Genes+and+Copying+DNA

** How and why does a DNA copy itself? ** The **DNA** starts **replicating** when the two sides of the DNA molecule unwind and separates, somewhat like a zipper unzipping. The hydrogen bonds between the bases are broken, separating the DNA molecule into two strands/halves. The main four nitrogen bases found linking the two strands of the DNA molecule are **cytosine**, **guanine**, **thymine**, and **adenine**. The molecule separates between the paired nitrogen bases. Then, the **nitrogen bases** floating in the nucleus pair up with the base on each half of the DNA molecule, forming **hydrogen bonds** between the new base pairs. Because of the way in which the nitrogen bases pair with one another, the order of the bases in each new DNA molecule **__exactly matches__** the order in the original DNA molecule. The DNA copies itself so that the cells produced in mitosis and meiosis would have the necessary genetic code.

media type="file" key="dna-rna2.swf" width="396" height="396" align="right"
 media type="youtube" key="tJBWPuTghM0" height="346" width="462"  Obtained from: http://www.youtube.com/watch?v=tJBWPuTghM0       ** What are genes and where are genes found? **

A **gene** is a factor that controls a **trait**. Genes are found in small sections of **chromosomes**, and chromosomes are found in the **nucleus** of cells. Chromosomes carry genes from parent to offspring. Genes determine traits like a person’s gender, eye color, skin color, hair color, blood type, etc. The nucleotide sequence of each segment contains the genetic information for making some kind of protein molecule.

Genes and DNA (has very clear definitions, images, animations that help understand the structure and places where the nucleus, chromosomes, DNA, genes, etc, are found.Also has a quiz) :http://www.abpischools.org.uk/page/modules/genome/dna2.cfm?age=Age%20Range%2014-16&subject=Biology