Tour of the DNA A set of five nitrogenous bases is used in the construction of nucleotides, which in turn build up the nucleic acids like DNA. These bases are crucially important because the sequencing of them in DNA and RNA is the way information is stored. Each base is linked to another specific base. Adenine and Thymine are connected to each other through hydrogen bonds, as well as Guanine and Cytosine. These bases are broken into two separate groups, purines and pyrimidines. Adenine and Guanine are purines which means they consist of two nitrogen rings, while the pyrimidines Cytosine and Thymine consist of only one nitrogen ring. These hydrogen bonds are rather weak bond which allows for replication which we will get to later on in our tour. Each base is connected to sugar and phosphate groups making nucleotides. The sugar, ribose, has five possible carbon ends, and on these bonds is the base and phosphate group. The phosphate group is connected to the 5’ end or the fifth carbon of the ribose sugar and the first carbon is where the base and the sugar are connected. The free 3’ end is where the other phosphate groups can attach to make a chain of sugar and phosphates, the backbone of the double helix structure of DNA. The DNA consists of two of these strands of continuous nucleotides which are connected by the bases pairs along the middle of the double helix. The double helix is basically the shape of a ladder twisted round as if someone were at the top and bottom of this ladder twisting in opposite directions. Since each side consists of a 5’ and 3’ end going in opposite directions, we call the structure an antiparallel as the sides are not uniformly parallel to each other but are actually flipped and connected .The sugar phosphate back bone of the double helix is such a rigid structure due to the bonds that hold the sugar and phosphate. They are held together via covalent bonds which are extremely strong bonds in comparison to the hydrogen bonds that hold the bases together. On our next stop we will observe how our DNA replicates

DNA replication is the process of producing two identical copies from one original DNA molecule. The first step in this process is to break the hydrogen bonds between the bases. The bonds between the sugars and phosphates are not broken due to the covalent bonds. An enzyme called helicase unzips the double helix breaking the hydrogen bonds and creating two separate strands. There are two different kinds of strands, due to the fact that one strand goes from the 5’ to the 3’ end and the other 3’ to 5’. The DNA polymerase, the next protein that adds bases to the separate strands of DNA, can only go from he 5’ to the 3’ end so that strand is called the leading strand as it is replicated in a continuous motion. The other strand, the lagging strand, is given this name because the DNA polymerase has to make small fragments, Okazaki fragments, as it cannot travel from 3’ to 5’. Each fragment is then connected by an enzyme called ligase. We call this replication semi-conservative because each new strand retains one strand of the old DNA and a new one from the enzymes in the process. Next stop is DNA transcription

DNA Transcription is the process of making a single strand of RNA from double stranded DNA. In the first step of Transcription, RNA polymerase binds to the DNA at the promoter region to start the synthesis of RNA. Next, free RNA nucleotides bond through hydrogen bonding to DNA templates but the Thymine is replaced with a base called Uracil, which is unique to RNA. In the final step RNA polymerase reaches the termination point and releases the new RNA strand. Before leaving the nucleus the RNA strand is given codons from DNA which are the codes for the genes we express and don’t express. The exons, or expressed genes, and the introns, the unexpressed genes, are transferred from the DNA to