(c)+DNA+replication



**__What is DNA Replication? __** In order for one organism to pass on characteristics to its offspring, DNA in the chromosomes must be copied or "replicated". This process is called the DNA Replication, which is the basis of all biological inheritance, and is the fundamental process occurring in all living organisms to copy their DNA. The process of DNA replication consists of opening a Double Helix and separating the two strands to produce two identical DNA Double Helixes from one DNA molecule. The coded sequence on one chain of the Double Helix automatically determines the coded sequence on the other chain, which ensures the accurate replication. The steps of DNA replication is outlined below :


 * The DNA strand is unzipped and the two sides break apart from each other.
 * Nucleotides arrive from other parts of the body and bond with the half strand of DNA and since Ademine always bonds with Thymine while Guamine always bonds with Cytosine it's the same kind of nucleotide as before that bonds with any given nucleotide on the half strand.
 * The end result is two strands of DNA that look exactly the same.

__**What Happes during the Process of DNA Replication?**__

Before a cell can divide, it must duplicate, or replicate, all of its DNA. In eukaryotes, this process occurs during the S phase of the cell cycle, which is also called the DNA Synthesis phase. During this phase, each chromosone replicates exactly once to form a pair of physically linked sister chromatids. In animal cells, a pair of centrioles is also duplicated during the S phase.

**Step 1:** The DNA replication process begins with the 'unzipping' of the parent molecule. The two strands are separated like the two sides of a zipper by breaking the weak hydrogen bonds between the two paired bases.

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(The Video of DNA "unzipping")

IMAGE OF DNA 'UNZIPPING'

 **Step 2:** The 2 strands of DNA molecule consist of complementary base pairs. Once they are exposed, the sequence of bases on each of the seperated strands gathers and supplies the information needed to produce and create its partner. They are like templates that aid and guide the insertion of a complementary set of strands that is being synthesized.

**Step 3:** Each template and its new complement are assembled. The enzyme DNA polymerase moves along the exposed DNA strand, and bonds new nucleotides into a new DNA strand that is complementary to the template. Each cell has to contain a family of more than 30 enzymes to ensure the most precise replication of DNA.
 * Each nucleotide is bonded to the free 3-carbon carbon on the pentose as the second and third phosphates are removed together as a molecule of pyrophosphate


 * Adenine always pairs with Thymine, and Guanine always pairs with Cytosine

**Step 4:** When the process is finished, new 2 DNA double helices are formed, exactly identical to each other and to the parent molecule (which is why the process is called DNA //replicating//)

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("How DNA Copies Itself")

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﻿ (DNA Replication)

Step 1: The two strands (sides) of the DNA



Each strand acts as a template for making another strand using a supply of nucleotides. The leading strand is synthesized in the same direciton as the movement of the replication fork. The replication fork moves along it in the 5 to 3 direction. The lagging strand is synthesized in the opposted direction. The lagging strand cannot be replicated continuosly. The replication fork moves along it in the 3 to 5 direction.

<span style="background: white; color: #333333; font-family: 'Arial','sans-serif'; font-size: 10.5pt; line-height: normal; margin: 0in 0in 0pt;">__Step 2:__ The process results in two separate strands.

<span style="background: white; color: #333333; font-family: 'Arial','sans-serif'; font-size: 10.5pt; line-height: normal; margin: 0in 0in 0pt;">How DNA replicates <span style="background: white; color: #333333; font-family: 'Arial','sans-serif'; font-size: 10.5pt; line-height: normal; margin: 0in 0in 0pt;">

Custer, Nancy V. "DNA Replication." //Contexo//. 2009. Web. 28 Apr. 2011. <http://www.contexo.info/DNA_Basics/DNA%20Replication.htm>.
 * <span style="background: white; color: #800080; font-family: 'Arial','sans-serif'; font-size: 130%; line-height: normal; margin: 0in 0in 0pt;">Sources : **

Pickering, W. R. "11.2 DNA, Proteins and the Characteristics of Organisms." //Complete Biology//. Oxford: Oxford UP, 2000. 190-91. Print.