What prevents ribonucleotides from being incorporated into the growing DNA stran
ID: 54870 • Letter: W
Question
What prevents ribonucleotides from being incorporated into the growing DNA strand during replication of the genome? In what aspect of replication are ribonucleotides used, and what ultimately happens to them? What prevents ribonucleotides from being incorporated into the growing DNA strand during replication of the genome? In what aspect of replication are ribonucleotides used, and what ultimately happens to them? What prevents ribonucleotides from being incorporated into the growing DNA strand during replication of the genome? In what aspect of replication are ribonucleotides used, and what ultimately happens to them?Explanation / Answer
DNA Polymerases (mainly the DNA polymerase III for prokaryotes) prevents the incorporation of the ribonucleotides into the growing DNA strand during replication. There are generally two conserved amino acid residues present in the nucleotide binding pocket of the DNA polymerase whose side chains occupy the space that will, otherwise, be required to accomodate the 2'-OH group of a ribonucleotide (in case a ribonucleotide is incorporated in that pocket). This is generally termed as Steric Gate mechanism - this mechanism prevents the ribonucleotides sterically from entering the DNA polymerase pocket & hence they are not incorporated in the DNA strand durng replication ( DNA polymerases are the main enzymes that mediate DNA replication.).
Ribonucleotides are required for the generation of primers which are synthesized by Primase - primers are essential for the initiation of replication of both the lagging & the leading strands; since the DNA polymerases need a free 3'-OH group at the end of the nucleotide so that it can add another deoxyribonucleotide at its end.
Primers made of ribonucleotides are replaced by deoxyribonucleotides by the process of Nick Translation- mediated by DNA polymerase I. The primer i.e. a RNA strand paired to a DNA template is simultaneously degraded by the 5’-3’exonuclease activity & replaced by the 5’-3’polymerase activity of DNA polymerase I.
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