Good Science Writers: Albert Lehninger

 
Albert Lehninger (1917 - 1986) was a biochemist whose main research interest was the production of energy by mitochondria. His second book, Bioenergetics was published by W.A. Benjamin Inc. in 1965 as part of a series of biochemistry books by well-known scientists. One of the other books in the series was Molecular Biology of the Gene by James D. Watson. Neil Paterson of W.A. Benjamin was the man behind getting these scientists to write books for the general public and students.

Later, when Neil Patterson had moved to Worth Publishers, he persuaded Lehninger to write a textbook and the first edition of Biochemistry was published by Worth in 1970. Following Lehninger's death in 1986, the book, now called Lehninger Principles of Biochemistry was taken over by David Nelson and Michael Cox and the current publisher is W.H. Freeman and Company.

Lehninger's writing was characterized by an emphasis on basic chemical principles and his style was crisp and unapologetic. He is not mentioned by Richard Dawkins in his book: The Oxford Book of Modern Science Writing but that's no surprise because many well-known textbook authors are not recognized as good science writers.

The first excerpt comes from Bioenergetics )pp. 18-20).

The First Law [of thermodynamics] tells us that energy is conserved; every physical or chemical change must satisfy this principle. However, there is another fundamental aspect of energy exchange which is not explained by the First Law. A simple example will serve to illustrate the problem.

Suppose we place two blocks of copper together, one hot and one cold, and seal them in an insulated container. The temperature of the hot block will fall and that of the cold block will rise until they both reach some intermediate temperature, which at equilibrium will be uniform throughout both blocks. The flow of heat and thus of energy from the hot block to the cold is spontaneous. However, if we put two identical blocks of copper, both at the same temperature, into such a container, we know that they will remain at the same temperature; we would never expect the temperature of one block to rise spontaneously and that of the other to fall. However, if this should happen, it would not violate the First Law because the energy lost by one block would be gained by the other; the total energy of the two blocks would remain the same.

It is quite clear from considering this example ... that spontaneous physical or chemical changes have a direction which cannot be explained by the First Law. In brief, all systems tend to approach equilibrium states in which temperature, pressure, and all other measurable parameters of state become uniform throughout. Once they reach such an equilibrium they no longer change back spontaneously to the nonuniform or nonrandom state. When the two blocks of copper in our model have reached exactly the same temperature, all the heat energy originally contained in the two blocks has been maximally randomized, and we know that it will never by itself "unrandomize." The Second Law of thermodynamics provides us with a new yardstick or criterion for predicting the tendency of a physical process to occur and the direction in which it will occur. First, it defines entropy as a randomized state of energy that is unavailable to do work. Second, it states that all physical and chemical processes proceed in such a way that the entropy of the system becomes the maximum possible. At this point there is equilibrium.

The second excerpt is from the first edition of Biochemistry (1970) pp. 276-278. (The second edition is shown in the figure.)

Complex organic molecules such as glucose, contain much potential energy because of their high degree of structural order; they have relatively little randomness, or entropy. When the glucose molecule is oxidized by molecular oxygen to form six molecules of CO₂ and six of water, its atoms undergo an increase in randomness; they become separated from each other and may assume different locations in relation to each other. As a result of this transformation, the glucose molecule undergoes a loss of free energy, which is useful energy capable of doing work at constant temperature and pressure.

The free energy of glucose so released is harnessed by the cell to do work. Biological oxidations are in essence flameless or low-temperature combustions. As we have seen, heat cannot be used as energy source by living organisms, which are essentially isothermal, since heat can do work at constant pressure only when it can flow from a warmer to a cooler body. Instead, the free energy of cellular fuels is conserved as chemical energy, specifically the phosphate-bond energy of adenosine triphosphate (ATP). ATP is enzymatically generated from adenosine diphosphate (ADP) and inorganic phosphate in enzymatic phosphate-group transfer reactions that are coupled to specific oxidation steps during catabolism. Since the ATP so formed can now diffuse to those sites in the cell where its energy is required, it is thus also a transport form of energy. The chemical energy of ATP is then released during transfer of its terminal phosphate group(s) to certain specific acceptor molecules, which become energized and can do work.

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[Photo Credit: Mitochondria and Neuroprotection—In Memory of Albert L. Lehninger]