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

What is DNA replication? Write a good definition of this.
DNA replication is the biological process that occurs within the nucleus of all living organism where a DNA molecule is copied to make two identical molecules. This production of exact DNA copies is so that the organism can pass on its genes to its offspring or used to synthesize new cells. This replication is extremely important in the development of organisms, and is performed through the process of cell division known as mitosis, when a mother cell splits itself in order to produce two daughter cells. It is also vital that DNA replication is carried out accurately to prevent the organism from being harmed

Base-pairing rule:
DNA molecules are made up of nucleotides (bases) that are attached to backbones made of sugar and phosphate. There are four different bases in a DNA, adenine (A), cytosine (C), guanine (G) and thymine (T), all of which come in pairs. Because there is a base-pairing rule (meaning that a certain base must be paired with another), the coding of bases on one side of the double helix can immediately help determine the bases that must be on the other side. This feature allows for accurate DNA replication. The base-pairing rule is as follows:
 * A pairs with T
 * G pairs with C
 * C pairs with G
 * T pairs with A

Steps to DNA replication:
Each strand acts as a template for the production of the complementary strand and because the DNA strand twists and rotates a lot during the replication, another class of enzymes called the Topoisomerase cuts and rejoins the strand to prevent tangling. **Step 2:** As mentioned previously, a DNA has contains pairs of nucleotides or bases, each one attached to one side of the double helix (one strand). A DNA is replicated when one separated strand is matched with the respective strand that has got the corresponding nucleotides (refer to base-pairing rules). This process is carried out with the help of the DNA polymerase III enzyme which helps the strand find the other corresponding match and the DNA ligase enzyme which attaches the two matching nucleotides, forming a completed double helix strand of DNA
 * Step 1:** The two strands (sides) of the DNA are uncoiled as the hydrogen bonds between the double helix is broken. The initiation point where the splitting starts is called the "origin of replication" and the enzyme that splits the double helix goes by the name of Helicase. The structure (a y-shaped fork) created after this step is known as the "replication fork".

More detailed process of DNA replication:


 * 1) The hydrogen bonds between the bases of two strands break down. The splitting two strands happens in the chain where Adenine and thymine are bonded, because there are only two hydrogen bonds between them. The enzymes, helicase splits two strands
 * 2) Then RNA Primase binds with the parent chain. RNA Primase can attract RNA nucleotides which can bind to the DNA nucleotides because of the hydrogen bonds.
 * 3) The new strand, called lagging strand and RNA Primase inside the lagging strand adds more RNA primers.
 * 4) The DNA Pol l inside the lagging strand removes the RNA Primers. Due to the action of DNA polymerase and DNA Ligase, the gaps which is created because of removed RNA Primers are closed. Moreover it keeps adding more phosphate on the backbone (Steps of DNA Replication).



Copy the diagram in the middle of page 191, showing how DNA replicates.


Another diagram that clearly shows the process of DNA replication:

Find a good set of images or YouTube Video on DNA Replication and embed it here.
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Another great video about DNA replication:
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