What is the structure and function of DNA?

 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)