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DNA, or deoxyribonucleic acid, is the molecule that carries the genetic instructions for life. It is the blueprint that determines the characteristics of all living organisms, from the simplest bacteria to complex human beings.

What is DNA?

DNA (deoxyribonucleic acid) is a long molecule that contains the genetic code used in the development and functioning of all known living organisms and many viruses. It is composed of two strands that coil around each other to form a double helix. The information encoded in DNA is used to produce proteins, which perform a vast array of functions within living cells.

Structure of DNA


DNA is made up of smaller units called nucleotides. Each nucleotide consists of three components:

  1. Phosphate group: a phosphorus atom bonded to four oxygen atoms.
  2. Deoxyribose sugar: a five-carbon sugar molecule.
  3. Nitrogenous base: one of four types – adenine (A), thymine (T), cytosine (C), or guanine (G).

Double helix

The structure of DNA is a double helix, resembling a twisted ladder. The sugar and phosphate groups form the backbone of the DNA strands, while the nitrogenous bases pair up to form the rungs of the ladder. The bases pair specifically: adenine pairs with thymine, and cytosine pairs with guanine.

Base pairing

Base pairing is the specific hydrogen bonding between adenine and thymine (A-T) and between cytosine and guanine (C-G). This complementary pairing ensures accurate replication of DNA during cell division.

Functions of DNA

Genetic information storage

DNA stores the genetic instructions needed for the development, functioning, growth, and reproduction of all living organisms. These instructions are encoded in the sequence of the nitrogenous bases.

Protein synthesis

DNA directs the synthesis of proteins through two main processes:

  1. Transcription: the process by which a segment of DNA is copied into messenger RNA (mRNA) by the enzyme RNA polymerase.
  2. Translation: the process by which the mRNA sequence is decoded by a ribosome to produce a specific protein.


DNA is responsible for heredity, the passing of genetic information from parents to offspring. During reproduction, DNA is replicated and passed on to the next generation, ensuring the continuity of genetic information.

DNA replication

DNA replication is the process by which a DNA molecule makes a copy of itself. This is essential for cell division and is a highly accurate process involving several key enzymes:

  1. Helicase: unwinds the double helix.
  2. DNA polymerase: adds nucleotides to the growing DNA strand.
  3. Ligase: seals the gaps between the newly synthesized DNA fragments.

Genetic variation

Genetic variation refers to the differences in DNA sequences among individuals. These variations can occur through mutations, recombination during sexual reproduction, and gene flow between populations. Genetic variation is crucial for evolution and adaptation.


Mutations are changes in the DNA sequence that can occur naturally or due to environmental factors. They can be:

  • Point mutations: a change in a single nucleotide.
  • Insertions/Deletions: addition or loss of nucleotide sequences.
  • Chromosomal alterations: Changes in the structure or number of entire chromosomes.

DNA and modern science

The Human Genome Project

The Human Genome Project was an international research effort to map and understand all the genes of the human genome. Completed in 2003, it has provided invaluable insights into human biology and has paved the way for advances in personalized medicine.

DNA sequencing

DNA sequencing is the process of determining the exact order of nucleotides within a DNA molecule. Modern sequencing technologies have revolutionized biological research, allowing for rapid and accurate sequencing of entire genomes.

Genetic engineering

Genetic engineering involves modifying an organism’s DNA to achieve desired traits. Techniques like CRISPR-Cas9 allow scientists to edit genes with high precision, leading to advances in medicine, agriculture, and biotechnology.

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