# Nucleic Acids 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. ## Nomenclature - In **1920**, its chemical nature was determined to be acidic. - The name was changed from *nuclein* to **nucleic acid**. ## Types of Nucleic Acids - **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. ## General Structure Both DNA and RNA are linear, unbranched polymers. The monomers (building blocks) of nucleic acids are called **nucleotides**. ## Chemical Structure of Nucleic Acids ### Composition of a Nucleotide Each nucleotide, the monomer of a nucleic acid, is composed of three distinct parts: 1. A **pentose sugar** (a 5-carbon sugar). 2. A **phosphate group** (derived from phosphoric acid). 3. A **nitrogenous base** (a nitrogen-containing ring structure). | 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. | ### Formation of a Nucleotide The assembly of a nucleotide occurs in specific steps: 1. **Nucleoside Formation:** A nitrogenous base links to the **1' carbon** of the pentose sugar. - *Formula:* Pentose Sugar + Nitrogenous Base = **Nucleoside** 2. **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 Nitrogenous bases are divided into two main categories: 1. **Purines:** Double-ring structures (Adenine and Guanine). 2. **Pyrimidines:** Single-ring structures (Cytosine, Thymine, and Uracil).