The Chemistry and Energy of Life

1. 2 The Chemistry and Energyof Life

2. Chapter 2 The Chemistry and Energy of Life • Key Concepts • 2.1 Atomic Structure Is the Basis for Life’s Chemistry • 2.2 Atoms Interact and Form Molecules • 2.3 Carbohydrates Consist of Sugar Molecules • 2.4 Lipids Are Hydrophobic Molecules • 2.5 Biochemical Changes Involve Energy

3. Chapter 2 Opening Question • Why is the search for water important in the search for life?

4. Concept 2.1 Atomic Structure Is the Basis for Life’s Chemistry • Living and nonliving matter is composed of atoms.

5. Concept 2.1 Atomic Structure Is the Basis for Life’s Chemistry • Like charges repel; different charges attract. • Most atoms are neutral because the number of electrons equals the number of protons.

6. Concept 2.1 Atomic Structure Is the Basis for Life’s Chemistry • Dalton—mass of one proton or neutron • (1.7 × 10–24 grams) • Mass of electrons is so tiny, it is usually ignored.

7. Concept 2.1 Atomic Structure Is the Basis for Life’s Chemistry • Element—pure substance that contains only one kind of atom • Living things are mostly composed of six elements: • Carbon (C) Hydrogen (H) Nitrogen (N) • Oxygen (O) Phosphorus (P) Sulfur (S)

8. Concept 2.1 Atomic Structure Is the Basis for Life’s Chemistry • The number of protons identifies an element. • Number of protons = atomic number • For electrical neutrality: protons = electrons • Mass number is the number of protons plus neutrons

9. Concept 2.1 Atomic Structure Is the Basis for Life’s Chemistry • Bohr model for atomic structure: atom is largely empty space; the electrons occur in orbits, or electron shells.

10. Concept 2.1 Atomic Structure Is the Basis for Life’s Chemistry • Bohr models are simplified, but useful in understanding how atoms behave. • Behavior of electrons determines whether a chemical bond will form between atoms and what shape the bond will have.

11. Figure 2.1 Electron Shells

12. Concept 2.1 Atomic Structure Is the Basis for Life’s Chemistry • Octet rule: for elements 6–20, an atom will lose, gain, or share electrons in order to achieve a stable configuration of 8 electrons in its outermost shell. • When atoms share electrons, they form stable associations called molecules.

13. Concept 2.2 Atoms Interact and Form Molecules • A chemical bond is an attractive force that links atoms together in molecules. • There are several kinds of chemical bonds.

14. Table 2.1

15. Concept 2.2 Atoms Interact and Form Molecules • Covalent bonds form when two atoms share pairs of electrons. • The atoms attain stability by having full outer shells. • Each atom contributes one member of the electron pair.

16. Figure 2.2 Electrons Are Shared in Covalent Bonds

17. Concept 2.2 Atoms Interact and Form Molecules • Carbon atoms have 6 electrons; 4 in the outer shell. • They can form covalent bonds with four other atoms.

18. Figure 2.3 Covalent Bonding

19. Table 2.2

20. Concept 2.2 Atoms Interact and Form Molecules • Properties of molecules are influenced by characteristics of the covalent bonds: • Orientation—length, angle, and direction of bonds between any two elements are always the same.Example: Methane always forms a tetrahedron.

21. Concept 2.2 Atoms Interact and Form Molecules • N N • C H • C C • Strength and stability—covalent bonds are very strong; it takes a lot of energy to break them. • Multiple bonds Single—sharing 1 pair of electrons Double—sharing 2 pairs of electrons Triple—sharing 3 pairs of electrons

22. Concept 2.2 Atoms Interact and Form Molecules • Two atoms of different elements do not always share electrons equally. • The nucleus of one element may have greater electronegativity—the attractive force that an atomic nucleus exerts on electrons. • Depends on the number of protons and the distance between the nucleus and electrons.

23. Table 2.3

24. Concept 2.2 Atoms Interact and Form Molecules • If atoms have similar electronegativities, they share electrons equally (nonpolar covalent bond). • If atoms have different electronegativities, electrons tend to be near the most attractive atom, forming a polar covalent bond.

25. Concept 2.2 Atoms Interact and Form Molecules • The partial charges that result from polar covalent bonds produce polar molecules or polar regions of large molecules. • Polar bonds influence interactions with other molecules. • Polarity of water molecules determines many of water’s unique properties.

