Problem Set 1

Problem Set 1 - Biology 131 Includes Problem Set 1 Summary...

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Biology 131 Includes Problem Set 1 Summary of lectures from first two weeks. The central roles of chemistry and physics in biology were emphasized. A number of important chemical principles were introduced. The electrical nature of matter was pointed out and the idea of an electric field was discussed. An electric field exists at a point in space if an electric charge placed at that point experiences a force. The interaction of atoms to form molecules via chemical bonds was discussed. Particularly, ionic, covalent and hydrogen bonds between atoms were examined. These ideas are covered in pp. 15 – 24 of Life , as well as in any chemistry text. The structure and properties of water were discussed. It was pointed out that the two hydrogen atoms form covalent bonds with oxygen to produce a water molecule. Hydrogen bonds between a hydrogen atom of one molecule and the oxygen atom of another stabilize water in the liquid state and contribute to its high specific heat and heat of vaporization. Water molecules are also polar; that is, a water molecule has some charge separation within the molecule, with the oxygen portion being electrically negative with respect to the hydrogen portions. This polarity of water makes it a powerful solvent for ionized atoms and molecules, as well as molecules that are electrically polarized like water itself. Non-polar molecules (examples later) dissolve poorly in water. (Refer to pp. 26- 28 in Life .) A certain fraction of water molecules are dissociated at any given time. They have lost a hydrogen ion (a proton), which can be considered to be free in the water. 2 HO H OH + ⎯⎯→ + ←⎯⎯ The concentration of hydrogen ions, H + , in pure water is 10 -7 M; that is there are 10 -7 x 6.02 x 10 23 hydrogen ions per liter of pure water. Because the hydrogen ion concentration in different solutions varies so enormously, it is useful to transform that concentration to another number called pH. The pH of a solution is defined as - log [H + ]. By the elementary rules of logarithms, the pH of pure water is 7 (-log10 -7 = 7). It should be understood that pH is not a different quantity from hydrogen ion concentration; it is just a different way of writing the same thing . When the pH of a solution is less than 7, the solution is said to be acidic and when the pH is greater than 7, it is said to be basic. An acid is a substance that causes the pH of a solution to decrease while a base causes the pH to increase. For example, CO 2 , which forms H 2 CO 3 when dissolved in water, is an acid. These ideas are discussed on pp. 28 –30 of Life . Carbon, hydrogen, nitrogen, oxygen, sulfur, and phosphorus are the most common atoms in the molecules of living organisms. Other atoms, such as calcium, potassium, sodium and chloride are present in the water phase of organisms and play important roles in physiology, but they are not integrated into the structure of macromolecules such as DNA, RNA, and proteins, although calcium especially has
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Problem Set 1 - Biology 131 Includes Problem Set 1 Summary...

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