Overview of How DNA Copies Itself 1 DNA

Overview of How DNA Copies Itself 1. DNA helix begins unwinding 2. Helicase enzyme untwists the double helix 3. The enzyme primase puts down a short piece of RNA termed the primer 4. DNA polymerase reads along each single DNA strand adding the complementary nucleotide A -T and C-G 5. Each nucleotide strand serves as a template for building a new complementary strand (semiconservative replication) 6. DNA ligase seals and checks PLAY DNA Replication Overview

How nucleotides are added in DNA replication Template strand HO 3’ Sugarphosphate backbone New strand HO 3’ 5’ 5’ C O A O T P O T A O C P 3’ A O OH O A P P T O P O 5’ P O OH T G O P P O O 5’ G O A P P O T A DNA polymerase A P A O P O O C P O P P G O P T C P G O P Template strand 3’ P Pyrophosphate OH

Summary of How DNA Copies Itself § The process of DNA replication can be summarized as such § The enzyme helicase first unwinds the double helix § The enzyme primase puts down a short piece of RNA termed the primer § DNA polymerase reads along each naked single strand adding the complementary nucleotide DNA polymerase can only build a strand of DNA in one direction The leading strand is made continuously from one primer The lagging strand is assembled in segments created from many primers

DNA Replication § Since DNA polymerase only works in one direction: § A continuous leading strand is synthesized § A discontinuous lagging strand is synthesized § DNA ligase splices together the short segments of the discontinuous strand § This process is called semiconservative replication

DNA Replication (cont. ) RNA primers are removed and replaced with DNA Ligase joins the ends of newly-synthesized DNA Mechanisms exist for DNA proofreading and repair