A Freshman Biochemistry Course Francis J. De Toma and Mary K. Campbell Mount Holyoke College, South Hadley, MA 01075
During the years 1977 through 1979, a one-semester freshman hiochemistry course was offered at Mount Holyoke. I t was possible to develop this course and to offer it on an experimental basis because of grant funding. The existence of the course has had a permanent and desirable impact on the curriculum. Freshman biochemistry served as an alternative to the traditional freshman chemistrv course. also one semester in length a t Mount Holyoke. ]nuaddition to providing another point of entry for the hiochemistry or chemistry major, Freshman Biochemistry was taken by about 20 percent of the students involved to fulfill the college " science distribution requirement. As a result of this course, some sections of our eeneral chemistrv course have been modified to include " more hiochemical examples than was previously the case. This point will he discussed below in greater detail. The unifying theme for the course was the origin and early stages of the evolution of life on earth. Thus, the fundamentals of introductory chemistry-i.e., atomic and molecular structure, acidity and basicity, thermodynamics, reaction kinetics, oxidation-reduction reactions and the like-were presented in a context that was of considerable interest to the students. The first group of lectures, for example, dealt with the "big hang" theory, the synthesis of elements in stellar interiors, and with the radiochemical evidence for the age of the earth and the solar system. In this manner, the student4 were introduced to nuclear chemistry and were given practice in balancing equations. After a hrief description of the hypothesis of Oparin and of Haldane that molecular components of cells arose ahiotically on the ~rimitiveearth. the theorv of the chemical bond was treated in a manner designed to support the hypothesis and thus to advance the aims of the course. The structures of water, ammonia, and methane were treated in the context of the fact that several amino acids can he synthesized ahioticallv in the lahoratory from these compounds. Formaldehyde was chosen as an example of bonding involving sp2 hyhrid orbitals and hydrogen cyanide as an example for sp hybridization. I t was pointed out that the existence of these molecules in interstellar space has been estahlished spectroscopically ( I ) , and that they are the starting materials for the lahoratory syntheses of ribose (2) and adenine (31,respectively, under ahiotic conditions. Other topics were developed in a similar way. Hydrogen honding was discussed in the context of protein and nucleic acid structure, and the topic of acidity and hasicity was discussed in the context of the major physiological buffer systems, both intracellular and extracellular. Likewise, oxidation-reduction reactions were discussed in the context of the ~~~
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electron transport-oxidative phosphorylation system of aerobic organisms, and the interaction of matter and light was 1 m . r u t t ~ l 11, terms t i IIU. ~ m m : , nI t k h t t r l l > p i t ~ g S>-II-I~. I ~ , h o l ~ r c \ . n l l l t , t ~I,. ~ 'l'lw tllvt.~lll dw-in>i,> %I, phclqlhl~lil)~~l I I I I ~ s-~e lIi . ~ ; + m o l \ . n n d t h t kirn.tl8. < r,:~,.ii~~l,. ~ i III 111 1111 catalyzed and enzyme catalyzed, were also treated at some length. Topics of a more biological nature included a treatment of the fossil cell record and of hiochemical evolution, using the cytochromes as an example. Tahle 1shows a list of the topics covered in the course. The lectures and lahoratory instruction for the course were shared by amemher of the biology department and amember of the chemistry department. Two types of source material were used for the lecture portion of the course, one the textbook for the general chemistry course, and the other a selection of offprints from Scientific American, listed in Tahle 2. These offprints dealt with the age of the earth, the ahiotic synthesis of macromolecules, fossil cells, and biochemical evolution. The size of the course was limited to twenty-four oarticioants each time it was offered. which is the caoacitv . .of one lahoratory section. Each laboratory exercise was outlined in detail in a mimeographed description several pages long. Some experiments were of aproject type and required several weeks. Each experiment was discussed briefly in a short explanatory session at the start of each lahoratory period. For the first lahoratorv exercise, the Miller-Urev exueriment-in which an electric discharge is passed throuih a mixture of HZ,CH4, NH3, and Hz0 for a period of a weekwas duplicated (4). In the suhseqnent laboratory period, the resulting "primordial soup" was subjected to paper chromatography along with a number of known amino acids. Several amino acids-including glycine, aspartic acid, and P-alanine-were identified as products of the Miller-Urey reaction with varying degrees of confidence, depending principally on Table 1. Lecture Topics Origins of the elements. Age of the solar system. The formation and age of the earth. 2. The formation of the earth's atmospheres. 3. Atomic structure. 4. Molecular orbitals. Chemical bonding. 5. The abiotic generation of life. The Miiier-Urey experiment. The Periodic
1.
6. 7. 8. 9. 10. 11.
Table. Proleinoids and microsphere. Water, acids, and bases. Hydrogen bonding. Buffers. Elementary thermodynamics. Elementary kinetics. Fossil cells. Evolution of cell metabolism.
Volume 59
Number 3
March 1982
227
Table 2.
Table 3.
List of Source Materials
Laboratory Projects
The theory and use oi paper chromatography The Miller-Urey experiment: the formation of amino acids in a reducing atmosphere. 3. Spectraphotometry. 4. Preparation of proteinoids. 5 . The enzymatic activity of proteinoids. Preparation of microspheres. 6. pH and buffers. 7. Determination of the apparent equilibrium constant for a chemical reaction. 8. Cell structure. Mitosis and Meiosis. 9. Reaction kinetics. 10. Oxidation. reduction. and the electron transoorl chain. 1. 2.
3. 4. 5.
6.
7.
(1970). Offprint # I 1 8 8 "The Oriqin of the Earth" by Harold C Urey, Scr. Amer, 187[4], 53-60 (1952). Offprint #833. "The Origin d Life" by George Waid, Sci. Arne,., 191[2]. 44-53 (1954). Offprint #47. "The Oldest Fossils" by Elso S,Borghoorn. Sci. Amer. 224[5], 30-42 (1971). "The Evolution of the Earliest Cells" by J. William Schopf, S c i Amer. 239[3], 110-138(1978). "Chemical Evolution and the Origin of Life" by Richard E. Dickerson. Sci. Amer.. 239[3]. 70-86 (1978).
Gmnerd Reference ~-
"Life: Origin and Evolution-a collection of readings from Scientific American," W. H. Freeman and Company, San Francisco, 1979. A Four-pat F m Loop Series from Harper and Row Publishers The Origin of Life: Part 1 Formation of Amino Acids Part 2 Preparation and Properties of Proteinaids Part 3 Preparation of Proteinoid Microspheres Part 4 Properties of Proteinoid Microspheres
the skill of the students in applying sample and standards to the chromatoeram. Another labhratory exercise was based on the work done by Fox and his rroun. on the abiotic synthesis of proteinoids (protein-like polymers) from amino acid mixt&es. These thermal condensation polymers were presumably produced on the early earth when amino acids which were dissolved in ocean water splashed onto hot volcanic rocks. The condensation must have taken place under dry conditions, presumably after evaporation of the ocean water from the hot rocks of Fox's hypothesis, leaving behind the amino acids. In the laboratory, suitable conditions were obtained by using a several weeks for the synthesis, purification, and characterization of the proteinoids. During the first lahoratorv . .neriod. an amino acid mixture was added to a melt of aspartic and glutamic acids kept in a n oil bath at 180°C. The mixture was maintained under nitrogen at this temperature for three hours. In a subsequent lahoratory period, a simple purification was carried out by washing the produd with ethanol, followed by dialysis against distilled water. Next, the proteinoids were characterized with respect to two properties, their catalytic activity (61, and their tendencv to form microsnheres 17). The esterase activity of the n
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