Dna
Essay by 24 • March 5, 2011 • 523 Words (3 Pages) • 1,040 Views
Because the original DNA strands are complementary and run antiparallel, only one new strand can begin at the 3' end of the template DNA and grow continuously as the point of replication (the replication fork) moves along the template DNA. The other strand must grow in the opposite direction because it is complementary, not identical to the template strand. The result of this side's discontiguous replication is the production of a series of short sections of new DNA called Okazaki fragments (after their discoverer, a Japanese researcher). To make sure that this new strand of short segments is made into a continuous strand, the sections are joined by the action of an enzyme called DNA ligase which LIGATES the pieces together by forming the missing phosphodiester bonds!
Image Source: http://esg-www.mit.edu:8001/esgbio/dogma/repl.html
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The last step is for an enzyme to come along and remove the existing RNA primers (you don't want RNA in your DNA now that the primers have served their purpose, do you?) and then fill in the gaps with DNA. This is the job of yet another type of DNA polymerase which has the ability to chew up the primers (dismantle them) and replace them with the deoxynucleotides that make up DNA. Here is a link with a diagram of the overall process of DNA replication of Okazaki Fragments.
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Since each new strand is complementary to its old template strand, two identical new copies of the DNA double helix are produced during replication. In each new helix, one strand is the old template and the other is newly synthesized, a result described by saying that the replication is semi-conservative. This process is shown schematically below. Crick described the DNA replication process and the fitting together of two DNA strands as being like a hand in a glove. The hand and glove separate, a new hand forms inside the old glove, and a new glove forms around the old hand. As a result, two identical copies now exist.
Image Source: http://esg-www.mit.edu:8001/esgbio/dogma/repl.html
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