8. Conclusion
DNA replication is a biological process that occurs in all living organisms and copies their DNA; it is the basis for biological inheritance.
Before a cell enters the process of mitosis, its DNA replicates itself. Equal copies of the DNA pass into the daughter cells at the end of mitosis. In human cells, this means that 46 chromosomes (or molecules of DNA) replicate to form 92 chromosomes.
DNA replication is significant in the reproduction of cells through the mechanisms of mitosis and meiosis. The DNA replicates so that there will be an extra DNA when the cell multiplies, allowing the "daughters" the chance to reproduce.
DNA replication allows genetics to carry on, by replicating DNA, genetic information is passed on, allowing for offspring. Also, replicating DNA shows how genes are carried on through generations and how they undergo mutations and changes. Without DNA replication, there would be no such thing as genetics because nothing could reproduce.
DNA replication takes place at a Y-shaped structure called a replication fork. A self-correcting DNA polymerase enzyme catalyzes nucleotide polymerization in a 5′-to-3′ direction, copying a DNA template strand with remarkable fidelity. Since the two strands of a DNA double helix are antiparallel, this 5′-to-3′ DNA synthesis can take place continuously on only one of the strands at a replication fork (the leading strand). On the lagging strand, short DNA fragments must be made by a “backstitching” process. Because the self-correcting DNA polymerase cannot start a new chain, these lagging-strand DNA fragments are primed by short RNA primer molecules that are subsequently erased and replaced with DNA.
DNA replication requires the cooperation of many proteins. These include (1) DNA polymerase and DNA primase to catalyze nucleoside triphosphate polymerization; (2) DNA helicases and single-strand DNA-binding (SSB) proteins to help in opening up the DNA helix so that it can be copied; (3) DNA ligase and an enzyme that degrades RNA primers to seal together the discontinuously synthesized lagging-strand DNA fragments; and (4) DNA topoisomerases to help to relieve helical winding and DNA tangling problems. Many of these proteins associate with each other at a replication fork to form a highly efficient “replication machine,” through which the activities and spatial movements of the individual components are coordinated.
References
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Berg JM, Tymoczko JL, Stryer L, Clarke ND (2002). Biochemistry. W.H. Freeman and Company. ISBN 0-7167-3051-0. Chapter 27, Section 2: DNA Polymerases Require a Template and a Primer
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Internet resources:
http://en.wikipedia.org/wiki/DNA_replication
http://www.ncbi.nlm.nih.gov/books/NBK26850/