Proteins translational movements

The diffusion of proteins and peptides in solution is dictated by the same considerations as those discussed in section 3.6. The rate of translational movement depends on the size of the molecule, its shape and interactions with solvent molecules. The rate of translational movement is often expressed by a frictional coefficient, f, defined in relation to the diffusion coefficient D, by equation (11.4) ... 

The diffusion coefficients and translational movements of proteins are important in considering the release of proteins from hydrogel matrix devices and other delivery vehicles, and in membrane transport, as far as this can be considered to be a passive diffusion process. Changes in shape during membrane transport in a lipid environment may also have to be considered. Table 11.6 gives some values of diffusion coefficient of a number of therapeutic peptides and proteins. 

Figure 10 Illustration of translational movements produced by directional growth of F-actin a simplified model, actually many kinds of proteins are involved to generate fast translation.

In cooperation with many kinds of actin-binding proteins, the G-F transformation of actin generates translational movement of a bacterial cell in a host cell, as in Figure 10 [46], Anchoring and nucleation proteins, depolymerizing proteins, and cross-linking proteins work to make possible a fast cycle of actin molecules from one end of F-actin to the other end, that is, tread-milling. This system has been artificially reconstructed in vitro [47]. 

Pig. I. Mechanism of action of antisense oligonucleotides. After binding to the complimentary mRNA sequence f/), the oligonucleotides inhibit protein translation by interference with movement of the mRNA through the translation machinery (2), or by inducing RNAse H-dependent degradation of the mRNA in the duplex (3). 

By a combination of enzyme digestion, chemical or antibody labelling or physical techniques such as NMR, it has been shown that all membranes thus examined are clearly asymmetric with regard to their lipids as well as their proteins. This asymmetry is maintained because, although lipids show rapid rotational and translational movement, they only move from one leaflet to the other at very slow speeds. 

The discovery of Green Fluorescent Protein (GFP) and the development of technology that allows specific proteins to be tagged with GFP has fundamentally altered the types of question that can be asked using cell biological methods. It is now possible not only to study where a protein is within a cell, but also feasible to study the precise dynamics of protein movement within living cells. We have exploited these technical developments and applied them to the study of translation initiation factors in yeast, focusing particularly on the... 

The macroscopic rates measured by radiolabel experiments should not be taken to reflect maximum rates of the motors involved. As with mitochondrial transport, the net rate of slow component proteins reflects both the rate of actual movement and the fraction of a time interval that a structure is moving. The elongate shape of cytoskeletal structures and their potential for many interactions means that net displacements are discontinuous. If a structure is moving at a speed of 2 j,m/s, but on average only moves at that rate for one second out of every 100 seconds, then the average rate for the structure will translate to a net rate of only 0.02 pm/s [31]. 

Mineralocorticoids are believed to increase sodium reabsorption by affecting sodium channels and sodium pumps on the epithelial cells lining the renal tubules.18,58 Mineralocorticoids ability to increase the expression of sodium channels is illustrated in Figure 29-5. These hormones enter the tubular epithelial cell, bind to receptors in the cell, and create an activated hormone-receptor complex.18 This complex then travels to the nucleus to initiate transcription of messenger RNA units, which are translated into specific membrane-related proteins.27,58 These proteins in some way either create or help open sodium pores on the cell membrane, thus allowing sodium to leave the tubule and enter the epithelial cell by passive diffusion.27,83 Sodium is then actively transported out of the cell and reabsorbed into the bloodstream. Water reabsorption is increased as water follows the sodium movement back into the bloodstream. As sodium is reabsorbed, potassium is secreted by a sodium-potassium exchange, thus increasing potassium excretion (see Fig. 29-5). 

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