Cellular machinery

Alpha helices are sufficiently versatile to produce many very different classes of structures. In membrane-bound proteins, the regions inside the membranes are frequently a helices whose surfaces are covered by hydrophobic side chains suitable for the hydrophobic environment inside the membranes. Membrane-bound proteins are described in Chapter 12. Alpha helices are also frequently used to produce structural and motile proteins with various different properties and functions. These can be typical fibrous proteins such as keratin, which is present in skin, hair, and feathers, or parts of the cellular machinery such as fibrinogen or the muscle proteins myosin and dystrophin. These a-helical proteins will be discussed in Chapter 14. 

Proteins are usually separated into two distinct functional classes passive structural materials, which are built up from long fibers, and active components of cellular machinery in which the protein chains are arranged in small compact domains, as we have discussed in earlier chapters. In spite of their differences in structure and function, both these classes of proteins contain a helices and/or p sheets separated by regions of irregular structure. In most cases the fibrous proteins contain specific repetitive amino acid sequences that are necessary for their specific three-dimensional structure. 

As a perspective to this review, we conclude with recent developments in the use of whole cells to control the growth of nanopartides. Such approaches should allow one to take advantage of the whole cellular machinery and, combined with genetic engineering, appear very promising for the development of a green nanochemistry. 

Replacement of the famesyl group by lipid analogues could be performed for full length Ras proteins in vitro by means of the enzyme famesyltrans-ferase. When such partially modified Ras constructs were applied in Xenopus oocytes the cellular machinery completed modification (endoprotease activity, carboxymethylation and palmitoylation). In these cases the H-Ras famesyl group could be stripped off most of its isoprenoid features that distinguish it from a fatty add without any apparent effect on its ability to induce oocyte maturation and activation of mitogen-activated protdn kinase In contrast, replacement by the less hydrophobic isoprenoid geranyl causes severely delayed oocyte activation. 

The Protos warfare on their Lept neighbors depended heavily on chemicals, but ants are by no means unique in making extensive use of chemicals for communication and warfare. From one-celled organisms to complex plants and animals, many living creatures do the same. As species develop over evolutionary time, it is relatively easy for them to adapt their cellular machinery to producing chemicals for communication, warfare, and other purposes. These chemicals facilitate the way of life of organisms spread all across the biological spectrum. 

The body s natural defenses against overenthusiastic oxidation include a-lipoic acid, reduced glutathione, ascorbic acid, the tocopherols, the carotenoids, and a number of enzymes such as epoxide hydrolase and the like. Very efficient DNA repair systems also operate defensively. These various means are remarkably effective, but DNA assault is continuous, cumulative, and implacable. Thus, many degenerative diseases are associated with aging because of the gradual slippage in functional fidelity of cellular machinery which occurs with age. 

The review of literature in this chapter is far from complete, and for the sake of brevity we have had to largely exclude an extensive body of work based entirely on cultured cell lines. However, such studies are vital if we are to develop mechanistic models of how the annexins contribute to the pathology of the diseases with which they are increasingly becoming associated. Annexins are evolutionarily conserved proteins and appear for the most part to be cellular Ca2+ effectors structural and regulatory components of the cellular machinery that physically build connections between membranes and cytoskeleton and regulate and nucleate signalling complexes at these interfaces. 

The ligand causes a stimulus by binding a receptor. That stimulus is then transformed by the cellular machinery into a response. Stephenson described the mathematical relationship between the stimulus and response as the transducer function (Equation 5.15). The response is some function, most likely nonlinear, of the stimulus. 

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