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This article reports the results of a recent study to evaluate the usefulness of physical models of molecular structures as a new tool with which to teach concepts of molecular structure and function. Of seven different learning tools used by students in this introductory biochemistry class, the use of the physical models in a laboratory was rated as most useful. These results suggest that physical models can play an important role in capturing the interest of students in the subject of molecular structure and function. These physical models often stimulate more sophisticated questions in the minds of students, which can then be more appropriately explored using computer visualization tools.

The technology now exists to construct physical models of proteins based on atomic coordinates of solved structures. We review here our recent experiences in using physical models to teach concepts of protein structure and function at both the high school and the undergraduate levels. At the high school level, physical models are used in a professional development program targeted to biology and chemistry teachers. This program has recently been expanded to include two student enrichment programs in which high school students participate in physical protein modeling activities. At the undergraduate level, we are currently exploring the usefulness of physical models in communicating concepts of protein structure and function that have been traditionally difficult to teach. We discuss our recent experience with two such examples: the close-packed nature of an enzyme active site and the pH-induced conformational change of the influenza hemagglutinin protein during virus infection.A common goal of biochemistry educators is to provide students with a deep understanding of fundamental concepts underlying protein structure and function. This is most commonly done by exposing students to stunning two-dimensional color graphics of proteins in textbooks and frequently augmenting these static figures with interactive images that can be rotated in three-dimensional space in a computer environment. Although this approach is successful for those students who are able to infer three-dimensional information from these inherently twodimensional representations, many other students fail to make this inference. For them, the molecular world of proteins remains an abstraction for which they have little interest. We have found that physical models of proteins ( Fig. 1) are amazingly effective tools that initially capture the interest of this larger group of students and motivate them to learn more about this invisible, molecular world. These physical models are synergistic with computer visualization tools, allowing students to generalize their initial understanding of a specific protein to other structures that are explored in a computer environment. We review here our recent experience with the use of physical models to make this molecular world "real" for students at both the high school and the undergraduate levels. A THEORETICAL BASIS FOR THE VALUE OF PHYSICAL MODELS IN TEACHING ABSTRACT CONCEPTS IN SCIENCEThe value of physical models of small molecules in organic chemistry courses is well known to biochemistry educators. However, these small molecule kits are not practical for modeling the higher order molecular structures of proteins. Experienced researchers have learned to infer three-dimensional information from two-dimensional images of proteins or to manipulate interactive, computergenerated images of proteins. Unfortunately, our current educational practice treats inexpert students as though they were expert researchers. Students are introduced to proteins through two-dimensional drawings or interactive computer visualiz...

Abstract— Pyrimidine (Pyr) adducts constitute a significant fraction of the photoproducts formed in DNA exposed to far UV light. The primary and secondary DNA structure affects the rate of Pyr adduct formation; for example, it increases with decreasing (Ade + Thy)/(Gua + Cyt) of the DNA and with increasing dehydration, and it is greater in double‐stranded than in single‐stranded DNA. Pyrimidine adducts do not appear to be involved in inter‐strand cross‐links, and 313 nm‐induced photolysis of Pyr adducts does not cause strand breakage. The action spectrum for Pyr adduct formation is qualitatively similar to that for Pyr < > Pyr formation; the calculated quantum yields for its formation is essentially wavelength independent over the range 254 nm to 280 nm, but decreased somewhat at shorter wavelengths (240 nm). The biological role of Pyr adducts is still not clear. The data suggest that either Pyr adducts and their photolysis products are not lethal, or that both are lethal but can be repaired under certain conditions.

Abstract— In an ethanolic solution native T7 DNA can undergo conformational transitions from the B conformation (0% ethanol) to the C‐like (60% w/w ethanol) and the A (80% w/w ethanol) conformations. We have investigated the formation of three classes of thymine‐derived photoproducts in T7 DNA irradiated (280 nm) in the B, C‐like, and A conformations, which were monitored by circular dichroism measurements. We find that the predominant class of thymine‐derived photoproducts in any conformational state is cyclobutyl dipyrimidines. While the ‘spore product,’ 5‐thyminyl‐5,6‐dihydrothymine, which belongs to another class of photoproductsf does form in native DNA in the A conformation, its yield in denatured DNA at 80% ethanol is the same as that in native DNA. The yield of pyrimidine adduct, a third photoproduct class, is a maximum at 50–60% ethanol. This effect of ethanol is probably not due to the ethanol‐induced C‐like conformation, however, since pyrimidine adduct formation is not enhanced when T7 DNA is irradiated in the C conformation in 6 M CsCl or in intact phage. We conclude from these and other data in the literature that the degree of hydration rather than the conformational state is the critical factor in determining which of the photoproducts will form in native DNA.