I J. A. CAMPBELL H.ney Mudd Cdlsg. C l a r a r n ~ t ,California 91711
Questions Q247. Sidney F o x a n d colleagues [Science, 132, 200 (1960)] have heated mixtures of 18 d r y amino acids with phosphoric acid a n d obtained amino acid polymers u p to 10,000 in molecular weight. T h e s e polymers a r e degraded by proteolytic enzymes, have nutritive value for bacteria, and are n o t antigenic. W h y d o you suppose s u c h experiments a r e undertaken a n d w h a t meaning d o t h e y have t o you? Q248. How long m u s t a D N A section h e which codes t h e formation of a protein containing 200 amino acid units? S u c h a u n i t i s called a cistron. 6249. D e e p p o n d s a n d lakes often "overturn" as winter g e t s colder, exchanging their top a n d bottom waters "spontaneously." Interpret. Would you expect t h e m to continue t h e overturns as spring approaches? 6250. B o t h m a n and frog use t h e fumarase catalyzed reaction, fumarate2H z 0 = malate2-, in a n i m p o r t a n t physiological cycle. I n vitro experiments at 25OC give values
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of AGO = -880 caumole a n d AHD = -3,560 cal/mole. Calcul a t e A G O for man: also for a froe o n an earlv -s ~. r i n dea v when t = T C .Any comment? 6251. Assume t h a t only hydrogen bonds of energy 6 kcallmole were responsible for t h e "informational structure" in cell reproduction. W h a t is t h e Q priori chance of a n error in synthesis a t a given b o n d ? l s this likely? [M. J. Morowitz i n "Progress in Theoretical Biology," F. M. Snell, (Editor), Academic Press, New York, 19671.
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I his rrdumn conria& uf questlrnx lylus pwiblr, hut certainly not uniquely r;stisfactory,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
A247. The source of proteins is a major cosmological and hiological problem. Fox's work suggests they form readily from amino acids and phosphoric acid (both known to have been synthesizable when the earth was hotter and devoid of living systems). Over long periods of time many proteins could farm in this way and be available for aggregation into cells, organisms, and individuals. It is certainly interesting that the proteinaceous material he found in vitro is not harmful to present life farms. A248. 200 amino acid unita require 3 X (200 + 2) 6W nucleic acid units in the DNA cistran coding for it. Since one nucleic acid segment is about 0.34 nm thick along the spiral, the total length of the spiral is about 600 X 0.34 = 200 nm. If the chain were to be stretched out "straight," it would, of course, be Longer. A249. At the temperature of maximum density (4'C) water will sink in either colder or hotter water. Thus. as winter sets in. fhe upper water tends tosink tothe hottom nnt~lrheluwm waters haw a tmqxraturo ot.tDC Nl>such process occurs in the spring as the top water warms. However, light does penetrate, debris settles from top to bottom, and rotting of organic matter occurs on the bottom. All tend to warm the hottom, sometimes enough to cause an overturn in the spring of warmer bottom and colder surface waters. AG-AH A250. d(AC)ldt = ----
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T
(assume all terms constant over a short interval in T) = [-880
surroundings. The value of AGO becomes more negative as the frog cools increasing the tendency of the reaction to occur and, probably, partially offsetting the decrease in rate which occurs on cooling. In other words, there will be less reaction per unit of time hut each molecule reacting can do more work since AGO is more negativeat the lower T. Man is warm-blooded and essentially at constant T so his svstem is adiusted to the reaction rate nnd AG value for body T (almost invariant in time). Note that ASoZs8= [AHo- AGo]IT = [-3560 - (-880)]1298 = -9.00 cal/(mole X K) as might be expected since two moles of reactant form one mole of product. A251. Use Boltzmann equation to calculate chance of bond breaking.
- (-3560)](cal/mole)l298
For man: ACD3~o K = -880
For frog: A G O m=~ -880
K = 9.00 cal/(mole
X
K)
+ (37 - 25) 9.00 = -772 callmole + (7 - 25) 9.00 = -1042 cal/mole
assuming the frog is a cold-blooded animal isothermal with his
Thus there ii a rhnncc oferror better than I in ID', much too h i ~ h tor reliability There must be stronger iurws acting coproduce the ~ntcmmtiamc hain. 'There are n b u t I0"colb in n human SUDDOS~ each cell contains 1013 atoms and can survive 100 errors. Then (Actually this is pessimistic repraducihility should be about since most molecules are H20 and "errors" there quickly heal themselves. On the other hand, we have not specified a time interval so shall assume these two factors cancel one another. To requires a bond strength of about 30 have an error factor of (kcallmole) or more. Thus the sequential bonds which carry the information should be covalent ones, as indeed they are. The crass linked bonds can be much weaker (in fact thev must be in order to form and take m a r t the soirals) for their chance of correct trnnsferrsl of inio&tion is &tlg enhanced I.). the ~eomctrical restr~ctronaf w e d by the itrong covalent bun&
soz5.
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Volume 53. Number 7. July 1976 / 447
