Fidelity of Replication

Mismatch Repair Correction of the rare mismatches left after replication in E. coli improves the overall fidelity of replication by an additional factor of 102 to 103. The mismatches are nearly always corrected to reflect the information in the old (template) strand, so the repair system must somehow discriminate between the template and the newly synthesized strand. The cell accomplishes this by tagging the template DNA with methyl groups to distinguish it from newly synthesized strands. The mismatch repair system of E. coli includes at least 12 protein components (Table 25-5) that function either in strand discrimination or in the repair process itself. 

Fidelity of Replication of DNA What factors promote the fidelity of replication during the synthesis of the leading strand of DNA Would you expect the lagging strand to be made with the same fidelity Give reasons for your answers. 

A final check of the fidelity of replication is made after a new strand has been formed. Mismatched base pairs are identified, and the incorrect nucleotides are cut out and replaced by correct ones.655 670 681 683 Some of the thymine dimers created by the action of light are also repaired photochemically by photolyases (see Chapter 23). Photoreactivation was the first DNA repair process recognized.684 However, most thymine... 

Many polymerases further enhance the fidelity of replication by the use of proofreading mechanisms. As already noted, the Klenow fragment of E. coli DNA polymerase I includes an exonuclease domain that does not participate in the... 

The fidelity of replication is very high with an overall error rate of 10 9 to 10 1°. 

Since the proposal of the double helical structure of DNA, it has been recognized that the fidelity of replication of genetic information depends on the hydrogen bonding interaction between the purine and pyrimidine bases of DNA, i.e., the cytosine-guanine and thymine-adenine complementarity. The importance of hydrogen bonds for fidelity depends on two... 

Pol I has several enzymatic activities other than its ability to polymerize one of these is important in maintaining continuity of the daughter strand, and the other improves the fidelity of replication. These two functions are a 5 -> 3 exonuclease activity and a 3 -> 5 exonuclease activity. 

SOS repair includes a bypass system that allows DNA chain growth across damaged segments at the cost of fidelity of replication. It is an error-prone process even though intact DNA strands are formed, the strands are often altered. 

Two cellular systems aid the fidelity of replication. These include the following ... 

A final check of the fidelity of replication is made after a new strand has been formed. Mismatched base pairs are identified, and the incorrect nucleotides are cut out and replaced by correct Some... 

Recall What ensures fidelity in protein synthesis How does this compare with the fidelity of replication and transcription ... 

The virtuosity of the DNA polymerase first isolated from E. coli still amazes me. Holding one or two turns of one chain of DNA helix as template, it assembles a complementary chain thousands of nucleotides long. It does so by Watson-Crick base pairing with an accuracy which exceeds chemical predictions. The enzyme achieves this fidelity of replication by a proof-reading exonuclease in its active center. This 3 5 exonuclease... 

This scheme (Fig. 2.5) thus shows how oligonucleotides can direct the synthesis of polypeptides in the absence of protein or ribosomal machinery and, as such, is an appealing bioorganic model for the origin of prebiotic protein synthesis (see Section 3.7.2.1). Indeed, it seems most probable that primitive biosystems used a similar concept to carry out primitive protein synthesis where Watson-Crick base pairing provided the intrinsic mechanism for achieving fidelity of replication and direction of protein synthesis. In time, the carrier oligonucleotides could have evolved into more efficient species such as the present-day tRNA molecules. 

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