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Published byBuck Walton Modified over 8 years ago
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Part 3 DNA Replication 24-1
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Learning Targets 5. Understand base pairing and its role in replication, transcription and translation. 6. Understand that replication is semi-conservative and occurs on a lagging and leading strand. 7. Know the role of enzymes in replication including helicase, primase, DNA polymerase and ligase. 24-2
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24-3 DNA Replication Found only in the nucleus Origin of replication Multiple origins on a chromosome Occurs during S phase of the cell cycle Semiconservative each new DNA strand has 1 new/1 old strand
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DNA Replication Enzymes DNA helicase unzips DNA unwinds it At “replication fork” “unzipped” bases form H bonds with “free” nucleotides Primase assembles RNA Primer “seats” DNA Polymerase DNA polymerase bonds sugar to phosphate makes new strand of DNA (DNA Ligase (see Okazaki Fragments)) 24-4
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24-5 Accuracy DNA Polymerase also “proofreads” Very accurate (only 1 error every billion nucleotides!) 20 repair enzymes “edit” goofs mutagens (heat, chemicals, radiation, etc.) EXACT SEQUENCE is VERY IMPORTANT
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24-6 Okazaki fragments DNA is “anti-parallel” Sugar/phosphate groups “point” in diff. direction 5’ 3’ “leading strand” 3’ 5’ “lagging strand” DNA Polymerase only assembles new strand in 5’ 3’ direction Leading strand is OK Lagging strand forms in segments Okazaki fragments DNA Ligase ties sugar/phosphates together
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