1. DNA Replication

2. DNA Structure Nucleic acid Double Helix (2 strands of DNA)
Nucleotide – sugar, phosphate group and a base
Complementary strands pair up (Adenine & Thymine, Cytosine & Guanine)
Base pairs held together by hydrogen bonds
Strands are antiparallel (5’ - 3’ and 3’ – 5’)

3. Nucleus

4. Nucleus
Nuclear envelope is a double membrane and has two overlapping phospholipid bilayers with nuclear pores
Chromatin – total DNA and proteins in nucleus
Nucleolus – ribosome subunits are made here

5. Chromosomes
Chromosomes – single DNA molecule wrapped around histone proteins, then coiled into chromosome cylinders.
Humans have 46 chromosomes
One pair of sex chromosomes (XX – girls and XY – boys)
22 pairs of Autosomes - all other chromosomes

6. DNA Replication
Basic Concept = create a new strand by matching nucleotides to an existing strand

7. DNA Replication
Replication is semi-conservative (one strand is old, one strand new)

8. General Process of DNA Replication
Step 1: Initiator Proteins bind to origins of replication to begin replication
Attracts other enzymes involved in replication process
Step 2:
DNA Helicase separates the DNA helix

9. Question…
What kind of bonds does Helicase break?
Hydrogen bonds

10. General Process
Primase
RNA Primer
Step 3: Primase builds an RNA primer at the starting from the 5’ end of the new DNA strand
Uses the 3’ end of existing DNA strand
Why? Because the DNA Polymerase (main DNA building enzyme) needs something to build off of 3’ 5’
DNA Polymerase III

11. General Process
Step 4: DNA Polymerase builds the new strand of DNA in a 5’ to 3’ direction by adding matching nucleotides

12. Problem…
How can both strands of DNA be replicated in a 5’- 3’ direction at the same time they are antiparallel?
Answer: leading and lagging strands

13. Leading and Lagging Strands
Leading strand is synthesized continuously in the direction of replication (goes in the same direction as helicase)
Lagging strand is synthesized in short fragments the opposite direction of replication (opposite direction as helicase)
DNA Ligase seals DNA fragments together

14. Lagging Strand

15. Finishing DNA Replication
Problem #1: There are still RNA nucleotides in the DNA (primers)
Solution = DNA Polymerase cuts out the RNA nucleotides and replaces them with DNA

16. SSBs
DNA
Polymerase III
Helicase
Leading Strand
DNA Ligase
DNA
Polymerase I
Primase
DNA Pol
III
Lagging
Strand
Primer