Lecture 2 (Aug 31)

Lecture 2 (Aug 31) - Biological Sciences 110A: Introduction...

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Unformatted text preview: Biological Sciences 110A: Introduction to Biology Kendal Broadie Lecture 2 . The chemistry and composition of cells: elements, bonds, and water Primary elemental composition of cells Brief review of atomic structure: electron shells Covalent bonds between atoms (shared electrons) Ionic bonds between atoms (opposites attract) Weak bonds: van der Walls force (atomic attraction) Carbon-based life: carbon bonding interactions Aqueous cell environment: water and hydrogen bonds Reading in Chapter 2 (31-42) Karp The chemistry of cells: A primer Restricted to a small subset of elements Dominated by the chemistry of carbon Biochemical reactions occur over a narrow temperature range (~0-100 o C) Dominated by macromolecules and polymers (-X-X-X-X-) Reactions are facilitated by protein catalysts: enzymes Reactions are often spatially localized to a specific cell surface or compartment Three elements comprise >95% of the atoms in living cells ~24% 16 8 8 8 ~1% 14 7 7 7 N ~24% 12 6 6 6 C ~48% 1 1 1 H % Mass #N #e- #P Atomic number <0.5 35 18 17 17 Cl <0.5 39 20 19 19 K <0.5 40 20 20 20 Ca <0.5 32 16 16 16 S <0.5 31 16 15 15 P <0.5 24 12 12 12 Mg <0.5 23 12 11 11 Na Relative abundance (%) 50 40 30 20 10 Organisms Earths crust etc Ca & Mg Na & K P N H C O Si Protons: + charge (+1. 2 x 10-27 kg; 3 x 10-15 m) Electrons: - charge (1. 9 x 10-31 kg; 1.5 x 10-16 m) Protons, neutrons, and electrons: A review of atomic structure Diameter of a typical atom ~0.1-0.3 nm . e- Common isotope of hydrogen has a single proton and electron Mass of H atom = 1 dalton Neutrons: no charge (0. 2 x 10-27 kg; 3 x 10-15 m) Electron shell (orbital, cloud) The innermost shell (I) can contain a single pair (2) electrons. Shell II can contain four pairs (8) electrons. Protons, neutrons, and electrons: A review of atomic structure . e- . e- The electron shell of noble (inert) gases are filled Example: Helium has 2 electrons, so the first electron shell is filled Each electron shell accommodates a maximum number of electrons in orbit around the atomic nucleus....
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Lecture 2 (Aug 31) - Biological Sciences 110A: Introduction...

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