You’ll never find an easier, more efficient, and more focused way to ace biochemistry and biochemistry-related questions on the USMLE and course examinations than the USMLE Road Map . Designed to provide maximum learning in minimum time, this fully updated USMLE Road Map offers a concise, creative, and well-illustrated approach to mastering biochemistry.
I. Water A. The special chemical properties of water make it ideal as the main physiologic solvent for polar substances in the body. 1. Within the water molecule, the oxygen nucleus draws electrons away from the hydrogen atoms, producing an internal charge separation that makes each molecule magnetic or polar. 2. Substances that dissolve well in water are referred to as polar or hydrophilic. 3. Molecules that dissolve sparingly in water are nonpolar or hydrophobic. B. Water molecules bind with each other through important noncovalent interactions called hydrogen bonds. 1. Hydrogen bonds result from attraction between the partially positively charged hydrogen atoms of one molecule and the electronegative atom, usually oxygen or nitrogen, of another molecule. 2. Hydrogen bonds are weak and rapidly break and re-form up to 1012 times per second in water at 25°C. C. The hydrogen bond network of water molecules confers special properties on water that are important for sustaining life. 1. Water has a high surface tension where it comes in contact with air. a. Surface tension is the force acting to push together the liquid molecules at an air-liquid interface. b. This property causes the liquid to form droplets and to resist passage of substances across the interface. c. The surface tension of fluid at the alveolar air-water interface of the lungs contributes to elastic recoil that causes the alveoli to return to the original volume after inflation during breathing. 2. Water has a high heat of vaporization, ie, the amount of heat needed to convert from liquid to gas phase. In conjunction with its high heat capacity, this property allows water to carry away heat efficiently as it evaporates, which accounts for the cooling effects of perspiration. 3. Water has a high dielectric constant, which is a measure of its ability to carry electrical current, as it does in nerve cells.
Dr. Abdullah is a professor and a doctor teaching students to get there med license.
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