Chain sequence length, size

Figure 3 Left panel Typical distributions of H and P monomeric units along the chain for regular (mulfiblock) sequence having fixed block lengfh of 8 units, as well as for purely random sequence with average block length L=2. nandom-blocky sequence with /.=6.4, and protein-like sequence with L=6.4. The H units are denoted as +1 and the P units as -1. Right panel Variance of the number of different monomeric units in the fragment of sequence of size A for protein-like, random, and random-blocky copolymers. The sequence length /V=1024.

Figure 1.3 The copolymers illustrated are (a) statistical copolymer, (b) alternating copolymer, (c) linear segmented block copolymer in which the block sequence lengths are the same, and (d) a graft copolymer in which grafted chains are the same size. All the polymers illustrated have a 50/50 composition of the two components and all have the same degree of polymerization (total number...

When polymer chains overlap, they take conformations that are different from those of isolated individual chains because monomers interact in a different way. Figure 2.22 schematically shows the conformation of a polymer chain in a concentration well above the overlap concentration. It has a structure like a pearl-necklace a train of blobs (called a concentration blob) made up of groups of monomers connected in sequence. The size of each concentration blob is called the correlation length f. The monomers in the blob are directly in contact with the solvent so that they swell by the excluded-volume effect, in the same way as an isolated random coil does. 

In the studies described above on FAD of labelled polybutadiene, the type of orientation autocorrelation function able to account for the experimental results has been defined. However, no information has been obtained about the size of the chain sequence involved in the motion observed by FAD of labelled polybutadiene. In order to obtain an estimate of this sequence length, FAD measurements have been performed (41) on various 9,10 dialkylanthracene probes (Fig. 18), denoted C, with n varying. 

For a polypeptide chain of 100 residues in length, a rather modest size, the number of possible sequences is 20 , or because 20 = lO, lO unique possibilities. These numbers are more than astronomical Because an average protein molecule of 100 residues would have a mass of 13,800 daltons (average molecular mass of an amino acid residue = 138), lO such molecules would have amass of 1.38 X lO " daltons. The mass of the observable universe is estimated to be 10 proton masses (about 10 daltons). Thus, the universe lacks enough material to make just one molecule of each possible polypeptide sequence for a protein only 100 residues in length. 

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