Chapter 2: Cell Chemistry and Biosynthesis

1. Chapter 2:Cell Chemistry and Biosynthesis

2. Organisms are composed of matterMatter is anything that takes up space and has mass

3. Cells Are Made From a Few Types of Atoms Element – substance that cannot be broken down to other substances by chemical reactions Atom – smallest particle of an element Molecules – groups of atoms Atomic weight– mass of atom relative to that of hydrogen atom (protons + neutrons) Molecular weight – sum of the atomic weights of all of the atoms in compound Figure 2-1

4. Subatomic Particles • Atoms are composed of subatomic particles • Relevant subatomic particles include: • Neutrons (no electrical charge) • Protons (positive charge) • Electrons (negative charge)

5. Cloud of negative charge (2 electrons) Electrons Nucleus • Neutrons and protons form the atomic nucleus • Electrons form a cloud around the nucleus • Neutron mass and proton mass are almost identical and are measured in daltons (b) (a)

6. Isotopes • All atoms of an element have the same number of protons but may differ in number of neutrons • Isotopesare two atoms of an element that differ in number of neutrons

7. 1 gram of hydrogen – • 6 x 1023 atoms • Avogadro number • 89 naturally found elements: • differ in number of protons and electrons in their atoms • - C, H, N, O – 96.5% of the living organisms weight Figure 2-2

8. Chemical elements in the • nonliving world • differs significantly from • the composition of the • Living word Figure 2-3

9. The Outermost Electrons Determine Atom Interactions • Living organisms: • - only electrons have rearrangements • Electrons: • continuous movement around the nucleus; • exist in certain states (orbitals); • Electron shell: • -orbital of certain type with set number of electrons in it; • -innermost shell holds maximum of 2 electrons; • -the second shell has max of 8 electrons; • the third shell – max 8 • 4th and 5th shells – max 18 Figure 2-4

10. Electrons mostly fill the orbitals in order: • - most stable in the innermost shells;- If outermost shell is filled :atom is very stable and chemically unreactive; • Unfilled outermost shells: • atoms less sable and chemically reactive; • interact with other atoms by gaining or losing electrons to fill the outermost • shell • Electrons mostly fill the orbitals in order: • - most stable in the innermost shells;- If outermost shell is filled :atom is very stable and chemically unreactive; • Unfilled outermost shells: • atoms less sable and chemically reactive; • interact with other atoms by gaining or losing electrons to fill the outermost • shell red – unfilled outermost shells yellow – filled shells (unreactive) Figure 2-4

11. Electron exchange between atoms:2 types of chemical bonds 1. Transfer of electron from one atom to another: Ionic bond 2. Two atoms share apair of electrons: Covalent bond (can be polar) Valence – number of electrons needed to fill the outermost shell Figure 2-5

12. Periodic table of elements Elements fall into groups with similar properties Figure 2-6

13. Covalent Bonds Form by the Sharing Electrons Shared electrons count as part of each atom’s valence shell Molecule is made of atoms held by covalent bonds Bond length: attractive and repulsive forces are in balance Bond strength: amount of energy needed to break the bond (kcal/mole) Multiple covalent bonds have definite spacial arrangements: bond angle, bond length, bond energy Figure 2-8

14. Different Types of Covalent Bonds Single Double • Single bond- sharing of 2 electrons • one donated by each atom • Double bond – sharing of 4 electrons • 2 donated by each atom: • shorter, stronger and more rigid • Polar bond – different atoms • attract shared electrons with different strength • Nonpolar– between the same atoms Figure 2-9 Polar Nonpolar Figure 2-10

15. Water Is the Most Abundant Substance in Cells • Water is the biological medium on Earth • All living organisms require water more than any other substance • Most cells are surrounded by water, and cells themselves are about 70-95% water • The abundance of water is the main reason the Earth is habitable

16. The water molecule is a polar molecule: The opposite ends have opposite charges • Polarity allows water molecules to form hydrogen bonds with each other Hydrophilic - molecules with polar bonds that can form hydrogen bonds with H2Oand will readily dissolve in water Hydrophobic – uncharged molecules that do not make hydrogen bonds with H2O

17. Four of water’s properties that facilitate an environment for life are: • 1. Cohesive behavior • 2. Ability to moderate temperature • 3. Expansion upon freezing • 4. Versatility as a solvent

18. Cohesion • Collectively, hydrogen bonds hold water molecules together, a phenomenon called cohesion • Cohesion helps the transport of water against gravity in plants • Adhesion is an attraction between different substances, for example, between water and plant cell walls

19. Some Polar Molecules Are Acids and Bases Chapter 2 Water is in a state of dynamic equilibrium in which water molecules dissociate at the same rate at which they are being reformed

20. Some Polar Molecules Are Acids and Bases Chapter 2 An acid is any substance that increases the H3O+ concentration of a solution A base is any substance that reduces the H3O+ concentration of a solution (raises OH- concentration) Figure 2-13

21. The pH Scale • The pH of a solution is defined by the negative logarithm of H+ concentration, written as pH = –log [H+] • For a neutral aqueous solution [H+] is 10–7 = –(–7) = 7