What is DNA?

If you’ve watched a few sci-fi movies or TV shows, you would have seen an image of this helix-shaped molecule made up of multiple tiny bits.

This is what scientists call DNA, or deoxyribonucleic acid.

It is the hereditary molecule found in humans and almost all other organisms. Almost all cells in the human body contain the same DNA. Most of the DNA is packaged in the cell nucleus (the cell nucleus stores nuclear DNA). Only a small amount of DNA is found in the mitochondria* within human cells. This type of DNA we call mitochondrial DNA or mtDNA.

*Mitochondria are structures within cells that are are called the “powerhouse” of the cell, becuase they convert the energy from food into a form of energy that the cells are able to use.

What is DNA made up of?

There are four main chemical bases that make up DNA: adenine (A), guanine (G), cytosine (C), and thymine (T).

Humans contain about 3 billion bases. More than 99% of these bases have been found to be the same in all humans.

The order of the bases determine what proteins are going to be built, and this is important for the maintenance of a healthy organism.

The easiest way to understand the importance of the order of the bases is to compare it to the alphabet. Letters in the alphabet appear in a specific order to be able to form words and sentences that are understandable to us.

These DNA bases have a specific way of pairing up with each other: At with T, and C with G. These pairing-up forms units called base pairs.

Each base is also attached to a sugar molecule as well as a phosphate molecule. The base, sugar and phosphate are collectively called a nucleotide.


These nucleotides are arranged in two long strand that form a double helix. The double helix looks like a ladder that is spiraling. The steps of the ladder are made up of base pairs. The outside vertical sidepieces of the ladder is made up of the sugar and phosphate molecules.

There are different structures of DNA called A-DNA, B-DNA and Z-DNA. If you want to learn more about these, you can click on the picture below which will take you to the HHMI website where these structures were first observed.

Click on the image to learn more of DNA (Image from https://www.hhmi.org/)

Possibly the most important property of DNA is that it can replicate, which means that it can be made into identical copies of itself. Each strand of DNA serves as a blueprint/pattern for making more copies of DNA and placing the bases in the identical pattern as the original strand.

DNA replication is critical when cells divide because each new cell needs to have an exact copy of DNA that is found in the previous/older cell. This happens during cell division.

The next topic that will be discussed is “What is a gene?”. This will give you a better idea of where DNA fits into the cell and why it is so important for the correct order of bases to be replicated during cell division.

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