(c)+DNA+Replication+(Q+10-13)



DNA replication is the process of making a exact copy of the DNA of an organism in order to pass the genes on to its offspring or to use the existing DNA as a blueprint for synthesizing new cells. This means that DNA replicates into an identical copy so that characteristics can from a parent can be passed onto the offspring. Without DNA replication, there will be no information that can be followed to create new organism. The replication of DNA is a vital part during cell division and the growth of an organism, and it is done through a process called mitosis, this is when a mother cell splits into two daughter cells.

The base pairing rules:

DNA molecules are made up of nucleotides. Each nucleotide is made up of a base and a backbone constructed of sugar and phosphate. The four different bases which can be found include: Adenine, Cytosine, Thymine and Guanine - often just called by their initials. The base pairing rule is the rule which states that only a certain base can be paired up with another and this helps in a more precise and accurate DNA replication. The base pairing rule states that Adenine can only be paired with Thymine (and vice versa) and Cytosine can only be paired with Guanine (and vice versa).

**Note:** //Cell division// - growth occurs by an increase in the number of cell or a (limited) increase in cell size. Increase in cell number takes place as a result of cell division, which frequently occurs during the development of a plant or animal.

The double helix (see definition below) of the DNA unwinds with the help of the enzyme called //helicase// and seperates in half. Each strand is made of 4 different types of nucleotides: Thymine (T), Cytosine (C), Adenine (A), and Guanine (G). Each nucleotide has a pair that it also connects with, for example if A is on strand, T will always be on the other strand to pair with A. Similary C always pairs with G. //This is like a twisted zipper (double helix) which unwinds itself and then unzips.//

**Note:** //double helix// - refers to the structure of the DNA which is double stranded.



The 2 seperated strands are called the leading strand and lagging strand. Single stranded DNA binding proteins prevent the strands from winding together again. //These are like the two strands of the zipper.//



The seperated strands each form a new DNA by with the help of the enzyme called //DNA polymerse III// which finds the matching pair for each nucleotides (A,T),(C,G). //Each of the sides of the zipper consist of the different nucleotide bases, these bond with their partner base according to the base pairing rules (see above). A special enzyme helps to bond the zipper together, called// DNA ligase I//.//

As the matching nucleotides bond with the original strand, an other strand forms and it becomes a double helix again. //For each new zipper of DNA there is one half of the original strand and one new set of bases. This then twists again to form the double helix.// The end product is 2 identical spirals of DNA. //One of these spirals will now leave the nucleus of the original cell and go to a new cell, the new cell an exact replica of the original cell.//

There is a good animation which you could also look at: [] media type="youtube" key="yqESR7E4b_8" width="676" height="374"
 * Process of DNA Replication**

Sources:

"Nucleic Acid Double Helix." // Wikipedia //. Wikimedia Foundation, 22 May 2012. Web. 27 May 2012. .

"DNA Replication." // DNA Replication //. Web. 27 May 2012. .

"Base-pairing Rules." // Dictionary.com //. Web. 27 May 2012. . Steane, Richard. "Cell Division & Chromosomes." // BioTopics //. Web. 27 May 2012. .