Müller I. A history of thermodynamics. The doctrine of energy and entropy (Müller I. A history of thermodynamics. The doctrine of energy and entropy.pdf), страница 72

Chap. 4. Such a statement must be qualified,at least as far as animal life is concerned.12 Indeed, one of the functions oflife is the decomposition of glucose and that increases entropy as we sawabove. Doubtless the decompositions of fatty acids and amino acids are thesame in that respect, although I lack numbers for those cases.It is true, however, that the decomposition of glucose in the tissue isaccompanied by anabolism, which is also a function of life. Like whenglucose builds glucose phosphate and then glycogen. We have seen thatthe assiduous ATP’s carry their energy to the site of construction of glucosephosphate and we have implied that glycogen and glucose phosphate areenergetically on the same level. Thus the two reactions involved maybe written as(I)(I)Glucose + ATP ĺ glucose phosphate + ADP + ǻhR with ǻhR < 0n × glucose phosphate ĺ glycogen + n × phosphoric acid + ǻhR (II)(II)with ǻhR = 0.Of course, one may ask why step (I) and step (II) occur at all.

Why is theglucose ļ glycogen balance not simply maintained by mass action viahydrolysis and condensation? And what about the entropy change of thereaction? It seems likely that entropy decreases – because order is createdby the build-up of the long glycogen chain – but again I lack numbers.13 Ifindeed entropy decreases, it must be that ǻhR(I) has a sufficiently largenegative value, – i.e. the reaction (I) is exothermic to a large degree – inorder to offset the entropy drop so that the free energy can decrease, as itmust.It seems to me that it might be worthwhile to study the thermodynamicsof anabolism with an eye on the energies of reaction and the entropies ofreaction. This may not actually teach us more about the reactions than wealready know; but it may explain why a particular reaction occurs ratherthan another, seemingly simpler one.On the other hand, the people, who disentangled the complex workingsof intermediary metabolism, were probably not much concerned withthermodynamic questions.

Even without that concern it must be admittedthat they did an excellent job. Nor did they go unrecognised. Nearly all ofthose biochemists whom I have mentioned received the Nobel prize:Wieland, Warburg, Krebs, Lipman, Pauling,14 and the Coris. The Germans12We shall come to plant life in a short while.Those books which I have consulted for the writing of this chapter do not give entropiesfor such molecules as glucose phosphate and glycogen chains.14 Pauling is one of only two persons who received two Nobel prizes, – one for peace,because of his commitment against nuclear armament. The other person with two prizes isMarie Sklodowska Curie (1867–1934).1332011 Metabolismamong them all had some difficulties with Adolf Hitler, or he with them.15Most of them emigrated, and life was not made easy for those who stayed.What is Life?Another emigrant was the eminent quantum-physicist Erwin Schrödinger(1887–1961) who found a fairly comfortable temporary home at the Schoolof Advanced Studies in Dublin, Ireland.

There, in 1943, he gave a course ofpublic lectures entitled ‘‘What is life?” which was afterwards published as abooklet.16To the modern reader – well-informed by newspapers about DNA andthe human genome – the book is somewhat obsolete, but it is stillworshipped by theoretical physicists. Schrödinger expounds the idea thatthe gene must be a molecule lest it be subject to constant change by thethermal motion. He observes that a gene seems to be stable over manygenerations as put in evidence by the persistence of the well-documentedHabsburg lower lip, a slight deformity of the lip in the members of thatillustrious and oft-portrayed family. Also, in order to account for mutations,Schrödinger emphasizes the need for meta-stable states in the gene, i.e.energetic minima separated from other, conceivably lower minima bybarriers.

