The sympathetic nervous systemâs fight-or-flight response is your built-in mechanism for safely escaping a life-threatening emergency, such as a lion lurking behind a bush.
The basic building block of DNA is called a NUCLEOTIDE. A nucleotide is made up of one sugar molecule, one phosphate molecule and one of the four bases. Here is the structural formula for the four nucleotides of DNA. Note that the purine bases (adenine and guanine) have a double ring structure while the pyrimidine bases (thymine and cytosine) have only a single ring.
The phosphate group is bonded to the 5 carbon of the sugar (see Figure 2), and when nucleotides are joined to form RNA or DNA, the phosphate of one nucleotide is joined to the sugar of the next nucleotide at its 3 carbon, to form the sugar-phosphate backbone of the nucleic acid.