Question

Question 27 How is the cell able to repair 99% of the errors made by the DNA polymerase during replication? With methyl groups that mark where mutations happen With semiconservative replication, the original strand can be compared to the new stran With conservative replication the new faulty DNA strands are destroyed With special enzymes that identify Indels • Previous No new data to save. Last checked

Answer 1

With semiconservative replication,the orginal strand can be compared to the new strand

DNA polymerases are the enzymes that build DNA in cells. During DNA replication (copying), most DNA polymerases can “check their work” with each base that they add. This process is called proofreading. If the polymerase detects that a wrong (incorrectly paired) nucleotide has been added, it will remove and replace the nucleotide right away, before continuing with DNA synthesis.

10 GTA GT3'T TILL с IT ILIILIT A I Polymerase adds an incorrect nucleotide to the new strand of DNA. T C 5' 5 G GTA GT I IIIIIIIIIIIIII C CAT CAGIC Polymerase detects that bases are mispaired. 3 [ 5 5' 3 G GIA GI. IIIIIIIIIIIIIII CCA I C A GI C Polymerase uses 3'-5' exonuclease activity to remove incorrect nucleotide. 5

Many errors are corrected by proofreading, but a few slip through. Mismatch repair happens right after new DNA has been made, and its job is to remove and replace mis-paired bases (ones that were not fixed during proofreading). Mismatch repair can also detect and correct small insertions and deletions that happen when the polymerases "slips," losing its footing on the template.First, a protein complex (group of proteins) recognizes and binds to the mispaired base. A second complex cuts the DNA near the mismatch, and more enzymes chop out the incorrect nucleotide and a surrounding patch of DNA. A DNA polymerase then replaces the missing section withcorrect nucleotides, and an enzyme called a DNA ligase seals the gap.

new DNA 5' IIIIIIIIIIIIIII D I IIIIIIIIIIIIIII NON S A mismatch is detected in newly synthesized DNA. 5 template | 11 IIIIIIII OONO The new DNA strand is cut, and the mispaired nucleotide and its neighbors are removed. TONINI replacement ONA in T ILI IL ON A U N T LII II III III he missing patch is replaced with correct nucleotides by a DNA polymerase. I mn t sealed gap in IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII A DNA ligase seals the gap in the DNA backbone. ñ 5'

In bacteria, original and newly made strands of DNA can be told apart by a feature called methylation state. An old DNA strand will have methyl groups attached to some of its bases, while a newly made DNA strand will not yet have gotten its methyl group.In eukaryotes, the processes that allow the original strand to be identified in mismatch repair involve recognition of nicks (single-stranded breaks) that are found only in the newly synthesized DNA.