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Chapter_02_Solutions

Chapter_02_Solutions - Chapter 2 Cells Chemistry and...

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THE CHEMICAL COMPONENTS OF A CELL DEFINITIONS 2–1 Avogadro’s number 2–2 Hydrophobic force 2–3 Molecule 2–4 Atomic weight 2–5 Hydrogen bond 2–6 Acid 2–7 van der Waals attraction TRUE/FALSE 2–8 True. With each half-life, half the remaining radioactivity decays. After 10 half-lives (1/2) 10 , about 1/1000 (exactly 1/1024) of the original radioactivity will remain. (It is useful to remember that 2 10 is about 1000.) 2–9 False. The pH of the solution will be very nearly neutral, essentially pH 7, because the few H + ions contributed by HCl will be outnumbered by the H + ions from dissociation of water. No matter how much a strong acid is diluted it can never give rise to a basic solution. In fact, calculations that take into account both sources of H + ions and also the effects on the dissociation of water give a pH of 6.98 for a 10 –8 M solution of HCl. 2–10 False. Strong acids bind protons weakly and give them up readily in a water environment. 2–11 False. Many of the functions that macromolecules perform rely on their abil- ity to associate and dissociate readily, which would not be possible if they were linked by covalent bonds. By linking their macromolecules noncovalently, cells can, for example, quickly remodel their interior when they move or divide, and easily transport components from one organelle to another. It should be noted that some macromolecules are linked by covalent bonds. This occurs primarily in situations where extreme structural stability is required, such as in the cell walls of many bacteria, fungi, and plants, and in the extra- cellular matrix that provides the structural support for most animal cells. THOUGHT PROBLEMS 2–12 Organic chemistry in laboratories—even the very best—is rarely carried out in a water environment because of low solubility of some components and because water is reactive and usually competes with the intended reaction. In This Chapter THE CHEMICAL A13 COMPONENTS OF A CELL CATALYSIS AND THE A27 USE OF ENERGY BY CELLS HOW CELLS OBTAIN A34 ENERGY FROM FOOD A13 Chapter 2 2 Cells Chemistry and Biosynthesis
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A14 Chapter 2: Cell Chemistry and Biosynthesis The most dramatic difference, however, is the complexity. It is critical in lab- oratory organic chemistry to use pure components to ensure a high yield of the intended product. By contrast, living cells carry out thousands of differ- ent reactions simultaneously with good yield and virtually no interference between reactions. The key, of course, is that cells use enzyme catalysts, which bind substrate molecules in an active site, where they are isolated from the rest of the environment. There the reactivity of individual atoms can be manipulated to encourage the correct reaction. It is the ability of enzymes to provide such special environments—miniature reaction cham- bers—that allows the cell to carry out an enormous number of reactions simultaneously without cross talk between them.
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