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Cell Replication 10/11/2011

When you look at someone, all you are seeing is the finished product of a very complicated and meticulous process known as DNA replication. Cells go through several stages and restriction points when they undergo cytokinesis. On of the most important and complicated processes occur in the S-Phase (synthesis) stage. DNA replication takes place in this phase.

There were three proposed models of how DNA is replicated and they are the dispersive model in which the original strand of DNA would produce two DNA molecules with sections of both old and new DNA along each new strand of DNA, the conservative model states that the original DNA molecule will remain intact but a completely new strand will generate but the most logically plausible model is the one we use today called the semi conservation model in which would produce molecules with both old and new DNA, but each molecule would be composed of one old strand and one new one.

In this semi conservation model, a DNA Helicase binds to DNA and unwinds the DNA molecule from itself. To maintain the stability of the DNA molecule, single-stranded DNA binding proteins bind to the exposed purines and pyrimidines. The double helix shape of the DNA have “gaps” of six to eight visible nucleotides that are called the DNA’s major grove region so that DNA Polymerase 3 can bind to the DNA molecule and begin the continuous replication process of the leading strand of the DNA molecule. DNA Polymerases 3 can only read from the 5’-3’direction and since DNA is antiparallel this makes replicating the lagging or the 3’-5’ end a little more complex. This 3’-5’ end forms in Okazaki fragments where a RNA primase attaches to this strand and lays down the RNA primer and then DNA Polymerase 3 comes and makes DNA in the 5’-3’ direction and then DNA Polymerase 1 comes in and converts the RNA primers into base complementary pair DNA and finally Ligase comes in to fill the gaps of each fragment and this is the continuous method is repeated until the whole lagging strand is replicated.

 
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Posted by on October 11, 2011 in Biology

 

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