1. DNA Replication
How to copy a genome

2. 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

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

4. 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

5. Replication Overview

6. 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

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

8. 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

9. Step 1: Unwinding Double Helix
SS binding proteins

10. 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

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

12. 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

13. Step 3: Elongation

14. Nucleoside Tri-phosphates

15. 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

16. Step 4: Primer removal and Ligation

17. Enzyme Overview

18. Replication Overview

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