DNA Replication

How to copy a genome

DNA Replication

When: During S-phase of interphase

Where: 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

Prokaryotes1 origin

Eukaryotesmultiple origins

for each chromosomes

Terminology

Replication Bubbleseparated double helix

Replication Forkone at each end of bubble, where helix is

actively unzippedSemi-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 primerStep 3: ElongationStep 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

RNA Primase

Leading Strand

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

Nucleoside Tri-phosphate

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 1DNA Replication 2DNA Replication 3 – cool sounds