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Unformatted text preview: C HAPTER 1- B IOCHEMISTRY : A N E VOLVING S CIENCE Biochemistry is the study of the chemistry of life processes. Biochemical unity underlies biological diversity; cells are a key unifying feature that underlies this diversity. Deoxyribonucleic acid (DNA) stores genetic information in all cellular organisms. Proteins, the macromolecules that are key participants in most biological processes, are built from a set of 20 building blocks that are the same in all organisms. The similarities among different organisms suggest that all living things on Earth have a common ancestor and that modern organisms have evolved from this ancestor into their present forms. Biological challenges are solved at the biochemical level; in most cases, these challenges are addressed by the adaptation of existing macromolecules to new roles rather than by the evolution of entirely new ones. DNA illustrates the interplay between form and function. DNA in a linear polymer made up of four different types of monomers (monomer = one sugar- phosphate unit and one of the four bases attached to the sugar); it has a fixed backbone built of repeating sugar-phosphate units. Each sugar is connected to two phosphate groups and orientated in the same way causing each DNA strand to be polar, with one end distinguishable from the other. DNA has four base pairs (Adenine, Cytosine, Guanine, and Thymine). Two single strands of DNA combine to form a double helix, running in opposite directions with respect to the axis of the double helix. The key to this structure is that the bases form specific base pairs held together by hydrogen bonds: adenine pairs with thymine (A-T), and guanine pairs with cytosine (G-C). Hydrogen bond are much weaker than covalent bonds, but such weak bonds are crucial to biochemical systems; they are weak enough to be reversibly broken in processes, yet they are strong enough, when many form simultaneously, to help stabilize specific structures such as the double helix. Connection between form and function: The structure is compatible with any sequence of bases, and because the base pairs have essentially the same shape, they fit equally well into the center of the double-helical structure of any sequence. This sequence of bases is how genetic information is stored. Moreover, if the DNA is separated into two separate strands, each strand can act as a template for the generation of its partner strand through specific base-pair information. Concepts from chemistry explain the properties of biological molecules. The double helix can form spontaneously from its component strands. Covalent and noncovalent bonds are important for the structure and stability of biological molecules....
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This note was uploaded on 04/01/2008 for the course BIOLCHEM 415/515 taught by Professor Ballou during the Winter '08 term at University of Michigan.
- Winter '08