • Some nucleotides have roles in metabolism

48. Nucleotides • Nucleotide • A small organic molecule consisting of a sugar with a five-carbon ring, a nitrogen-containing base, and one or more phosphate groups • ATP • A nucleotide with three phosphate groups • Important in phosphate-group (energy) transfer

49. ATP

50. base (adenine) sugar (ribose) 3 phosphate groups Fig. 3-20, p. 48