J. A. CAMPBELL H - n e y Mudd College Clarsrnrnt, Cdifornia 9171 1
Questions 6229. Insulin, natural or synthetic, cures diabetes. I t is generally recognized t h a t a major symptom of diabetes is a high concentration of glucose (one of t h e main sources of body energy) in t h e blood. It is n o t so generally recognized t h a t most of t h e other symptoms of diahetes are identical with those d u e t o starvation. T h u s a diabetic is starving though bathed in a sea of food. Suggest a possible physiologic role for insulin. 6230. T h e standard free energy change for t h e reaction ATP"
+ H30 = ADP" + HH,PO,-
is -5.9 kcallmole whereas t h e value found for t h e actual free energy change in frog muscle for this reaction is -9.4 kcallmole. [Podolsky, R. J., a n d Morales, M . F., J. Biol. Chem., 218 945 (1956)]. Suggest interpretations of this difference. 6231. Don J u a n P o n d in t h e Wright Valley of Antarctica freezes a t -57'C. Suggest a specific chemical interpretation. [Tedrow, J. C. F., e t al., N. Zealand J. of Sci., 6 150 flQfi?\ l , 6232. Winemaking is often helped b y adding 4 g (NH4)2S04, 0.5 g MgS04, a n d 2 g K3POa per 8 1 of juice t o
-,.,
which yeast has been added. Suggest a probable function of each of t h e added salts. Q233. T h e flour mite Aearus siro cannot survive if t h e temperature exceeds t h e range of 0-31-C a n d t h e humidity falls below 60%. Sucsest -- chemical interpretations of these limits. 6234. Iron (in ionic form) is a common (and possibly t h e only) necessary co-factor for enzymes (phenolytic dioxygenases) which catalyze t h e addition of both atoms of one molecule of oxygen into a single phenolic molecule. Discuss possible mechanisms i n terms of t h e electron structures of iron ions and 0% molecules. How d o you interpret t h e fact t h a t all b u t one of these iron-containing phenolytic dioxygenases is colorless. -
This column consists of questions (plus possible, hut 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 inelusion are solicited. Initiated in the January, 1972 issue of this Journal.
Answers
tiate andlor maintain glucose consumption. Thus, it is not sufficient that glucose be present in the blood, it must also reach the sites where it can react and then must react if it is to supply enerev. Insulin helm control this rate.
tissue. The relationship is
AG = AG"
[H,PO,-1 + RT in [ADP'-] [ATP3-] [H1O1 -
Since AG is more negative than AGO, the ratio inside the In term must be smaller than one (relatively less ADP andlor HzP04-) in the actual system compared to the standard state. A231. A highly soluble (probably highly dissociated) molecule must be present in the water. The total molality of ions must be about 37PC/1.860C -- 20, or 20 moles of particles per 1000 g of lake. A 1-1 electrolyte would have to he about 10 M, and a 1-2 electrolyte (dissociated) about 7 M. There are few ionic substances common enough to be possibilities. NaCl is t h e most obvious but its maximum solubility is about 5 M. The actual component, according to Tedrow, is CaC12. A232. (NH&S04 provides potential-NHs groups for amino acid and orotein svnthesis olus some S for the sulfide erouos
188 / Journal of Chemical Education
t e p s . K . P & provides PO4 tu k w p the .4TP-f\1)I' zyclc zoing (and s~mnlsrryclrsr and 11, allon gene synthe& including DNA and the various HYA's. Konc of these three supplws mwh en. ergy, as such. Rather they give atoms and groups required in the synthesis if the cells are not to begin to cannibalize themselves. A233. At low temperature (below 0%) rates of physiological reaction become too small to maintain the mite. At high temperatures (above 3I0C) enzymes (and other physiological molecules) decompose more rapidly than then can be synthesized and the physiological system breaks down. Below a humidity of 6 W dehydration of the mite occurs and death follows. A234. Fe"+ has its 3d level half full (5 unpaired electrons) with all lower levels full. 0 2 has 2 unpaired electrons per molecule thus can form a bond to Fe3+ using one of the 3d levels. The 0 2 would probably sit on the Fe-0-0 with the outer axygens still having an unpaired electron which should be reactive toward addition with a phenol. The iron ion is no doubt coordinated to the enzyme through N: or 0: electron pairs, probably octahedrally. This gives a high spin configuration, like Fel,,,2+ with d.'dY2. Aa is 35 kcallmole which is just outside the visible on the red end of the spectrum so the complex is colorless. (Remember, however, that the iron ion in hemoglobin also holds onto 0 2 molecule^ and is octahedrally coordinated but gives a deep red color, suggesting that its Aa is about 60 kcallmole, ahsorbing in the blue. The smaller Ao value in Fez+ and the dioxygenases indicates a smaller d, - d, gap and, therefore, weaker attraction between the iron nucleus and its 3d electrons than in hernog1obin.l
