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9: Details of DNA Replication and Repair
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9.1: Introduction
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Replication begins at one or more origins of replication along DNA, where helicase enzymes catalyze unwinding of the double helix. DNA unwinding creates replicating bubbles, or replicons, with replication forks at either end. Making a new DNA strand starts with making an RNA primer with RNA nucleotides and primase enzymes.
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9.2: DNA Replication
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As we’ve seen, DNA strands have directionality, with a 5’ nucleotide-phosphate and a 3’ deoxyribose hydroxyl end. This is even true for circular bacterial chromosomes…, if the circle is broken! Because the strands of the double helix are antiparallel, the 5’ end of one strand aligns with the 3’end of the other at both ends of the double helix. The complementary pairing of bases in DNA means that the base sequence of one strand can be used as a template to make a new complementary strand. As we’l
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9.3: DNA Repair
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We generally accept the notion that replication faithfully duplicates the genetic material. At the same time, evolution would not be possible without mutation, and mutation is not possible without at least some adverse consequences. Germline mutations are heritable. When present in one, but especially in both alleles of a gene, such mutations can result in genetic disease (e.g., Tay-Sach’s disease, cystic fibrosis, hemophilia, sickle-cell anemia, etc.).
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9.4: Key Words and Terms
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