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Transcript
Chapter 21 DNA Replication Objectives • Explain the importance of DNA replication in cell reproduction DNA replication • During interphase S: DNA is duplicated prior to mitosis. • Each parent strand serves as a template for making a copy of a new strand of DNA. • It is semiconservative because each parent strand is conserved in one of two DNA strands. Replication • DNA helicase enzyme breaks the hydrogen bonds between AT and CG • DNA polymerase enzyme adds new DNA nucleotides, which are always present in the nucleus to the complementary strand. • Adenine bonds to Thymine, and Cytosine bonds to Guanine. • • • • • • • Ligase enzyme binds or seals breaks in the sugar-phosphate backbone. RNA primase lays a starting sequence. 3’ to 5’ direction lagging strand. 5’ to 3’ direction is the leading strand. Okazaki fragments are made on the lagging strand. DNA returns to a coiled structure. Two identical DNA strands are made. • Takes about 8 hours to complete 3 billion base pairs. • https://www.youtube.com/watch?v=dKubyIRiN84 Mutations • Sometimes an errors occurs where one base mistakenly pairs with a wrong base. • Cell enzymes repair most mistakes. • Mutations can be good or bad for the organism. • Variation makes you different than your neighbor.
