Chapter 2: The Molecules of Cells

1. Chapter 2: The Molecules of Cells

2. Basic Chemistry Matter is anything that takes up space and has weight. All matter, living or nonliving, is made up of elements. Elements contain atoms. An atom is the smallest unit of matter that can enter chemical reactions.

3. Atoms have a central nucleus made up of protons and neutrons, and shells around the nucleus in which electrons orbit. inner energy shell holds two electrons outer energy shell holds eight electrons The number of electrons in the outer energy shell determines the chemical properties of the atom.

4. Model of an Atom

5. The atomic number of an atom is its number of protons. protons bear a positive electrical charge The atomic weight of an atom is its number of protons plus its number of neutrons. neutrons bear no electrical charge electrons bear a negative electrical charge An electrically neutral atom means: number of protons = number of electrons

6. Elements are arranged in a periodic table: horizontally in order of increasing atomic number vertically according to the number of electrons in the outer shell

8. Atoms have an atomic symbol, atomic number, and atomic mass. Some atoms differ in their number of neutrons and are called isotopes. Carbon has 3 isotopes: Carbon 12 (most abundant) Carbon 13 Carbon 14 (radioactive - unstable)

9. Atoms form bonds to fill the outer shell with electrons. When atoms bond with other atoms, moleculesare formed. When atoms of different elements bond, a compound is formed. Two types of bonds are ionicbonds and covalent bonds.

10. In ionic bonding, atoms give up or accept electrons, resulting in ions. Ions with opposite charges (- or +) are attracted to each other and form an ionic bond.

11. Ionic Bonds

12. Ions can have important biological functions.

13. Covalent Bonds In covalent reactions, atoms share electrons, resulting in covalent bonds.

14. There are other ways of representing covalent bonds.

15. Aside from single covalent bonds, double, or triple covalent bonds can form.

16. The three-dimensional shape of molecules can be represented in two ways:

17. Water and Living Things • Water is the most abundant molecule in living things. • Water has special traits that make it important to life.

18. Because oxygen atoms are large and hydrogen atoms are small, water is a polar molecule.

19. Hydrogen bonds form when a covalently-bonded H+ is attracted to a negatively-charged atom in a neighboring molecule. Because of its polarity and hydrogen bonding, water has unique characteristics that benefit living things.

20. Characteristics of water: • liquid at room temperature • universal solvent for polar molecules • water molecules are cohesive • temperature of water changes slowly • high heat of vaporization • frozen water is less dense so ice floats

21. Water dissociates and releases hydrogen ions (H+) and hydroxide ions (OH-).

22. Acids are molecules that release hydrogen ions in solution. HCl  H+ + Cl-

23. Bases are molecules that either take up hydrogen ions or give off hydroxide ions in solution. NaOH  Na+ + OH-

24. Concentrations of hydrogen ions or hydroxide ions can be represented using the pH scale. moles/liter 1 x 10 –6 [H+] = pH 6 1 x 10 –7 [H+] = pH 7 1 x 10 –8 [H+] = pH 8

26. Buffersare substances that help to resist change in pH.

27. Organic Molecules Organic molecules are found in living things. The chemistry of carbon accounts for the chemistry of organic molecules. Organic molecules are macromolecules.

29. Hydrocarbon chains can have functional groups that cause the macromolecule to behave in a certain way. (insert text art from top right column of page 31)

30. Macromolecules (polymers) are formed from smaller building blocks called monomers. PolymerMonomer carbohydrate monosaccharides protein amino acid nucleic acid nucleotide

31. Carbohydrates Carbohydrates serve as quick energy and short-term energy storage. They play a structural role in plants, bacteria, and insects. Monomers of carbohydrates are the monosaccharides: glucose fructose galactose

32. Structure of Glucose

33. A disaccharide is made from linking two monosaccharides together.

34. Larger polysaccharides are made from linking many glucose molecules together through condensation synthesis. Examples of polysaccharides: Starch glycogen cellulose

35. Lipids Lipids serve as long-term energy stores in cells, form membranes, and serve as hormones and insulation. Lipids do not dissolve in water. Fats and oils are formed from a glycerol molecule and three fatty acid molecules.

36. Structure of Triglycerides

37. Fatty acids are long chains of hydrocarbons ending in - COOH Fatty acids may be saturated fatty acids or unsaturated fatty acids.

38. Some lipids are phospholipids that form cell membranes.

39. Other lipids are steroids. Examples include cholesterol, and the sex hormones estrogen and testosterone.

40. Proteins Proteins perform many functions in cells. Proteins: Serve as structural proteins Act as enzymes to speed reactions Serve as transport carriers Act as antibodies Allow materials to cross cell membranes

41. Proteins are polymers of amino acids.

42. Peptide bonds join amino acids.

43. Proteins have levels of organization. Proteins can be denatured.

44. Nucleic Acids Nucleic acids are polymers of nucleotides. Examples include Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA).

46. DNA is double-stranded, with complementary base pairing.

47. Some nucleotides also perform functions in cells. Adenosine triphosphate (ATP) is the energy currency of cells.