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Unformatted text preview: Chapter 2. Chemical Foundations. Four most important bonds forming weaker noncovalent interactions: 1) Hydrogen bond 2) Ionic interactions 3) Hydrophobic bonds 4) Van der Waals interactions Covalent bonds- hold atoms together have strongest energy associated with sharing of electrons in atomic orbitals. These bonds are major determinant in 3-D shape and chemical reactivity of molecules. Most organic molecules in living systems contain 6-different atoms: H 2 , C, N, P, O, S. Atoms form covalent bonds dependent on the number of electrons needed to fill outer orbitals: e.g. H has 1 electron and forms H 2 ; C has 4 electrons usually forms 4-bonds CH 4 ; N has 5 electrons in outer orbital usually forms 4 bonds as in ammonium ion NH 4 . Phosphorous, P can form five bonds as in phosphoric acid H 3 PO 4 (a resonance hybrid, a structure between two forms). Esters (double bond to O) of phosphoric acid form backbone of nucleic acids. 2.2 Chemical Building blocks of Cells Three most abundant biological macromolecules proteins, nucleic acids, and polysaccharides are all polymers composed of multiple covalently linked identical or nearly so, small molecules or monomers (Fig 2.11). Covalent bonds between monomers usually are formed by dehydration reactions in which a water molecule is lost. Phospholipids assemble noncovalently to form a two-layered bilayer structure, the basis of all cellular membranes. Proteins- strings of ten to thousands of amino acids linked by peptide bonds. Nucleic acids are linear polymers of nucleotides linked by phosphodiester bonds. Polysacharides are linear or branched polymers of monosacharides such as glucose linked by glycosidic bonds. Proteins: Monomeric building blocks of proteins are 20 amino acids all of which consist of a central α carbon bonded to four different chemical groups: an amino group (NH 2 ), a carboxyl group (COOH), a hydrogen atom (H) and one variable group called a side chain or R-group. Four Different Nucleotides are used to build Nucleic Acids. Two types of chemically similar nucleic acids DNA and RNA are the principal information carrying molecules of the cell. Monomers from which they are built are called nucleotides and have a common structure, a phosphate group linked by a phosphoester bond to a pentose that is linked to a nitrogen and carbon containing ring structure referred to as the base (Fig 2.14). The bases adenine, guanine, and cytosine are present in both DNA and RNA. Thymine is found only in DNA and uracil is found only 1 in RNA. Adenine and guanine are purines containing a pair of fused rings; cytosine, thymine, and uracil are pyramidines with a single ring (Fig 2.15). Carbohydrates; are constructed of C (carbo), plus H and O (hydrate-water). Simplest are monosacharides which is CH 2 O n where n = 3,4,5,6 or 7. All monosacharides contain an aldehyde or keto group....
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This note was uploaded on 09/18/2008 for the course BIM 202 taught by Professor Simon during the Spring '06 term at UC Davis.
- Spring '06