DNA is a biological molecule that contains the instructions an organism needs to function, develop, and reproduce. It is present in all forms of life on earth and contains each organism’s genetic code.

Virtually every cell in the body contains deoxyribonucleic acid (DNA). It is the genetic code that makes each person unique. DNA carries the instructions for the development, growth, reproduction, and functioning of all life.

Differences in the genetic code are why one person has blue eyes rather than brown, why birds only have two wings, or why giraffes have long necks. Differences or mutations in the genetic code can also lead to being susceptible to certain diseases.

Not only do nearly all cells in the body contain DNA, but the DNA in a single cell would span over 6.5 feet (ft) long if unraveled and stretched end-to-end.

This article will break down the basics of DNA, what it is made of, how it works, and how it impacts health.

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In short, DNA is a long molecule that contains each person’s unique genetic code. It holds the instructions for building the proteins essential for the body’s function.

DNA instructions pass from parent to child, with roughly half of a child’s DNA originating from the father and half from the mother.

DNA is a two-stranded molecule that appears twisted, giving it a unique shape referred to as the double helix.

Each of the two strands is a long sequence of nucleotides. These are the individual units of DNA and they are made of:

  • a phosphate molecule
  • a sugar molecule called deoxyribose, containing five carbons
  • a nitrogen-containing region

There are four types of nitrogen-containing regions called bases, including:

  • adenine (A)
  • cytosine (C)
  • guanine (G)
  • thymine (T)

The order of these four bases forms the genetic code, which is the instructions for life.

The bases of the two strands of DNA are stuck together to create a ladder-like shape. Within the ladder, A sticks to T, and G sticks to C to create the “rungs.” The length of the ladder forms through the sugar and phosphate groups.

Each length of DNA that codes for a specific protein is called a gene. For instance, one gene codes for the protein insulin, the hormone that helps control levels of sugar in the blood. Humans have around 30,000 genes, although estimates vary.

It’s believed that only about 1% of DNA is made up of protein-coding genes. Scientists know less about the function of the remaining 99% of DNA but believe them to be involved in regulating transcription and translation.

Chromosome 1 is the largest and contains around 2,800 genes. The smallest is chromosome 22 with around 750 genes.

Most DNA lives in the nuclei of cells and some exist in mitochondria, which are the powerhouses of the cells.

Because humans have so much DNA and the nuclei are so small, DNA needs to be packaged incredibly neatly.

Strands of DNA loop, coil, and wrap around proteins called histones. In this coiled state, it is DNA is called chromatin.

Chromatin condenses further through a supercoiling process and packages into structures called chromosomes. These chromosomes form the familiar “X” shape.

Each chromosome contains one DNA molecule. Humans have 23 pairs of chromosomes or 46 chromosomes in total. Other species have different numbers. For example, fruit flies have 8 chromosomes, while pigeons have 80 chromosomes.

Protein creation

For genes to create a protein, there are two main steps, including:

  • Transcription: The DNA code duplicates into messenger RNA (mRNA). RNA is a copy of DNA, but it is normally single-stranded. Another difference is that RNA does not contain the base thymine (T). In RNA, uracil (U) replaces thymine (T).
  • Translation: The mRNA translates into amino acids by transfer RNA (tRNA).

mRNA provides information on a particular amino acid via three-letter sections called codons. Each codon codes for a specific amino acid or building block of a protein. For instance, the codon GUG codes for the amino acid valine.

There are 20 possible amino acids.


Telomeres are regions of repeated nucleotides at the end of chromosomes.

They protect the ends of the chromosome from being damaged or fusing with other chromosomes.

Scientists liken them to the plastic tips on shoelaces that stop them from becoming frayed.

As a person gets older, this protective region steadily becomes smaller. Each time a cell divides and DNA is replicated, the telomere becomes shorter.

In all people, DNA degrades over time, causing people to age.

Sometimes, however, a person’s DNA sequence may change randomly. This is called a mutation. Certain mutations in a person’s genetic code can lead them to develop a variety of diseases or conditions.

Alternatively, a person can inherit a gene that may cause problems with their health. Environmental factors can influence how these mutated genes manifest.

Damage to the structure of DNA can occur in various ways. This includes when:

  • the bases connect in the wrong order after replication
  • a base pair is missing
  • there is an extra base pair
  • there is a malfunction in DNA replication or recombination
  • there is exposure to environmental factors such as radiation or heavy metals
  • there is a mutation in the process of repairing damaged DNA.
  • there is a change in the number or structure of chromosomes

Diseases or health conditions can result from damage in only one gene, such as cystic fibrosis, or damage in several parts of a person’s DNA, such as cancer. Other examples include:

  • Down’s syndrome
  • autoimmune conditions
  • chronic inflammatory conditions
  • neurodegenerative diseases like Huntington’s disease

Here are a few common questions about DNA.

Who discovered DNA?

The discovery of DNA is credited to Swiss scientist Friedrich Miescher, who first isolated DNA from human pus cells in the late 1860s.

What are the different types of DNA?

There are many types of DNA, each of which varies depending on its specific structure. The most common is B-DNA, but some other types found in the genome include A-DNA, H-DNA, and Z-DNA.

What is DNA replication?

DNA replication is a process that occurs when DNA in the cells copies itself. This helps ensure that each new cell has its own complete genome during cell division.

Can genetic diseases be cured?

Doctors can only treat the symptoms of conditions caused by a genetic mutation. However, researchers are continuously working to develop gene therapy types that may help stop a disease from progressing. The U.S. Food and Drug Administration (FDA) has approved some gene therapy drugs, while others are undergoing clinical trials.

DNA is a molecule found in most cells holding each person’s unique genetic code. It is responsible for coding proteins, which are essential to the growth and development of cells.

Chromosomes are tightly coiled strands of DNA. Genes are sections of DNA that code individual proteins. DNA also carries important genetic information necessary for the survival and function of all life forms on earth.

Put another way, DNA is the master plan for life on earth and gives all living organisms their unique genetic code. When something in this plan malfunctions, diseases and health problems can occur.