Common component hypothesis

When labeled polypeptides traveling down the axon are analyzed by SDS polyacrylamide gel electrophoresis, materials traveling in the axon can be grouped into five distinct rate components [6], Each rate component is characterized by a unique set of polypeptides moving coherently down the axon (Fig. 28-3). As specific polypeptides associated with each rate class were identified, most were seen to move only within a single rate component. Moreover, proteins that have common functions or interact with each other tend to be moved together. These observations led to a new view of axonal transport, the structural hypothesis [7]. This model can be stated simply proteins and other molecules move down the axon as component parts of discrete subcellular structures rather than as individual molecules (Table 28-1). 

No information was located regarding the mechanism by which tetryl enters the blood stream from the lungs, skin, or gastrointestinal tract, the mechanism by which tetryl is transported in the blood stream, or the mechanism of toxicity for tetryl. Earlier studies suggested that the cause of tetryl-induced dermatitis, which is the most common and widely studied adverse effect, may be both physical (direct irritation by sharp tetryl crystals) and chemical (by reacting with components of the skin) (Ruxton 1917). The chemical hypothesis was later advanced by others as well (Bain and Thompson 1954 Brownlie and Cumming 1946). Bain and Thompson (1954) specifically suggested that histamine release may result from a tetryl-induced sensitization reaction or from direct tetryl-induced release from mast cells. 

In this book all research questions are addressed and then answered via the construction of two research hypotheses, commonly called the null hypothesis and the alternate hypothesis. (Although another name for the alternate hypothesis, the research hypothesis, has its own appeal, we employ the commonly used term "alternate hypothesis" in this book.) Both of these hypotheses are key components of the procedure of hypothesis testing. This procedure is a statistical way of doing business. It is described and discussed in detail in Chapter 6, but it is beneficial to introduce the main concept here. 

A probability value can be represented as a fraction or as a decimal value. In addition, it is common in some aspects of Statistics to multiply the decimal expression of a particular probability by 100 to create a percentage statement of likelihood. A probability of 0.5 would thus be expressed as a 50% chance that an event would occur. Percentage statements of likelihood are a central component of hypothesis testing, which is introduced later in the chapter. 

The chemical composition of DNA was determined largely by Albrecht Kos-sel between 1882 and 1897 and P. A. Levene in the 1920s as suitable analytical techniques were developed. Unfortunately, Levene mistakenly believed that DNA was a small and relatively simple molecule. His concept, referred to as the tetranu-cleotide hypothesis, significantly retarded further investigations of DNA. Instead, proteins (the other major component of nuclei) were viewed as the probable carrier of genetic information. (By the end of the nineteenth century it was commonly accepted that the nucleus contains the genetic information.)... 

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