Determining the Method of DNA Replication Replication of DNA Determining the Method of DNA Replication

DNA Replication What is replication? “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.”, Watson and Crick

Overview of DNA Replication Helicase unwinds the DNA Replication bubbles form Complementary base pairs inserted DNA polymerase Joining DNA ligase

Which Type of Replication Occurs? Conservative Parental strands get back together Semiconservative Parental strands serve as template Dispersive Copy short chunks

Types of Replication

Meselsen and Stahl’s Experiment They made predictions for each possible type of replication They conducted experiment and gathered data Their conclusion was made by comparing results to predictions

Predictions of DNA Band Location for Each Type of Replication Semiconservative Dispersive Conservative L I H P1 (0 Gen) X F1 (1 Gen) X X F2 (2 Gen) X X

Experimental Results Showing Band Locations The Experiment

Replication of DNA DNA replication is the process of copying a DNA molecule. Replication is semiconservative, with each strand of the original double helix (parental molecule) serving as a template (mould or model) for a new strand in a daughter molecule. 10

Replication: Eukaryotic DNA replication begins at numerous points along linear chromosome DNA unwinds and unzips into two strands Each old strand of DNA serves as a template for a new strand Complementary base-pairing forms new strand on each old strand Requires enzyme DNA polymerase 11

Replication: Eukaryotic Replication bubbles spread bi-directionally until they meet The complementary nucleotides join to form new strands. Each daughter DNA molecule contains an old strand and a new strand. Replication is semiconservative: One original strand is conserved in each daughter molecule i.e. each daughter double helix has one parental strand and one new strand. 12

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Science Focus: Aspects of DNA Replication Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. OH P is attached here 5¢ base is attached here CH2 O OH 4¢ C H H C 1¢ 1 H 3¢ C C H 2¢ OH H Deoxyribose molecule 2 DNA polymerase attaches a new nucleotide to the 3 carbon of the previous nucleotide. 5¢ end P T P A P P G C 3¢ end P P C G 5¢ P 3¢ P T A P C G P template strand DN A polymerase 3¢ end 5¢ end P 4 leading new strand template strand Direction of replication new strand 3¢ 3 helicase at replication fork RNA primer template strand 6 Okazaki fragment 3¢ 5 lagging strand 5¢ 5¢ parental DN A helix 7 DNA ligase DNA polymerase 3¢ Replication fork introduces complications 14

Replication: Prokaryotic Prokaryotic Replication Bacteria have a single circular loop Replication moves around the circular DNA molecule in both directions Produces two identical circles Cell divides between circles, as fast as every 20 minutes 15

Replication: Prokaryotic vs. Eukaryotic Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. origin replication is complete replication is occurring in two directions a. Replication in prokaryotes replication fork replication bubble parental strand new DNA duplexes daughter strand b. Replication in eukaryotes 16