2. Reading assignments Nelson: purple pages F3 through F34 Cooper: chapter 2 How to do: 1.Go over slides first and your class notes a)Are there some concepts unclear to you? b)Did you raise some questions? 2.Selectively read through book and complete your notes 3.Rehears your learning using slides as a platform 4.Try out assigned interactive modules 5.Test yourself using “Self Quiz” questions on the website 6.Take time-sensitive on-line test quiz

3. Cell Biology: Why to Study the Cell? Life forms are complex and diverse Cell: Structural and functional unit of life Cells obey the same laws of chemistry and physics that determine the behavior of nonliving systems Modern cell biology seeks to understand cellular processes in terms of chemical and physical interactions Question: What are the cells composed of?

4. Matter: composed of elements Elements: pure substances composed of one type of atom – Out of 94 natural elements, cells are made primarily of six major elements C, H, N, O, P and S (98% of body weight) – Others (<1%) : single ions Na +, K +, Mg 2+, Ca 2+, Cl - CHNOPS: incorporated into organic molecules

5. Molecule: two or more atoms bond together to form a molecule (NaCl, H 2, CH 4..) Compound: molecule composed of more than one type of element (NaCl, H 2 SO 4, H 2 O…) Chemical bonds: form by exchanging the outer layer electrons between two or more atoms The electrons in the outer valence shell determine the chemical reactivity of atoms

6. Atoms might lose, accept or share electrons in valence shell In atoms with two or more shells, chemical reaction completes the number of electrons to 8 (octet rule) Chemical bonds – Ionic: complete loss or gain of one electron, negative or positive ions – Covalent: electrons are shared between two atoms

7. More electron negative Cl atom attracts an electron and Na loses an e - Negatively charged (Chloride Anion) & positively charged (Sodium Cation) interact electrostatically to form Ionic bond Salt: organized crystals when saturated or at low temperature Na Cl Na + Cl - Sodium Chloride (NaCl)

8. Covalent bond: forms when two atoms complete their valence shells by sharing electrons Example, Methane: the 4 valence electrons, equal energy levels, in SP3 hybrid orbitals completed by sharing with 4 electrons of four H atoms Non polar, tetrahedral Angel 109 degrees

9. Electronic configuration in C makes it possible to form covalent bonds with other elements Bonding with another Carbon – Linear, branched or cyclic C backbone chains – Result in almost unlimited diversity of molecules Covalent bonding with elements other than carbon – Reult s in Important functional groups Practice: Try to draw structural models for each functional group. Show the carbon to which the group is attached and the shared electrons

10. Water The most abundant molecule on the earth 3/4 of globe’s surface is covered by water Comprises 70-90% of total cell mass Water molecule: Oxygen’s 2 valence electrons shared with 1 e of two H Planar molecule, asymmetric, unequal electron distribution 2 pairs of unshared electrons Oxygen strong electronegativity Molecule is polar 104.5 ˚

11. Properties of water Hydrogen bond: Strong polarity ->Hydrogen bonds (~5 kcal/mole) σ+ and σ - dipoles attracted Aqueous phase: average ~3 hydrogen bonds per molecule Forms interconnected water lattice, less ordered Solid phase (ice): 4 hydrogen bond/molecule, rigid bonding and ordered Intermolecular spacing increased (volume expansion) -> lower density-> floatingspacing increased Imagine what would happen if ice could sink? Water lattice

12. Properties of water Water as Solvent: for polar molecules and molecules with ionic bonds salts (hydrophilic) –Non-polar moleculs (hydrophobic) are not soluable or poorly soluble in water Dipole-dipole interactions form a hydration shell around hydrophilic molecules Dispersion of ions and molecules in water=dissolving Water=Solvent; dissolved molecules=solute Biological importance: –Water bridge in macromolecules stabilizes structure –All biochemical reactions require aqueous environment Fig. 3.7, Campbell & Reece, 2002

13. Properties of water Cohesion: hydrogen bonding btw water molecules hold them together; this is Cohesion Adhesion: hydrogen bonding with other molecules makes water stick to other objects –Cohesion and adhesion cause water rise in xyleme fibrils in plants; resist gravity -> continuous flow High heat capacity: 1 cal/g raises temp 1 ˚ C, almost twice as others –As a result water has high boiling temperature (100 ˚ C) –Water resists fast evaporation and cells can resist drying in a wide temperature span Watch summary movie

14. Can you meet these objectives? Discuss the importance of carbon in cell chemistry? Describe and compare the chemical bonds? Describe the key characteristics of water?