What is the Difference Between Cistron and Exon

Cistron and exon are both integral components of DNA and RNA. If an exon contains one cistron, it is called monocistronic, while if it contains more than a cistron, it is called polycistronic. Francis Crick proposed the theory of central dogma in the 1950s, which states that genetic information flows from DNA to RNA to protein.

The key difference between cistron and exon is their nature. Cistron is a DNA segment that has the information to produce a specific peptide sequence, while exon is a DNA segment that is a part of the coding sequence of a protein.

CONTENTS

1. Overview and Key Difference
2. What is Cistron 
3. What is Exon
4. Similarities – Cistron and Exon
5. Cistron vs Exon in Tabular Form
6. Summary – Cistron vs Exon
7. FAQ: Cistron and Exon

What is Cistron?

Cistron is a small segment of DNA strand. It is also called a gene since it is a DNA segment that guides the production of a specific peptide sequence. In other words, cistron has the information to produce a single polypeptide chain. Seymour Benzer was the first scientist to discover the cistron and its function.

A cistron was originally defined experimentally as a genetic complementation unit through a test called the cis/trans test. Moreover, the DNA segments can be monocistronic, which means having one cistron, or polycistronic, which means having multiple cistrons.

What is Exon?

Exons are the broader coding regions present in a DNA strand. It can be monocistronic or polycistronic. Every exon has information coded in it. The exon can also be found in the processed or mature RNA. Exon was discovered by Richard Roberts.

Exons can either exit together or remain separated by introns. Introns are basically non-codon regions. Introns are removed after transcription through a process called splicing in order to make a functional mRNA molecule. Furthermore, after the formation of a functional mRNA molecule, this is then used to translate and build protein molecules.

Similarities Between Cistron and Exon

1. Cistron and exon are both integral components of DNA and RNA
2. Both are two associated structures.
3. Exon may have one cistron or multiple cistrons.
4. Both are involved in making proteins through protein synthesis.

Difference Between Cistron and Exon

Definition

1. Cistron is the DNA segment that directs the synthesis of a peptide sequence.
2. Exon is the coding section of DNA that has one cistron or multiple cistrons.

Alternative Names

1. Cistrons are also known as genes.
2. Exons are also known as the coding regions or expressed sequences.

Discovered by

1. Cistrons were discovered by Seymour Benzer.
2. Exons were discovered by Richard Roberts.

Consists of

1. Cistrons consist of both coding and regulatory sequences.
2. Exons consist of coding sequences.

Function

1. Cistrons are DNA segments that code for a specific polypeptide in protein synthesis.
2. Exons are segments of DNA and RNA that contain information coding for a protein or peptide sequence.

The following table summarizes the difference between cistron and exon.

Summary – Cistron vs Exon

Cistron is a genetic unit encoding a single polypeptide discovered by Seymour Benzer in 1957 while exon is a coding region of DNA that has one cistron or several cistrons discovered by Richard Roberts in 1970s. Exons is also known as the nucleotide sequence that remains in a mature mRNA. This is the basic difference between cistron and exon.

FAQ: Cistron and Exon

1. What is the Benzer concept of cistron?

• The word cistron was first discovered by Seymour Benzer when he performed his complementation cis/trans test by putting two genes together in a cytoplasm to study their interactions. Later, it was defined as a DNA segment that guides the production of a specific peptide sequence.

2. What is an example of a cistron?

• A cistron is basically an alternative name for a gene. If a stretch of replicating DNA contains a single cistron, it is called monocistronic. Single cistron can be found in eukaryotes. If a stretch of replicating DNA contains more than one cistron, it is called polycistronic. Multiple cistrons can be found in bacteria and prokaryotes.

3. What is the main function of exon?

• An exon in a DNA strand is the coding sequence. It will be used to translate the sequences into amino acids. Later, it will be folded into functional proteins.

4. What is the role of the exon in a gene?

• Exons are coding sections of a DNA encoding it or RNA transcript. They are translated into protein. Exons can be separated by intervening sections of DNA that do not code for proteins.

5. How do exons work?

• Exons are interspersed with introns, sometimes also called ‘junk DNA.’ The introns are cut out and discarded in the process of splicing before protein production. This leaves only the exons responsible for the production of functional protein.

Reference:

1. “Cistron.” An Overview | ScienceDirect.
2. “Exons.” Nature News, Nature Publishing Group.

Image Courtesy:

1. “Gene Intron Exon nb” By Smedlib – Own work (CC BY-SA 4.0) via Commons Wikimedia

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