What is DNA?
Deoxyribonucleic acid (DNA) is the molecule that carries the genetic instructions used in the growth, development, functioning, and reproduction of all known living organisms.
DNA is composed of two long strands that coil around each other to form a double helix. Each strand is made of four chemical building blocks called nucleotides: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).
The sequence of these bases determines the genetic information, much like how letters of the alphabet form words and sentences.
The Structure of DNA
Double Helix Architecture
The DNA double helix consists of two anti-parallel strands that twist around each other. Each strand has:
- A sugar-phosphate backbone forming the structural framework
- Nitrogenous bases (A, T, C, G) projecting inward
- Hydrogen bonds between complementary base pairs (A-T and C-G)
Base Pairing Rules
The bases pair specifically according to Chargaff's rules:
Adenine always pairs with Thymine (2 hydrogen bonds)
Cytosine always pairs with Guanine (3 hydrogen bonds)
The Genetic Code
From DNA to Proteins
The genetic code is the set of rules by which information encoded in DNA is translated into proteins:
Transcription
DNA is transcribed into messenger RNA (mRNA) in the cell nucleus. RNA uses Uracil (U) instead of Thymine (T).
Translation
mRNA is translated into proteins by ribosomes. Each set of three nucleotides (codon) specifies an amino acid.
Protein Folding
The chain of amino acids folds into a functional protein that performs biological functions.
Codon Table
The genetic code is read in triplets called codons. Here are some examples:
Key Properties of the Genetic Code
- Universal: Nearly all organisms use the same code
- Redundant: Most amino acids are encoded by multiple codons
- Unambiguous: Each codon specifies only one amino acid
- Non-overlapping: Codons are read sequentially without overlap
DNA Replication
The Semi-Conservative Model
When cells divide, DNA must be accurately copied. The process involves:
Unwinding
Helicase enzymes unwind and separate the DNA strands
Priming
RNA primers are added to start replication
Elongation
DNA polymerase adds complementary nucleotides
Each new DNA molecule consists of one original strand and one newly synthesized strand (semi-conservative replication).
Proofreading and Repair
DNA polymerase has proofreading ability (3'→5' exonuclease activity) that corrects most errors, maintaining an error rate of about 1 in 10 billion nucleotides.
Interactive DNA Explorer
Build a DNA Strand
Select bases to create a short DNA sequence:
Your DNA Sequence:
Complementary DNA Strand:
Translate to Protein
Enter an RNA sequence (e.g., AUGUUUGCU) to translate: