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Chapter 2 - Bio 20A-M Dalbey Assigned Reading The Chemistry...

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Bio 20A-M. Dalbey The Chemistry of Life (Chapter 2) 3/29/08 1 of 5 Assigned Reading: Chapter 2 Sections 2.1 (p. 21) 2.2 (p. 25) 2.3 (p. 30) 2.1 What are the Chemical Elements the Make Up Living Organisms? p. 21 Element % composition as # atoms in dry weight of a typical cell H 54.33 C 28.55 O 8.57 N 6.85 P 0.66 Na* 0.30 S 0.21 K* 0.18 Mg* 0.14 Cl* 0.10 Ca* 0.09 Fe 0.02 SUM 99.98 The point of this is that the relative abundance of (most) chemical elements in biomass reflects their participation in the covalent structures of the major classes of the biomolecules which we soon encounter in Chap. 3. Other chemical elements (denoted by *) are present as ions in solution and usually not as part of organic molecules. The table below summarizes the elemental composition of the major classes of biomolecule. Proteins (Amino Acids) Nucleic Acids (Nucleotides) Sugars Lipids H x x x x C x x x x O x x x x N x x x x P x "x" S x x = always present "x" = often present You should come back and review this table again after we cover Chapters 3. The term " atomic mass" is synonymous with what I learned as " atomic weight" . I will probably use the latter term by force of habit although it is technically inappropriate. By the same token I generally use " molecular weight" rather than " molecular mass" .
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Bio 20A-M. Dalbey The Chemistry of Life (Chapter 2) 3/29/08 2 of 5 Isotopes The radioactive (ie. unstable) isotopes used most frequently as "tracers" in biology are: 3 H ("tritium") 14 C 32 P and 33 P 35 S 2.2 How do Atoms bond to Form Molecules? p. 25 Summary of Chemical Bonding Forces: Covalent Bond (IMPORTANT) Hydrogen Bond (IMPORTANT) Ionic Bond "Hydrophobic Interactions" van der Waals Forces Example: H• + H• ---> H:H = H-H = H 2
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