Basic Themes

Sign in at www.thomsonedu.com/login to test yourself on these concepts. 

Disciplines that appear to be unrelated to biochemistry can provide answers to important biochemical questions. For example, the MRl (magnetic resonance imaging) tests that play an important role in the health sciences originated with physicists, became a vital tool for chemists, and currently play a large role in biochemical research. The field of biochemistry draws on many disciplines, and its multidisciplinary nature allows it to use results from many sciences to answer questions about the molecular nature of life processes. Important applications of this kind of knowledge are made in medically related fields an understanding of health and disease at the molecular level leads to more effective treatment of illnesses of many kinds. 

The activities within a cell are similar to the transportation system of a city. The cars, buses, and taxis correspond to the molecules involved in reactions (or series of reactions) within a cell. The routes traveled by vehicles likewise can be compared to the reactions that occur in the life of the cell. Note particularly that many vehicles travel more than one route—for instance, cars and taxis can go almost anywhere—whereas other, more specialized modes of transportation, such as subways and streetcars, are confined to single paths. Similarly, some molecules play multiple roles, whereas others take part only in specific series of reactions. Also, the routes operate simultaneously, and we shall see that this is true of the many reactions within a cell. 

To continue the comparison, the transportation system of a large city has more kinds of transportation than does a smaller one. Whereas a small city may have only cars, buses, and taxis, a large city may have all of these plus others, such as streetcars or subways. Analogously, some reactions are found in all cells, and others are found only in specific kinds of cells. Also, more structural features are found in the larger, more complex cells of larger organisms than in the simpler cells of organisms such as bacteria. 

An inevitable consequence of this complexity is the lai e quantity of terminology that is needed to describe it learning considerable new vocabulary is an essential part of the study of biochemistry. You will also see many cross-references in this book, which reflect the many connections among the processes that take place in the cell. 

---

A basic theme throughout this book is that the long-chain character of polymers is what makes them different from their low molecular weight counterparts. Although this notion was implied in several aspects of the discussion of the shear dependence of viscosity, it never emerged explicitly as a variable to be investi-tated. It makes sense to us intuitively that longer chains should experience higher resistance to flow. Our next task is to examine this expectation quantitatively, first from an empirical viewpoint and then in terms of a model for molecular motion. 

The precise sequence of events resulting from the infection of a cell by a virus will vaiy with different virus-host systems, but they will be variations of four basic themes. 

After our formulation of the hypothesis in 1975, many pieces of evidence have come to support the basic theme. A positive association of dysplasia, representing advanced stages of the process, with nitrite levels in the gastric juice has been reported in England and Colombia (, . Higher than expected... 

The vertebrates show many morpho-functional variants on a basic theme (Chap. 2). Some of these, such as the pattern of distribution of the genetically distinct chemosensory neurones within die VN epithelium, will be related to the level of complexity of the animal. In some groups, the VNO can be equally complex, whilst the accessory areas of the brain will differ in complexity, as in the advanced reptiles and mammals. Eventually, detailed comparisons of the genomic repertoire of the various accessory systems should reveal the extent of the operational distinctions amongst them. Of particular interest would be the events which account for the suppression of AOS morphogenesis, and those which compensate for its absence. 

The net quenching reaction in eq. 2, which leads to separated redox products capable of oxidizing and reducing water, relies on a series of electron transfer steps. The basic theme of this account is excited state and related electron transfer events which occur in such systems and the basis that we have for understanding them both experimentally and theoretically. 

By way of brief background, I would like to summarize how CMA has organized itself to deal with TSCA, and describe some of the basic themes which we have followed for virtually all of the issues raised by the Act. 

The basic purpose of HMTA is to ensure safe transportation of hazardous materials through the nation s highways, railways, and waterways. The basic theme of HMTA is to prevent any person from offering or accepting a hazardous material for transportation anywhere within this nation if that material is not properly classified, described, packaged, marked, labeled, and properly authorized for shipment pursuant to the regulatory requirements. 

Due to its nature, this review is solely devoted to authors achievements, rather than the procedural details or review of other contributions. Consequently, the discussions and the references are strongly biased towards authors work. Also, due to space limitations it is not possible to discuss all of the problems considered in the work the discussions are limited to three problems which constitute the basic theme of authors activities ... 

