Genetics SitesHuman Genome Project
DNA Learning Center
Dictionary of Biological
Terms. 10th Ed. John Wiley & Sons.
DNA & RNA Structure
DNA and RNA are a macromolecule made from three types of organic molecules: sugars, organic phosphate, and nitrogen bases. The sugars and organic phosphates compose the backbone of DNA and RNA. They differ in the type of sugar that they have. DNA has the sugar deoxyribose, while RNA has the sugar ribose. Both DNA and RNA contains the purine nitrogen bases adenine and guanine, and they contain the pyrimidine nitrogen base cytosine. DNA and RNA also differ in the last pyrimidine nitrogen base that they contain. DNA has thymine, and RNA contains uracil.
As it was mentioned above, the sugars and organic phosphates form the backbone of the molecule. The macromolecule can be broken down into subunits called nucleotides. A nucleotide is formed by an organic phosphate attached to the sugar, and a nitrogen base which is also attached to the sugar.
The last differences between DNA and RNA is size and the number of subunits. RNA is a relatively small macromolecule, made from a single backbone of organic phosphate and ribose, and the nitrogen bases adenine, guanine, cytosine, and uracil. RNA forms a single strand.
In contrast, DNA is much longer, and DNA is formed from a two backbones of organic phosphate and deoxyribose, forming a double strand that wraps around itself like a spiral staircase. This wrapping forms the double helix shape of DNA, where the nitrogen bases form the steps, and the organic phosphates and deoxyribose forms the runners. In DNA, the bases are attached through hydrogen bonding. The base thymine always binds with adenine, while the base cytosine always binds with guanine.
Asking the question, where are the genes, the answer becomes simple when you looking for what changes in the DNA molecule. The entire backbone is made from the same two molecules, deoxyribose and organic phosphate, attached to each other in the same order. But there are four nitrogen bases, which order changes. The genes are the sequence of the bases. (To read more about how the bases translate into traits, see protein synthesis).
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