DNA (Deoxyribonucleic Acid) is the molecule of life—it carries the genetic instructions used in the growth, development, functioning, and reproduction of all known living organisms and many viruses.

🧬 Structure of DNA

  • DNA has a double helix structure—imagine a twisted ladder.

🧱 Key Components:

  • Nucleotides – The building blocks of DNA, each made of:
  • Phosphate group
  • Deoxyribose sugar (a 5-carbon sugar)
  • Nitrogenous base (A, T, C, or G)

Nitrogenous Bases – There are four:

  • Adenine (A)
  • Thymine (T)
  • Cytosine (C)
  • Guanine (G)

🔗 Base Pairing Rules:

  • A pairs with T
  • C pairs with G
  • (These are held together by hydrogen bonds)

Backbone:

  • The sides of the ladder are made of sugar-phosphate chains, connected by phosphodiester bonds.

Double Helix:

  • Two strands run in opposite directions (antiparallel).
  • Discovered by Watson and Crick (1953), with crucial X-ray data from Rosalind Franklin.

🎯 Function of DNA

  • DNA stores and transmits genetic information. Its main functions are:

1. Genetic Code

DNA contains genes, which are sequences of nucleotides that code for proteins.

A gene is essentially a "recipe" for making a specific protein.

2. Protein Synthesis

  • DNA → RNA → Protein
  • (This is called the Central Dogma of Molecular Biology)

Steps:

  • Transcription: DNA is used to make messenger RNA (mRNA) in the nucleus.
  • Translation: mRNA is read by ribosomes to assemble amino acids into a protein.

3. Replication

  • DNA can copy itself during cell division.
  • Each strand serves as a template for a new strand, ensuring that each new cell gets a complete copy of genetic material.

4. Heredity

  • DNA is passed from parents to offspring.
  • Variations in DNA (mutations) lead to genetic diversity, which drives evolution.

🧠 Summary Table

  • Feature DNA
  • Full name Deoxyribonucleic Acid
  • Shape Double helix
  • Subunits Nucleotides (sugar, phosphate, base)
  • Bases A, T, C, G
  • Base pairing A–T, C–G
  • Location Mostly in the nucleus (in eukaryotes)
  • Function Stores genetic information; directs protein synthesis
  • Replication Semi-conservative (each new molecule has one old strand)