Deoxyribonucleic Acid (DNA)

The modern understanding of DNA has developed significantly over time, starting with the discovery of nucleic acid. In 1869, Friedrich Miescher conducted experiments using white blood cells, which he obtained from pus collected on bandages at a local hospital. He used a salt solution to wash the pus off the bandages and then added a weak alkaline solution to the cells. This caused the cells to break open (lyse) and release their nuclei, which separated from the rest of the solution.

From these cell nuclei, Miescher extracted a unique chemical substance, which he named nuclein. He found that nuclein had a high phosphorus content and exhibited acidic properties. This led to the substance being called nucleic acid. By the early 1900s, scientists discovered that Miescher's nuclein was actually a mixture of proteins and nucleic acids. Later, it was understood that there are two types of nucleic acids:

1. DNA (deoxyribonucleic acid): Responsible for storing genetic information.
2. RNA (ribonucleic acid): It plays a crucial role in protein synthesis and other cellular processes.

This discovery laid the foundation for understanding the structure and function of DNA.

DNA is the main component of chromosomes and was discovered by Swiss biochemist Frederick Miescher in 1869 while studying white blood cells. Initially, it was thought to exist only in the nucleus of cells, so it was named nucleic acid. However, it was later found in other parts of the cell as well. DNA molecules are present in all living organisms, from viruses and bacteria to humans. They control the cell's functioning, growth, and reproduction, earning the title 'Master Molecules.'

DNA (Watson and Crick’s Model)

The structure of DNA is the same in all organisms. In 1953, Watson and Crick proposed a model of DNA's structure, describing it as two parallel strands of nucleotides coiled around each other in a double helix shape. This structure can be compared to a flexible, coiled ladder:

• The rails (sides) of the ladder are made of alternating molecules of sugar and phosphoric acid.
• The rungs (steps) of the ladder are pairs of nitrogenous bases held together by hydrogen bonds.

Each strand of DNA is made up of smaller units called nucleotides, which consist of

1. A nitrogenous base
2. A sugar molecule
3. A phosphoric acid molecule

There are four types of nitrogenous bases

• Adenine (A) and Guanine (G) are called purines (double-ringed structures)
• Cytosine (C) and Thymine (T) are called pyrimidines (single-ringed structures)

The two strands of DNA are linked by hydrogen bonds between nitrogenous bases, forming specific base pairs

• Adenine (A) always pairs with Thymine (T)
• Cytosine (C) always pairs with Guanine (G)

This unique pairing ensures the DNA molecule's stability and allows it to carry genetic information. The alternating sugar and phosphoric acid molecules form the backbone, while the nitrogenous bases form the rungs, creating the ladder-like structure of the DNA molecule.

DNA Structure

1. DNA structure was first studied by Rosalind Franklin (1953); later explained by Watson and Crick, who proposed the double helix model (Nobel Prize, 1962).

2. DNA is a macromolecule made of two complementary strands twisted into a double helix.

3. Each strand is made up of nucleotides, which include phosphate, sugar (pentose), and a nitrogenous base.

4. There are four nitrogenous bases:

• Adenine (A) pairs with Thymine (T) (2 hydrogen bonds)
• Guanine (G) pairs with Cytosine (C) (3 hydrogen bonds)

5. The two strands form a ladder-like structure, with bases as rungs and sugar-phosphate as the backbone.