Textbook - BIOLOGICAL CHEMISTRY - Gubsky Yu.I. - 2000

Chapter I. BIOMOLECULES AND CELLULAR STRUCTURES

CHAPTER 3. NUCLEIC ACIDS. NUCLEOTIDES

3.2. NUCLEIC ACIDS: STRUCTURE AND PROPERTIES

Class="center">Primary Structure of Nucleic Acids

As already noted, all classes of Nucleic Acids (DNA and RNA) are high-molecular-weight compounds, The basis of whose Primary Structure is a polynucleotide chain built from monomeric units—NUCLEOTIDES.

Individual nucleotides are linked together into a polynucleotide chain via phosphodiester bonds formed between the 3'- and 5'-hydroxyl groups of the pentoses (riboses or deoxyriboses) of adjacent nucleotides.

In schematic representations of DNA and RNA polynucleotide chains, pentoses are denoted by vertical lines, and 3'-, 5'-phosphodiester bonds by inclined lines with the letter P (or ф) in the middle.

This same chain can be represented using the following abbreviated notation system:

pApUpGpCpApTpU

Differences in the Introduction/19.html">Primary structure of DNA and RNA:

1. DNA nucleotides contain the sugar 2'-deoxyribose instead of the ribose found in RNA nucleotides.

2. DNA and RNA nucleotides differ in their composition of pyrimidine bases:

- DNA contains the pyrimidine thymine (5-methyluracil);

- RNA contains the pyrimidine uracil (instead of thymine).

3. The primary structure of DNA and RNA differs in the presence of certain minor nucleotides.

4. Specific classes of DNA and RNA possess characteristic nucleotide sequences that determine their biological Functions.

Table 3.2. Features of the primary structure of DNA and RNA

Polarity of polynucleotides

In a DNA or RNA polynucleotide chain, two ends are distinguished: the 5'-end, which contains a free (unlinked to the next nucleotide) 5'-hydroxyl group of the pentose, and the 3'-end, which contains a free (unlinked to a nucleotide) 3'-hydroxyl group of the pentose. In natural nucleic acids, the 5'-end (the 5'-hydroxyl of the terminal ribose or deoxyribose) is typically phosphorylated, while the 3'-end contains a free OH group. It is generally accepted that such a nucleic acid is polar and has a chain direction of