J. A. CAMPBELL H o n e y Mudd
College
Cloramat, California 9171 1
Questions s resniraQ257. Resniration includes a series of s t e ~(the tory chain) of varying redox potentials: 0 2 = 0.8V to DI'N = -0.3 V. Cvtochrome a an. . , h.. c.. and ct have wtentials of 0.28. 0.07,0.23and 0.21, respectively. In what sequence in the res: piratory chain do these cytochromes act as they sequentially carry H atoms from DPNH toward Oz and eventual formation of Hz07 Q25R. The rate of oxygen consumption by many sea animals is independent of the concentration of dissolved oxvnen except a t lo& values. Is diffusion of oxygen from sea wate; to t h e gill . surface apt to he a rate-determining.step . in oxygen .. consumption? Q259. J. D. Watson ["Molecular Biology of the Gene," W. A. Benjamin, New York, 19651 notes that "The general rule exists that &@ (ADP) is released in almost all biosynthetic reactions. Almost as soon as it is made, it is enzymatically thereby making impossible a reversal broken down into 2 0, of the biosynthetic reaction." How does this fit in with the observation that ATP not ADP, is the normal dire& energy donor in biochemistry? 6260. Many hacteria can be preserved as freeze-dried cultures ~ . r e.n a r e dbv. ranid . evacuation and simultaneous cooling. This is murh less damaging than freezing in solution, hut e\,en that orocrsi i i often not IOO'b lethal i f the freezine is done rapidl; and the reheating is done slowly. Suggest &
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effect which makes these methods less lethal than slow cooline and rapid heating. Q261. R. L. Cleveland exnerimented exteusivelv with termites [Biol. Bull. ~ o o d s ~ o i48, e , (1925;54, (1928);~uai-t. Rev. Biol.. 1. (1926)l. He discovered: (1) adult termites can live indefinitely on pure~celluloseand air, (2) four speci of flagellate protozoans swarm in termite gut, (3) each species of flagellate can be killed selectively by suitable combinations of incuhatinn the termites a t 36'C for 24 hours, totally fasting the term&, or varying the ambient Oz pressure from norma up to 35 atm for varying lengths of time, (4) termites die rapidly if all flagellates are killed, (5)two species of flagellates can be seen to ingest and digest cellulose and a t least one of these species must be present if the termites are to live, (6) numerous freeliving hacteria which fix nitrogen are found in the gut. Use chemical arguments to suggest probably symbiotic relationships between the four groups: bacteria, flagellates digesting cellulose, flagellates not digesting cellulose, and termites. This column consists of questions (plus pnssible, but certainly not uniquely satisfactory,answers) requiringnomore thanaconcurrent first-vear. . . colleee .. level course. a data handbook. and a willineness .. to nppls fundamental Ihcm~rnlidens mrhr iy%trmswhich surnmnll us t l w wen a r t inode M I .Cuntributiuni fur pukble inclu&n are so1ititt.d. Initiated in the .lanunry, 1972 issue ofrlrl*Jotrrntll. ~
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Answers A257. Assuming the concentrationsm e such that ht8 quowd represent actual vulta~estn wva, the half reactions must line u p in order of decreasing oxidation potentials: O2(O.H),a + ri,10.2R).e 10.2RI.cl 10711, b 10.071.DPN (-0.3,. H iscaniedfrom DPN to O2thmuph the reverse of this sequence A258. If the rate of consumption of a reactant is independent of its concentration, there must he a rate-determining step in which that readant is not involved. Thus the diffusion of O2in the gills offish must be fast compared to some other step not involving 02.
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A259. The reaction ATP ADP Pis coupled to other reactions in the production of energy, probably by way of enzymes. Maximum use of energy occurs if the driving force (AG or 6 ) is keot small. This means the concentrationsshould not be far from thr equilibrium set under usual physwlc+4 reaction conditions. Vnder these rireumstnneea the renrtimr will reverse if sume concentrationsget a little higher or lower. However, if ADP iseffectively rcmuvrd by a competing followng r~nrtion,tpresumnhly especially when itsconcentrarionstnrts torire1 theA'r1'roupled reaction will continue rather than reverse. Thus. rheA'1'1' AD1' reaction is kinetically controlled and only occ& when the rest of the coupled system is available for reaction, the ADP then reacting further ss indicated. It would he highly desirable to synthesize ATP from AMP by a quite separate mechanism which did not produce free ADP, so minimizing the chance of reversing the coupled system.
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LADp reactant
Schematic: ATP
I
pmduct
ADP f
AMP
X
Y
An even simpler mechan~zmuould he to have ADPgudirertly to ADP.); rather than AMP. Presumably this i.; barred uy kinetic
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A260. Slow freezing formslarge ice crystals which disrupt the cells. Rapid freezing keeps the water near its active sites in the cells and does not leave large ice enistals. Slow thawing allows the water to return to the activesizes where it is needed before T rises to the place where enzyme activity is rapid. The system becomes fluid and aqueous before metabolism gets fully underway with slow warming. A261. Termites ingest cellulose and air hut cannot digest either alone. Two of the flagellates digest cellulose hut cannot generate protein from N? in air and get no protein from the cellulose ingested by the termite. Two flagellates digest cellulose to saecharides which termites and bacteria can use, the latter generating amino acids from N, in the air and the saccharides. The termites fin" the rellulose and air then feed un the products produced hy the bacteria and twu d t h c flagellaws As far ay the dab $h
