Genomics 101: What is non-coding DNA?

In this series, ‘Genomics 101’, we go back to basics and explore some of the most important topics in genomics. In this blog, we explain the term ‘non-coding DNA’, and the important role it plays in our genome.

First things first, what is DNA?

DNA is a molecule found in all living things. It carries the genetic information we need to survive, like an instruction manual for our body.

DNA sequences are made of a 4 different ‘bases’, which we represent using the letters A, T, C and G.

The cells in our body can read this sequence of letters, almost like reading a book, and produce all the different proteins we need to survive.

Proteins are important nutrients that allow our cells to function and repair themselves. The order of letters in the DNA sequence determines which protein is produced.

So then, what is non-coding DNA?

Non-coding DNA is the portion of our DNA that does not code for proteins.

It is also sometimes known as ‘junk DNA’ or ‘DNA dark matter’, because it took scientists a long time to understand what it was used for and whether it was important.

We still don’t know the exact purpose of non-coding DNA; however, we do know that some of it plays an important role in our biology.

What is the function of non-coding DNA?

Scientists are still studying non-coding DNA because there are lots of things we don’t know about it.

However, research has found that it plays an important role in 2 essential processes: gene expression and maintaining genome structure.

What is gene expression?

Gene expression refers to where, when, and how much of each protein is made. In other words, how our genes are expressed as proteins.

This process must be tightly controlled in every cell of our body, as proteins made in the wrong place, time, or amount can be harmful.

Non-coding DNA provides vital genetic information to regulate this process of gene expression, ensuring that proteins are being produced just as they should be.

And what about genome structure?

Our DNA is stored in tightly wound structures called chromosomes. These chromosomes sit in a part of the cell called the nucleus.

At the ends of these chromosomes is a section of repetitive DNA, called a telomere. These telomeres protect the chromosome from being degraded, almost like the plastic bits at the end of our shoelaces to stop them from fraying.

These telomere sequences are made up of non-coding DNA, and are vital to maintaining a genome with a healthy structure and function.

Where is non-coding DNA stored?

Great question! Just like the rest of our DNA, non-coding DNA is part of the genome. This means it is kept in the same place, tightly wound up in chromosomes in the nucleus of each cell.

The genome is the word we use to describe all the DNA we have, the end-to-end sequence of bases that our body needs to survive and function.

Some parts of this sequence code for proteins, and some parts do not.

In fact, it is estimated that 98.5% of our genome is non-coding, so the vast majority of our DNA does not directly code for proteins.

Can non-coding DNA affect our health?

In short, yes. Sometimes problems in non-coding DNA can lead to problems for our health.

Gene regulation and genome structure are both essential for healthy protein production.

As a result, genetic changes in non-coding DNA that alter these processes can cause problems with protein production, which can directly impact the function of our cells.

You can read more about genetic changes in a previous blog.

Can you give an example?

There are several conditions thought to be caused by non-coding DNA, with growing evidence to support its role in Parkinson’s disease, autism, and several cancers.

To give a specific example, recent research identified a non-coding gene that causes neurodevelopmental disorders, which are conditions that affect the function of the brain.

This gene, known as RNU4-2, is now known to be the most common cause of neurodevelopmental disorders, with hundreds of people across the UK, Europe and the US having received a diagnosis following this research.

Read more about this research in a previous blog.

Non-coding DNA and whole genome sequencing

Standard genetic tests mostly look at genes that code for proteins. This means that genetic changes in non-coding DNA are often not detected.

As a result, people with conditions or cancers caused by non-coding genes may not receive a genetic diagnosis through standard testing.

Unlike standard genetic tests, whole genome sequencing aims to look at the entire sequence of DNA at once.

This means it can detect genetic changes in the non-coding genome, improving our understanding of the role it plays in our health.

You can read more whole genome sequencing in a previous blog.