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.
Ribose is the sugar component of nucleotides. One of the main chemical differences between DNA and RNA is that in RNA, the sugar is ribose, but in DNA, the sugar is deoxy ribose, in which an oxygen has been removed. The connection that forms between nucleotides is between the sugar of the first nucleotide and the phosphate group of the second. 2  Each connection between nucleotides is a covalent bond, so the nucleic acids have a covalently attached sugar-phosphate backbone.