Bravo and coworkers explored the chemistry of an enantiomerically pure p-toluenesulfinyl trifluoroacetone (indeed other perhaloalkyl groups were also explored) (Eq. 88) [262, 263]. Treatment with diazomethane led to the stereoselective formation of epoxides, potentially useful C-4 building blocks with a high level of functionality [264] there are many published variations on this basic theme. 

A variation on the basic theme of receptor Tyr kinases is seen in receptors that have no intrinsic protein kinase activity but, when occupied by their ligand, bind a soluble Tyr kinase. One example is the system that regulates the formation of erythrocytes in mammals. The cytokine (developmental signal) for this system is erythropoietin (EPO), a 165 amino acid protein produced in the kidneys. When EPO binds to its plasma membrane receptor (Fig. 12-9), the receptor dimerizes and can now bind the soluble protein kinase JAK (Janus kinase). This binding activates JAK, which phosphory-lates several Tyr residues in the cytoplasmic domain of the EPO receptor. A family of transcription factors, collectively called STATs (signal transducers and activators of transcription), are also targets of the JAK kinase activity. An SH2 domain in STATS binds (P)-Tyr residues in the EPO receptor, positioning it for this phosphorylation by JAK. When STATS is phosphorylated in re-... 

It is possible that quite different molecular architectures may occur in membranes from different sources. Current research may result in a much more dramatic revision or complete rejection of the bilayer model for some membranes, especially in such systems as mitochondria (30) and chloroplasts (2). However, it is also possible that structural differences are only variations on the basic theme of the bilayer, from myelin at one extreme to mitochondria or chloroplasts on the other. One must not readily reject the fundamentals of the Danielli concept, especially in view of the present inadequate knowledge of the properties of phospholipids in water. Clearly the molecular architecture of membranes is speculative, but most aspects of the problem are amenable to direct experimental test by the new physical techniques. A consistent model for biological membranes will emerge quickly. 

Variations on this basic theme have been reported to reach more or less complex Type I branched-chain sugars (Scheme 2). A particular emphasis has been given on the use of... 

Strictly speaking, there are only two ways in which gases can be in a sample. If gas atoms are mixed with host atoms on a microscopic scale, the gas is dissolved if gas atoms are on the surfaces that bound the sample, the gas is adsorbed. There are quite a few complications and variations on these basic themes, however, as will be discussed. From a macroscopic viewpoint, and from the viewpoint of laboratory practice, it is sometimes difficult to distinguish between solution and adsorption,... 

Most methods for DNA hybridization require substantial amounts of DNA, and it is not uncommon to process 5-50 g (wet weight) of cells. Although numerous methods have been developed for isolation of DNA from microorganisms, many are modifications on basic themes, and the following account is intended to be an overview of the procedures. Cells are generally grown to log phase to ensure that each has undergone complete... 

By now we have set up the basic machinery which permits the principles of irreversible thermodynamics to be applied to problems of interest. We next illustrate the method of procedure by an elementary example. The same approach will be used in later sections, with appropriate variations on the basic theme. 

The basic themes of metal-metal bonded dimers were established years ago and have remained largely unchanged. However, new aspects of metal-metal bonding have been discovered and in addition, apphcation of metal metal bonded complexes in other areas has grown. Important contributions in emerging fields such as nanomaterials, fuUerene see Carbon Fullerenes) chemistry, combinatorial catalytic research, molecular recognition, and dendrimers have all utihzed metal metal bonded complexes. 

Reactions are difficult to learn when each reaction is considered a unique and isolated event. Avoid this tendency. Virtually all chemical reactions are woven together by a few basic themes. After we learn the general principles, specific reactions then fit neatly into a general pattern. 

Content Organic Chemistry accents basic themes in an effort to keep memorization at a minimum. Relevant materials from everyday life are used to illustrate concepts, and this material is integrated throughout the chapter rather than confined to a boxed reading. Each topic is broken down into small chunks of information that are more manageable and easily learned. Sample problems are used as a tool to illustrate stepwise problem solving. Exceptions to the rule and older, less useful reactions are omitted to focus attention on the basic themes. 

By introducing one new concept at a time, keeping the basic themes in focus, and breaking complex problems down into small pieces, I have found that many students find organic chemistry an intense but leamable subject. Many, in fact, end the year-long course surprised that they have actually enjoyed their organic chemistry experience. 

---