DNA replication

1. 12-2 chromosomes and DNA replication
• DNA:
– Prokaryotic cell:
• Naked, in cytoplasm, no nucleus
• Single circular DNA
• No complex with histone Bases on the chromosome
– eukaryotic cell:
• In nucleus,
• In the form of chromosome
Chromosome
E. coli bacterium

2. • Chromosome structure:
– Chromatin : DNA + proteins
– Chromosome : supercoiled chromatin
– Nucleosome
• beadlike structures in chromosome formed by DNA and histone
molecules
• Help to fold long DNA into tiny cell nucleus
Chromosome Nucleosome
DNA
double
helix
Coils
Supercoils
Histones

5. • DNA replication (in interphase of mitosis or meiosis)
– Prokaryotic cell:
• Begins at a single point
• Proceeds in two directions

6. • DNA replication (in interphase of mitosis or meiosis)
– Eukaryotic cell:
• Begins at many sites
• Proceeds in two directions

8. • DNA replication
– Semi-conservative replication
• During DNA replication, the DNA double helix separates into two
strands. Each strand serves as a template to produces two new
complementary strands following the rules of base pairing.
Parent
DNA
Copy

15. • DNA replication
– Steps
• Unzip (form replication fork)
• Strands assembled in the 5’ to 3’ direction
(Continuous and Discontinuous, form okazaki fragments)
• 2 identical DNA molecules
replication fork
AHL

16. AHL

17. • DNA replication
– Enzyme envolved
Helicase: unzips DNA.
Primase: add short RNA primers.
Single-strand binding protein : hold seperated strands apart
DNA polymerase :
DNA polIII: attaches complementary nucleotides & proofreading
DNA pol I: replaces RNA primers with DNA nucleotides.
DNA ligase: seal okazaki fragments
AHL

18. AHL