Nucleotide Structure. The basic building block of DNA is the nucleotide. The nucleotide in DNA consists of a sugar (deoxyribose), one of four bases (cytosine (C), thymine (T), adenine (A), guanine (G)), and a phosphate. Cytosine and thymine are pyrimidine bases, while adenine and guanine are purine bases.
Answer: . Estuaries rank high on the list of the most heavily impacted aquatic systems on earth. This is largely attributed to accelerating population growth and development in the coastal zone and escalating use of estuarine resources.
