2.21 Nucleic Acid | Molecular Biology | Biology 11

Nucleic acids are the polymers that form the basis of genetic material, essential for the storage and transmission of hereditary information.

Discovery

First reported in 1869 by Swiss physician Friedrich Miescher.
He isolated a new compound from the nuclei of pus cells (white blood cells).
It was not a protein, lipid, or carbohydrate, so it was named nuclein because it was found in the nucleus.

Deoxyribonucleic Acid (DNA): Found primarily in the nucleus (chromosomes) and also in mitochondria and chloroplasts.
Ribonucleic Acid (RNA): Found in the nucleolus, ribosomes, and cytoplasm.

Both DNA and RNA are linear, unbranched polymers. The monomers (building blocks) of nucleic acids are called nucleotides.

Each nucleotide, the monomer of a nucleic acid, is composed of three distinct parts:

Component	Description	Role/Property
Pentose Sugar	In DNA: Deoxyribose. In RNA: Ribose.	Forms the backbone of the nucleic acid polymer.
Phosphate Group	Derived from phosphoric acid.	Provides the acidic properties of nucleic acids. Links sugars together to form the backbone.
Nitrogenous Base	A nitrogen-containing ring structure.	Termed a "base" because the unshared pair of electrons on nitrogen atoms can accept a proton. Carries the genetic code.

The assembly of a nucleotide occurs in specific steps:

Nucleoside Formation: A nitrogenous base links to the 1' carbon of the pentose sugar.
- Formula: Pentose Sugar + Nitrogenous Base = Nucleoside
Nucleotide Formation: A phosphate group (phosphoric acid) links to the 5' carbon of the pentose sugar in a nucleoside.
- Formula: Nucleoside + Phosphate Group = Nucleotide

Classification by Phosphate Groups: Nucleotides can be classified by the number of phosphate groups attached:
- Nucleoside Monophosphate (NMP): One phosphate group.
- Nucleoside Diphosphate (NDP): Two phosphate groups.
- Nucleoside Triphosphate (NTP): Three phosphate groups (e.g., ATP - Adenosine Triphosphate).

The polymerization of nucleotides into nucleic acids occurs through phosphodiester bonds.

Nitrogenous bases are divided into two main categories:

Each nucleotide, the monomer of a nucleic acid, is composed of three distinct parts:

A pentose sugar (a 5-carbon sugar).

A phosphate group (derived from phosphoric acid).

A nitrogenous base (a nitrogen-containing ring structure).

Figure 2.34: General structure of a nucleotide, showing the three main components.

Component	Description	Role/Property
Pentose Sugar	In DNA: Deoxyribose. In RNA: Ribose.	Forms the backbone of the nucleic acid polymer.
Phosphate Group	Derived from phosphoric acid.	Provides the acidic properties of nucleic acids. Links sugars together to form the backbone.
Nitrogenous Base	A nitrogen-containing ring structure.	Termed a "base" because the unshared pair of electrons on nitrogen atoms can accept a proton. Carries the genetic code.

The assembly of a nucleotide occurs in specific steps:

Nucleoside Formation: A nitrogenous base links to the 1' carbon of the pentose sugar.

Nucleotide Formation: A phosphate group (phosphoric acid) links to the 5' carbon of the pentose sugar in a nucleoside.

Classification by Phosphate Groups: Nucleotides can be classified by the number of phosphate groups attached:

Nucleoside Monophosphate (NMP): One phosphate group.
Nucleoside Diphosphate (NDP): Two phosphate groups.
Nucleoside Triphosphate (NTP): Three phosphate groups (e.g., ATP - Adenosine Triphosphate).

The polymerization of nucleotides into nucleic acids occurs through phosphodiester bonds.