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DNA Replication. During DNA Replication, an exact copy of DNA is made. Replication of DNA occurs during the S Phase of Interphase during the cell cycle. Each strand of DNA holds specific information to create the other strand in the base-pairing pattern. But….how does it replicate?.

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Dna replication
DNA Replication

  • During DNA Replication, an exact copy of DNA is made.

  • Replication of DNA occurs during the S Phase of Interphase during the cell cycle.

  • Each strand of DNA holds specific information to create the other strand in the base-pairing pattern.


But how does it replicate
But….how does it replicate?

  • Conservative Model

  • Semiconservative Model

  • Dispersive Model



Dna replication1
DNA Replication

  • Replication occurs in segments, call replication bubbles.

  • Each new strand consists of one old strand and one new strand, making it a semi-conservative process.


Steps to replciate dna
Steps to replciate DNA

  • There are numerous replication bubbles along a strand of DNA

  • Helicase unwinds the DNA at the replication fork.

  • Single strand binding proteins bind to the separate strands to stabilize them


  • Topoisomerase – helps relieve the strain ahead of the replication fork


Fig. 16-12b

Origin of replication

Double-stranded DNA molecule

Parental (template) strand

Daughter (new) strand

0.25 µm

Replication fork

Bubble

Two daughter DNA molecules

(b) Origins of replication in eukaryotes


Fig. 16-13

Primase

Single-strand binding proteins

3

Topoisomerase

5

3

RNA primer

5

5

3

Helicase


  • RNA Primase creates an RNA primer (5-10 nts long)

  • DNA polymerase adds nucleotides to preexisting DNA chain. This is done in the 5’ to 3’ direction. (Leading strand)

  • Lagging strand is created discontinuously is segments. (Okasaki fragments )


  • Okasaki fragments 1000-2000nt in prokaryotes and 100-200 in eukaryotes

  • Nucleotides added 500nt/sec in bacteria and 50nt/sec in humans

  • DNA polymerase I removes the primer nucleotides and replaces with DNA nucleotides

  • DNA ligase joins the sugar phosphate backbones of Okasaki fragments


A closer look at dna replication
A closer look at DNA replication

  • How Nucleotides are added

  • Replication Fork


Thank goodness for spell check
Thank goodness for spell check!

  • Proofreading Enzymes repair damaged or mismatched nucleotides

  • What causes the damage?


Interesting fact chromosome s
Interesting Fact!Chromosome s…

  • DNA and protein material

  • Bacterial chromosome consists of approximately 4.6 million nucleotides and 4400 genes

  • Humans have approximately 1000 gene/chromosomes.


Interesting fact telomeres telomerase
Interesting Fact!Telomeres/Telomerase…

  • Protects our genes

  • TTAGGG repeats of 100x – 1000x

  • Telomerase protects cells from shortening during division by lengthening the ends. Found in gametes and a few somatic cells



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