Exon

Your body has a tiny plan.

It is like a long string. Some parts are kept. These parts are the exons.

They are the parts used to make things. Other parts are cut out. These cut parts are called introns. The exons are joined together. This helps make the final plan. Exons can be very long. Some are very short too. They work together to build you.

Inside your cells, genes hold important plans. These plans are made of different parts. Some parts are kept to make a final plan. We call these parts exons.

Other parts are cut out. These are called introns. A set of steps called RNA splicing removes the introns. Then, the cell joins the exons together. This makes a mature RNA.

Exons come in many sizes. Some are very long. Others are very short. In humans, one exon is 11,555 base pairs long. Some are only 2 base pairs long.

Exons do more than just make proteins. They also make non-coding RNA. This is RNA that does not make protein. Because exons are small, scientists can study them easily. They can study the whole exome. The exome is the set of all exons. Studying the exome is cheaper than studying the whole genome. This helps doctors with precision medicine. This is a way to give better care to people.

Inside your cells, genes hold the instructions for life. These instructions are not one long, continuous string. Instead, they are made of different pieces. One type of piece is called an exon. Exons are the parts of a gene that stay in the final plan.

This final plan is called a mature RNA. The whole collection of all exons is known as the exome. Scientists study the exome to learn about health. It is a smaller part of the genome to look at. This makes it a less expensive task for doctors.

Cells use a special way it works called RNA splicing to build these plans. A gene starts as a long sequence. This sequence contains both exons and other parts called introns. The cell must remove the introns first.

Once the introns are gone, the cell joins the exons together. They are joined by a strong bond. This creates the mature RNA that the cell can actually use. Some genes use a trick called alternative splicing. This means the cell can pick different exons to make different results. This helps one gene do many different jobs.

We can thank a scientist named Walter Gilbert for the name. He was an American biochemist. In 1978, he gave us the word exon. He shortened the phrase "expressed region."

Before this, people used a different term called a cistron. Gilbert suggested that the parts that get lost should be called introns. The parts that are expressed should be called exons. His idea helped us understand how genes are organized. This work changed how we see the instructions inside living things.

Exons come in many different sizes. In the human genome, the longest exon is 11,555 base pairs long. A base pair is a tiny unit of the genetic code. Some exons are much smaller. Some are only 2 base pairs long. In a plant called Arabidopsis, a single-nucleotide exon was found. In 2002, researchers found that most genes have about 5.48 exons.

On average, an exon holds 30 to 36 amino acids. These amino acids are the building blocks for proteins.

It is helpful to think of exons like words in a sentence. Imagine a sentence with extra, random letters mixed in. To read the sentence, you must pluck out the wrong letters. The remaining letters are the words that make sense.

In this way, exons are the meaningful parts of the genetic message. They do not just make proteins. They also make non-coding RNA. This is RNA that does not turn into protein. Exons are a vital part of how all living things function.

An exon is a vital component of a gene that remains in the final, functional RNA molecule. While genes contain many different sequences, only the exons are kept after a process called RNA splicing. This term describes both the specific DNA sequence within a gene and the corresponding sequence found in RNA transcripts. The entire collection of all exons within an organism is referred to as the exome. Understanding the exome is essential for modern biology and medicine.

To understand how exons work, one must look at the process of RNA splicing. A gene begins as a long sequence of DNA that is transcribed into a precursor molecule called pre-mRNA. This precursor contains both exons and non-coding regions called introns. During splicing, the cell removes the introns from the sequence. The remaining exons are then covalently joined to one another. This step-by-step process results in the creation of a mature RNA.

Exons serve different roles depending on the type of RNA being produced. In protein-coding genes, exons include the sequences that code for amino acids. They also include untranslated regions, known as UTRs, at the 5′ and 3′ ends of the mRNA. These UTRs are important parts of the mature molecule but are not translated into proteins. Some exons may contain only a UTR, or they may contain both coding sequences and UTRs. Furthermore, exons are found in non-coding RNA, which are molecules that do not become proteins.

Cells can also use a process called alternative splicing to increase variety. In this process, different introns are removed from the same pre-mRNA. This allows the cell to join different combinations of exons together. As a result, a single gene can produce several different mature RNAs. Another interesting phenomenon is exonization. This occurs when mutations in introns actually create a brand new exon.

The concept of the exon was defined by the American biochemist Walter Gilbert in 1978. He coined the term as a shortening of the phrase "expressed region." Before this, scientists used the term cistron to describe these units. Gilbert proposed that transcription units should be viewed as alternating regions. He suggested that the parts lost during splicing be called introns. The parts that are expressed should be called exons. This change in terminology helped clarify how genetic information is organized.

Exons vary greatly in size and frequency across different life forms. In the human genome, exons are quite rare compared to other DNA. Only about 1.1% of the human genome is made of exons. In contrast, 24% consists of introns, and 75% is intergenic DNA. This difference is significant for medical technology. Whole exome sequencing is much smaller and less expensive than whole genome sequencing. This makes it a practical tool for precision medicine.

Data from 2002 shows that protein-coding genes in GenBank have an average of 5.48 exons. On average, a single exon encodes between 30 and 36 amino acids. The size of these units can also vary wildly. The longest exon in the human genome is 11,555 base pairs long. However, some exons are extremely small, measuring only 2 base pairs. In the plant Arabidopsis, scientists have even found a single-nucleotide exon.

Scientists use several experimental methods to study these sequences. One method is called exon trapping, or gene trapping. This technique uses the way introns and exons splice to find new genes. By inserting DNA into a gene, scientists can use a reporter gene to see if it is expressed. Another method involves using Morpholino antisense oligos. These molecules can block small nuclear ribonucleoprotein particles, or snRNPs, from reaching the pre-mRNA. This allows researchers to intentionally exclude specific exons during development.