DNA Replication How to copy a genome

DNA Replication When: Where: How: Result: During S-phase of interphase Prokaryotes – in nucleoid region Eukaryotes – in the nucleus How: Starts at origin of replication Uses a variety of proteins Result: Two identical DNA molecules

Origin of Replication Where replication begins Prokaryotes Eukaryotes multiple origins for each chromosomes

Terminology Replication Bubble Replication Fork Semi-conservative separated double helix Replication Fork one at each end of bubble, where helix is actively unzipped Semi-conservative each new helix contains half of the parent strand

Replication Overview

Enzymes involved in Replication DNA Polymerase I replaces RNA primer with DNA DNA Polymerase III adds DNA nucleotides to elongating strand DNA Ligase connects DNA backbones RNA Primase adds RNA primer Helicase unzips double helix Single-Strand Binding Proteins keeps helix separated

Steps in DNA replication Step 1: Unwinding DNA Step 2: Addition of RNA primer Step 3: Elongation Step 4: Primer removal and Ligation

Step 1: Unwinding DNA Helicase attaches to double helix, unwinds DNA, and separates complimentary base pairs Single-strand binding proteins attach to DNA to prevent helix reforming

Step 1: Unwinding Double Helix SS binding proteins

Step 2: Addition of RNA primer RNA primase adds RNA primer to lagging strand RNA primer: short RNA nucleotide molecule complimentary to template strand Template (parent) strand: pre-existing DNA stand

Step 2: Addition of RNA primer Leading Strand RNA Primase Lagging Strand

Step 3: Elongation DNA polymerase III adds DNA nucleoside triphosphates complimentary to templates strand Lagging strand – DNA polymerase III starts elongation at RNA primer Polymerase works only in the 5’  3’ direction

Step 3: Elongation

Nucleoside Tri-phosphates

Step 4: Primer removal and Ligation DNA polymerase I removes RNA primer and replaces RNA nucleotides with DNA nucleotides DNA backbone between fragments are joined (ligated) by DNA ligase

Step 4: Primer removal and Ligation

Enzyme Overview

Replication Overview

Animation DNA Replication 1 DNA Replication 2 DNA Replication 3 – cool sounds