DNA Replication 52 Exercise B: DNA Replication (con\'t) Repairing mistakes Cytos
ID: 194434 • Letter: D
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DNA Replication 52 Exercise B: DNA Replication (con't) Repairing mistakes Cytosine SSBP ONA Polymerase Illis extremely accurate. Another DNA Adenine Polymerase acts as a proof reader, DNA Polymerase ". In-Guanine Once replication is complete, DNA Polymerase II travels- Thymine down the entire link of the parental DNA strands looking D. Uracil for mismatched base pairs. Once it detects a mismatch, -Helicase @. DNA Polymerase l DNA Polymerase II .. DNA Polymerase la Deoxyribose . Primase -Ribose , Ligase -phosphate Telomerase new DNA strand and replaces it with the D-nucleotide complementary to the parental strand (Fig. 17). However, even this proofreading step is not completely accurate, missing mismatched base pair occurs approximately one out every billion times. These mistakes lead to nucleotide-level mutations. Suc h mutations are the only way in which new alleles are generated, and are usually neutral or deleterious relative to fitness. Occasionally t phenotypes allowing these organisms higher probability of surviving and reproducing. Such mutations tend to amplify in future generations due to natural selection. itERHAHHHI 5 3 Fig. 17. DNA Polymerase II proofreads the final replicated DNA strands. E In Fig. 17, play the part of DNA Polymerase Il. Scan the replicated DNA strands and find the mismatched base pair. Place a circle around it and replace the mismatched D-nucleotide with the correct one by writing the correct letter corresponding to the specific D-nucleotide and draw an arrow to where it should be input. 5" Fig. 18. Replicated and proof-read DNA strands why is the lagging strand longer than the leading strand? 8. Why are there unreplicated nucleotides on the lagging strand of the finalized replicated DNA? www.thebiologyprimer.comExplanation / Answer
7. LAGGING STRAND SYNTHECISED IN THE FORM OF FRAGMENTS CALLED OKAZAKI FRAGMENTS. WHILE SYNTHECIZING LAGGING STRAND, THERE IS NEED OF REVERSE THE DIRECTION OF THE LAGGING STRAND TEMPLATE BY FOLDING. THIS IS BECAUSE ONLY SINGLE DNA POLYMERASE CAN SYNTHECIZE BOTH STRANDS AT A TIME, EVENTHOUGH THE STRANDS ARE IN ANTIPARELLAL MANNER. MOREOVER DNA POLYMERASE SYNTHECIZE DNA IN 5'----------> 3' DIRECTION ONLY. SOME TIMES MOSTLY AT THE ENDS OF THE LAGGING STRAND TEMPLATE, IT IS NOT POSSIBLE TO FOLD AS IT CONTAIN FEW BASE PAIRS. IF IT IS NOT SYNTHECIZED, THE CHROMOSOME PROGRESSIVELY SHORTENED. TO PREVENT THIS, TELOMERASE ENZYME EXTEND THE LAGGING STRAND TEMPLATE SEVERAL BASES LENGTH THAN LEADING STRAND TEMPLATE. IF IT OCCUR SEVERAL TIMES, AUTOMATICALLY, THE LAGGING STRAND IS LONGER THAN LEEDING STRAND
8. MOSTLY AT THE ENDS OF THE LAGGING STRAND TEMPLATE, IT IS NOT POSSIBLE TO FOLD AS IT CONTAIN FEW BASE PAIRS. THIS IS WHY LAGGING STRAND TEMPLATE CONTAIN UN REPLICATED NUCLEOTIDES. THIS PROBLEM IS RESOLVED BY TELOMERASE AND PREVENT PROGRESSIVE SHORTENING OF THE CHROMOSOME
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