19-10-2016, 02:09 PM
1459857853-DNAREPLICATION.pptx (Size: 1.55 MB / Downloads: 5)
Cell Division (mitosis) :-
Cells must copy their chromosomes (DNA synthesis) before they divide so that each daughter cell will have a copy
A region of the chromosome remains uncopied (centromere) in order to hold the sister chromatids together
Keeps chromatids organized to help make sure each daughter cell gets exactly one copy
Nondisjunction is when sister chromatids do not assort correctly and one cell ends up with both copies while the other cell ends up with none
DNA Synthesis :-
The DNA bases on each strand act as a template to synthesize a complementary strand
Recall that Adenine (A) pairs with thymine (T)and guanine (G) pairs with cytosine ©
The process is semi conservative because each new double-stranded DNA contains one old strand (template) and one newly-synthesized complementary strand
Leading Strand :-
Topisomerase unwinds DNA and then Helicase breaks H-bonds
DNA primase creates a single RNA primer to start the replication
DNA polymerase slides along the leading strand in the 3’ to 5’ direction synthesizing the matching strand in the 5’ to 3’ direction
The RNA primer is degraded by RNase H and replaced with DNA nucleotides by DNA polymerase, and then DNA ligase connects the fragment at the start of the new strand to the end of the new strand (in circular chromosomes)
Lagging Strand :-
Topisomerase unwinds DNA and then Helicase breaks H-bonds
DNA primase creates RNA primers in spaced intervals
DNA polymerase slides along the leading strand in the 3’ to 5’ direction synthesizing the matching Okazaki fragments in the 5’ to 3’ direction
The RNA primers are degraded by RNase H and replaced with DNA nucleotides by DNA polymerase
DNA ligase connects the Okazaki fragments to one another (covalently bonds the phosphate in one nucleotide to the deoxyribose of the adjacent nucleotide)
Origin of Replication :-
Begins at Origins of Replication
• Two strands open forming Replication Forks (Y-shaped region)
• New strands grow at the forks.