He sees thermal motion, or possibly X-rays, or cosmic rays as theonly means to overcome such barriers. This seems to offer a satisfactoryexplanation for the fact that a mutation is a rare event because, after all, weare not very often exposed to X-rays, and the temperature must not beincreased much beyond 37°C.The closest Schrödinger comes to answer his self-imposed questionabout life is, when he says 17What is the characteristic feature of life? When is a piece of matter said tobe alive? When it goes on ‘‘doing something”, moving, exchangingmaterial with its environment, and so forth, and that for a much longerperiod than we would expect an inanimate piece of matter to ‘‘keep going”under similar circumstances.15In the 1930’s German scientists were not allowed to accept the Nobel prize, because Hitlerwas angered when the 1935-peace prize was given to Carl von Ossietzky (1889–1938), awell-known pacifist who, at the time of the award, was kept in a concentration campwhere he later died.16 E.

Schrödinger: ‘‘What is life? The physical aspect of the living cell.” Cambridge: At theUniversity Press. New York: Macmillan Company (1945).17 E. Schrödinger: ‘‘What is life? …” loc.cit. p. 70.What is Life?321In 1918, after World War I, Schrödingermade up his mind to abandon physics forphilosophy, but the city where he hadhoped to obtain a university post was lostto Austria in the peace treaties. ThereforeSchrödinger remained a physicist.18Fig. 11.3. Erwin Schrödinger (1887–1961)Well, that answer seems to be begging the question. Maybe we cannothave a better – and shorter – answer than that.

But I, for one, wouldcertainly wish to. Since we are on the subject, let me also quote Asimov,19himself a biochemistA living organism is characterized by the ability to effect a temporary andlocal decrease in entropy by means of enzyme-catalysed chemicalreactions.So, thus we are back on the subject of entropy.

Schrödinger devotes thelast part of his booklet to it. He says that a living organism feeds onnegative entropy, meaning that an animal maintains a high level of orderbecause it feeds on plants which have themselves a high degree oforderliness, i.e. a low entropy. He says:Indeed, in the case of higher animals we know the kind of orderliness theyfeed upon well enough, viz. the extremely well-ordered state of matter inmore or less complicated organic compounds, which serve them asfoodstuffs.I do wonder though whether that argument is not a trifle superficial.

Afterall, we have seen that, before the animal does anything constructive with thefoodstuffs, it breaks them down to material of lesser order in the digestiveprocess. So, at least we can say that the organism does not make the most ofthe order that is offered to it.1819I. Asimov: ‘‘Biographies …” loc.cit. p. 621.I. Asimov: ‘‘Life and Energy.” Avon Publishers of Bard, New York (1972).I owe much of the information presented in this chapter to the study of that book byAsimov.

On these pages I have often quoted Asimovs book of biographies andoccasionally other science essays by the author. Indeed, if the truth were known, I doadmire Asimov’s way of writing, – except when he writes Science Fiction.32211 MetabolismHowever, the metaphor feeding on negative entropy – the term wasquickly changed into negentropy – has fired the imagination of physicists ofthe more esoteric type and theologians. I am told that Teilhard de Chardin, aJesuit palaeontologist and anthropologist – who attempted to reconcile thetheory of evolution with the teachings of the catholic church – was inspiredby negentropy. Schrödinger cannot be blamed, perhaps. After all he wasgiving a public lecture to a mixed audience. And he lived to regret hissimplified presentation. Indeed, in the German translation of his book in1951 he says 20My remarks about negative entropy have been criticized by experts inphysics.

I have to say to them that I should have used the word freeenergy, if I had spoken to them.Let us look at plants next, surely one of the sources of negentropy foranimals. This is an interesting subject in itself. What happens in a plant isthe photosynthesis of glucose from the CO2 of the air and from H2O of thesoil and the release of oxygen. We rewrite the stoichiometric formula frombefore, except in reverse order as is appropriate for the synthesis of glucoserather than its decomposition.6CO2 6 H 2O  C6 H12O6 6O2kJ∆hR 2798 mol.J∆ sR 241 molKIn some way this is the worst possible case for a chemical reaction: Theenergy – or enthalpy – increases and the entropy decreases.