J. A. CAMPBELL Harvey Mudd College Clarernont, California 91711
Questions Q220. "On the physiologist's usual time scale, urea behaves for manv cells as if it contributes nothine to the osmotic pressure of solutions." [A. V. Wolf, "Tgrst," C. C. Thomas, 19581. Why? Q221. Ionizing radiation, uv iight, mustard gas, and the nitrogen mustards are all powerful both as mutagenic and as carcinogenic agents. Suggest a possible generalized mechanism of their action. Q222. S. A. Waksman, e t al. [Ecology, 9 126 (1928)l reports some compositions of the fallen needle and buried humus layers in a pine forest. Arrange the chemicals in order of increasing "rotting rate" and calculate the relative rates of rotting of protein, lignin, and cellulose.
Needles Humus
Lignin 27.63 50.39
Cellulose 18.26 2.56
Hemi celluFats lose Protein Ash waxes 14.68 8.53 3.08 7.65 12.39 7.51 11.61 2 . 9 9
6223.
Cell division may be written as
1 cell + nutrient = 2 cells nutrient = cell +waste
+ waste, or
since the first cell emerges unchanged (it is a catalyst). Comment on the thermodynamics of cell production. The experimental enthalpy loss [Bayne-Jones, S., and Rhees, R. S., J. Bacterial., 17 123 (1939)l is 2400 callgm for E. colt. How does this relate to your argument?
This column consists of questions (plus possible, but certainly not uniquely satisfactory, answers) requiring no more than a concurrent first-year, college level course,a data handbook, and a willingness to apply fundamental chemical ideas to the systems which surround us (or even are inside us). Contributions for possible inclusion are solicited. Initiated in the January, 1972 issue of this Journal.
Answers A220. Urea, HrNCONHz, is a relatively small, water-soluble molecule which probably can diffuse through many cell walls, though not as fast as does water. If urea is generated slowly it will so diffuse and contribute almost nothing to the osmotic pressure effects since there is such a small concentration gradient of urea across the membrane. A221. Both ionizing radiation and uv light can convert H 2 0 (the most common cell constituent by far) into reactive substances such as H. OH, H102, HOr, etc. Hydrolysis of the mustards mieht form the same molecules or ~ e r h a n sthe mustards themselves act similarly, attacking the nucleoside links, causing breaks in one of the DNA spirals and producing useless or nonsense genes when the spiral unwinds and proceeds toward forming RNA. T h e breaks are probably produced by regular chemical reactions, not directly by the radiations which are much mare apt to interset with the abundant water in the eell than they are with the DNA during their brief passage through the eell. A222. Everything except the ash rots so assume the amount of ash r e m a i n constant, that it is not leached out by the water. Now calculate all the concentrations relative to ash. Then take the fsstest rotting rate (biggest ehangr of relative eoncentratirm) and divide it into all the other changes to get relative rotting rates.
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48 / Journal of Chemical Education
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This assumes rotting rate is independent of amount present, and gives very similar rates for all the materials. A223. For the reaction: nutrient = cell waste, AH = -2400 callg. Cells clearly seem to he of lower entropy than nutrient, a n d waste of higher entropy. T h e reaction occurs, so AG must be -. Let's estimate AS for the reaction. T h e minimum value of I G is zero which will give the maximum negative value of I S fur the reaction, since AH = TAS under these conditions: I S = AHIT = -2400 lcal/g)/310 K = -7.8 calllg X K). Since I S fur nutrient to waste is positive, AS for nutrient to eell must be more negative than this -7.8 cal/(g X K ) which is already a large negative value compared to entropy changes for other processes. For example, the condensation of a gas to a liquid is about -0.2 calllg X K), for many substances. Actually, for a cell to form, AG must be
