What is DNA?

DNA stands for Deoxyribonucleic Acid. It is the molecule that carries the genetic instructions used in the growth, development, functioning, and reproduction of all living organisms.

DNA is found inside the nucleus of most cells, tightly packed into thread-like structures called chromosomes. Each chromosome contains one long molecule of DNA.

Structure of DNA

DNA has a double helix shape, which looks like a twisted ladder. This structure was first described by James Watson and Francis Crick in 1953.

The DNA molecule is made up of smaller units called nucleotides. Each nucleotide consists of:

• A phosphate group
• A sugar molecule (deoxyribose)
• A nitrogenous base

There are four types of nitrogenous bases in DNA:

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

These bases pair in a specific way:

• A pairs with T
• C pairs with G

This is known as complementary base pairing.

The order of these bases forms a genetic code that determines the characteristics of an organism.

Function of DNA

1. Storage of Genetic Information
   DNA carries the instructions for making all the proteins in a living organism. These instructions are passed from parent to offspring.
2. Replication
   DNA can make exact copies of itself. This is important when cells divide, so that each new cell gets an identical copy of DNA.
3. Control of Cell Activities
   DNA determines what proteins a cell makes. Proteins control most of the functions in a cell, such as enzyme activity, structure, and communication.

Where is DNA Found?

• In eukaryotic cells (like plant and animal cells), DNA is located inside the nucleus.
• In prokaryotic cells (like bacteria), DNA floats freely in the cytoplasm, as these cells do not have a nucleus.
• Small amounts of DNA are also found in mitochondria (called mitochondrial DNA) and in chloroplasts in plant cells.

Important Facts About DNA

• Humans have 46 chromosomes (23 pairs), each made of DNA.
• The complete set of DNA in an organism is called its genome.
• All cells in your body (except red blood cells) contain the same DNA.
• Differences in DNA sequences are what make individuals unique.

Understanding DNA is key to learning about heredity, variation, genetic disorders, biotechnology, and how traits are passed on from parents to offspring. DNA is often called the “blueprint of life” because it contains the instructions for building and maintaining living organisms.