DNA and RNA

DNA Structure

DNA has a double helix. Each strand is a polynucleotide. DNA molecules are really long and are coiled very tightly so a lot of genetic information can fit into a small space in the cell nucleus. 

Nucleotide structure

Each nucleotide is made from a phosphate group, a pentose sugar and nitrogenous base. The sugar is a deoxyribose sugar. Each nucleotide has the same sugar and phosphate. The base varies between - adenine, thymine, cytosine and guanine. Adenine and guanine are purines. Cytosine and thymine are pyrimidines. 

Polynucleotide strands

The nucleotides join to…