26. Concept 2.2 Atoms Interact and Form Molecules • Hydrogen bonds: • Attraction between the δ– end of one molecule and the δ+ hydrogen end of another molecule. • They form between water molecules and within larger molecules. • Although much weaker than covalent bonds, they are important in the structure of DNA and proteins.

27. Figure 2.4 Hydrogen Bonds Can Form between or within Molecules

28. Concept 2.2 Atoms Interact and Form Molecules • Hydrogen bonding contributes to properties of water that are significant for life: • Water is a solvent in living systems—a liquid in which other molecules dissolve. • Water molecules form multiple hydrogen bonds with each other—this contributes to high heat capacity.

29. In-Text Art, Chapter 2, p. 23

30. Concept 2.2 Atoms Interact and Form Molecules • A lot of heat energy is required to raise the temperature of water—the heat energy breaks the hydrogen bonds. • In organisms, presence of water shields them from fluctuations in environmental temperature.

31. Concept 2.2 Atoms Interact and Form Molecules • Water has a high heat of vaporization: a lot of heat energy is required to change water from the liquid to gaseous state (to break the hydrogen bonds). • Thus, evaporation has a cooling effect on the environment. • Sweating cools the body—as sweat evaporates from the skin, it absorbs some of the adjacent body heat.

32. Concept 2.2 Atoms Interact and Form Molecules • Hydrogen bonds give water cohesive strength, or cohesion—water molecules resist coming apart when placed under tension. • Hydrogen bonding between liquid water molecules and solid surfaces allows for adhesion between the water and the solid surface.

33. In-Text Art, Chapter 2, p. 24

34. Concept 2.2 Atoms Interact and Form Molecules • Cohesion and adhesion allow narrow columns of water to move from roots to the leaves of plants. • Surface tension: water molecules at the surface are hydrogen-bonded to other molecules below them, making the surface difficult to puncture. This allows spiders to walk on the surface of a pond.

35. Concept 2.2 Atoms Interact and Form Molecules • Any polar molecule can interact with any other polar molecule through hydrogen bonds. • Hydrophilic (“water-loving”): in aqueous solutions, polar molecules become separated and surrounded by water molecules. • Nonpolar molecules are called hydrophobic (“water-hating”); the interactions between them are hydrophobic interactions.

36. Figure 2.5 Hydrophilic and Hydrophobic

37. Concept 2.2 Atoms Interact and Form Molecules • When one atom is much more electronegative than the other, a complete transfer of electrons may occur. • This makes both atoms more stable because their outer shells are full. • The result is two ions—electrically charged particles that form when atoms gain or lose one or more electrons.

38. Figure 2.6 Ionic Attraction between Sodium and Chlorine

39. Concept 2.2 Atoms Interact and Form Molecules • Cations—positively charged ions • Anions—negatively charged ions • Ionic attractions result from the electrical attraction between ions with opposite charges. The resulting molecules are called salts or ionic compounds.

40. Concept 2.2 Atoms Interact and Form Molecules • Ionic attractions are weak, so salts dissolve easily in water. • place text art pg 25 here

41. Concept 2.2 Atoms Interact and Form Molecules • Functional groups—small groups of atoms with specific chemical properties • Functional groups confer these properties to larger molecules (e.g., polarity). • One biological molecule may contain many functional groups that determine molecular shape and reactivity.

42. Figure 2.7 Functional Groups Important to Living Systems (Part 1)

43. Figure 2.7 Functional Groups Important to Living Systems (Part 2)

44. Figure 2.7 Functional Groups Important to Living Systems (Part 3)

45. In-Text Art, Chapter 2, p. 26

46. Concept 2.2 Atoms Interact and Form Molecules • Proteins—formed from different combinations of 20 amino acids • Carbohydrates—formed by linking sugar monomers (monosaccharides) to form polysaccharides • Nucleic acids—formed from four kinds of nucleotidemonomers • Lipids—noncovalent forces maintain the interactions between the lipid monomers

47. Concept 2.2 Atoms Interact and Form Molecules • Polymers are formed and broken apart in reactions involving water. • Condensation—removal of water links monomers together • Hydrolysis—addition of water breaks a polymer into monomers

48. Figure 2.8 Condensation and Hydrolysis of Polymers (Part 1)

49. Figure 2.8 Condensation and Hydrolysis of Polymers (Part 2)

50. Concept 2.3 Carbohydrates Consist of Sugar Molecules • Carbohydrates • Source of stored energy • Transport stored energy within organisms • Structural molecules give many organisms their shapes • Recognition or signaling molecules can trigger specific biological responses