photo.jpg

# Molecular Biology - Theoretical ## Pyrimidines ### Figure 5 - Nitrogenous bases within DNA are categorized into two-ringed purines adenine and guanine and the single-ringed pyrimidines cytosine and thymine. - Thymine is unique to DNA. ### Individual Nucleoside Triphosphates - Combine with each...

# Molecular Biology - Theoretical ## Pyrimidines ### Figure 5 - Nitrogenous bases within DNA are categorized into two-ringed purines adenine and guanine and the single-ringed pyrimidines cytosine and thymine. - Thymine is unique to DNA. ### Individual Nucleoside Triphosphates - Combine with each other by covalent bonds known as 5'-3' *phosphodiester* bonds - Phosphate group attached to the 5' carbon of the sugar of one nucleotide bonds to the hydroxyl group of the 3' carbon of the sugar of the next nucleotide. - Phosphodiester bonding forms the *sugar-phosphate* backbone, the alternating sugar-phosphate structure composing the framework of a nucleic acid strand (Figure 6). ### Polymerization Process - Deoxynucleotide triphosphates (dNTP) are used. - To construct the *sugar-phosphate backbone*, the two terminal phosphates are released from the dNTP as a *pyrophosphate*. - Resulting strand of nucleic acid has a free phosphate group at the 5' carbon end and a free hydroxyl group at the 3' carbon end. - The two unused phosphate groups from the nucleotide triphosphate are released as *pyrophosphate* during phosphodiester bond formation. - Pyrophosphate is subsequently hydrolyzed, releasing the energy used to drive nucleotide polymerization.