R-groups hydrophilic

A tertiary structure is stabilized by interactions that push amino acids with hydrophobic R groups to the center and pull amino acids with hydrophilic R groups to the surface, and by interactions between amino acids with R groups that form hydrogen bonds, disulfide bonds, and salt bridges. 

Elbert R, Laschewsky A and Ringsdorf H 1985 Hydrophilic spacer groups in polymerizable lipids— formation of biomembrane models from bulk polymerized lipids J. Am. Ohem. Soc. 107 4134-41... 

Fig. 3-10 The 20 protein amino acids divided by R group character as (a) hydrophobic, (b) hydrophilic, and (c) mixed. (Reprinted with permission from W. K. Purves and G. H. Orians, Life The Science of Biology," pp. 63-81, Copyright 1987 by Sinauer Associates, Inc., Sunderland, MA.)...

Many a helices have predominantly hydrophobic R groups on one side of the axis of the helix and predominantly hydrophilic ones on the other. These amphi-pathic helices are well adapted to the formation of interfaces between polar and nonpolar regions such as the hydrophobic interior of a protein and its aqueous envi-... 

Using Equations 3-3 and 3-4, we can plot f(0 vs. T 1/2 or T based on the experimental data on the jt-T characteristics (see Figure 12) [39]. Figure 13 indicates that Equation 3-3 is more realistic than Equation 3-4. The correlation coefficient, R, for Equation 3-3 is nearly unity, suggesting that the assumption of the "Coulombic" interaction between the hydrophilic head-groups is essential in the interpretation of the isotherm, especially for the low T(or the large A) region. 

In addition to the transport selectivities based on molecular charge or size described above, chemical interactions between the membrane material and the molecule to be transported can also strongly influence the rate and selectivity of transport. The introduction of chemically based transport selectivity was accomplished by chemisorbing thiols (RSH) to the Au tubule surfaces [113]. Membranes derivatized with two different R groups—the hydrophobic R = -CigHjj and the more hydrophilic (2)R = -C2H4-OH— were prepared. The rate and selectivity of transport in these membranes is dramatically altered by the chemical identity of the R group. 

A scale combining hydrophobicity and hydrophilicity of R groups it can be used to measure the tendency of an amino acid to seek an aqueous environment (- values) or a hydrophobic environment (+ values). See Chapter 11. From Kyte, J. Doolittle, R.F (1982) A simple method for displaying the hydropathic character of a protein. J. Mot. Biol. 157, 105-132. 

Knowledge of the chemical properties of the common amino acids is central to an understanding of biochemistry. The topic can be simplified by grouping the amino acids into five main classes based on the properties of their R groups (Table 3-1), in particular, their polarity, or tendency to interact with water at biological pH (near pH 7.0). The polarity of the R groups varies widely, from nonpolar and hydrophobic (water-insoluble) to highly polar and hydrophilic (water-soluble). 

A typical globular protein adopts a unique minimum energy conformation that is compact with few or no internal water molecules. Hydrophobic (nonpolar) R groups tend to be on the inside (away from water) and most hydrophilic (polar) R groups tend to be on the outside where they can be solvated by hydrogen bonding with H20. In the case of enzymes (proteins that catalyse specific chemical reactions) there may be special structural features of which the best known are active site depressions or grooves on the surface that bind the chemical substrates of the enzyme-catalysed reaction. 

Perfluoroalkyl compounds (PFCs) consist of a perfluoroalkyl chain (where all hydrogen atoms are replaced with fluorine atoms) and a hydrophilic end group, with the general strucmre F(CF2) R. The perfluoroalkyl chain may be of varying lengths, typically k = 4 to 15. Several specific classes of PFCs are discussed below. As research in this field continues and analytical standards and methods evolve, the number of PFCs observed in environmental samples continues to increase. 

Ether (-O-CR3) Hydrophilic at low temperatures, solubility and properties vary with R groups and tacticity... 

As a polypeptide is synthesized in a cell, its amino acid sequence might appear random (i.e., a few hydrophilic acids, followed by several lipophilic acids, then a number of hydrophilic ones, and so on). However, as the polypeptide folds and coils into a three-dimensional shape, it becomes apparent that this structure is controlled by the sequence of R groups. The polypeptide chain folds so that the... 

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