What is the Difference Between Exon and Cistron in Gene Structure and Function
Basic Difference Between Cistron and Exon
The nucleus of a cell is itself a universe. A vast set of information is coded in the RNA and DNA strands in the form of genes. These genes are the blueprint of an organism. The structural and functional behavior of an organism is decided by the genetic impressions. The nuclear material is formed by RNA and DNA molecules forming single and double strands respectively. The DNA strands have coding regions called as Exons. Cistrons are the smaller units present in exons that are also called genes. There is a slight difference between these two closely-related terms. Students can get easily confused with the new terms in this biology chapter. It is very important to know the exact meaning and the differences between these two terms. For this, you need to understand what is cistron and exon first and then proceed to the differences. This is where you can study the chapter first and then proceed to the tabulated difference mentioned on this concept page. The teachers of Vedantu have compiled and simplified the differences in such a way that everyone can understand them well and can script their answers in the exams.
What is the Difference Between Cistron and Exons?
As mentioned earlier, learning about DNA and its features can be very interesting but confusing too. The new terms included in the chapter can be intimidating as the meaning and concepts are very closely related. The slight differences should be highlighted so that you can understand the exact meaning of the terms. Two such terms are cistrons and exons. Let us find out the definition of both the terms and then proceed to the differences.
Cistrons are the small segments of the DNA strands. They are also called genes. These sections are responsible for triggering and coding the peptide synthesis. The coded information in these genes is used to sequence a peptide formation and result in building protein blocks. Seymour Benzer discovered what a cistron is and what are its functions. Now that you have understood the cistron meaning, let us proceed to the exons. Hence, cistrons are used to code and form polypeptide sequences during a protein synthesis process. If a DNA strand contains only one cistron, it is called monocistronic. If there is more than one cistron in the DNA strand, it is called polycistronic.
Exons are the broader coding regions present in a DNA strand. These coding sections comprise several genes or cistrons. These coding sections can also be found in the processed or mature RNA. You can say that cistrons are building blocks of exons. Every exon has information coded in it. This information is used to build protein blocks. Exons were first found by Richard Roberts. These units can either exist together or can remain separated by introns. Introns are non-coded sequences. Introns are generally removed during the formation of functional mRNA molecule. After the formation of an mRNA molecule, it is then used to translate and build protein blocks.
Why Should We Study the Differences Between Cistrons and Exons?
Now that we have studied and understood the definition of cistrons and exons, we can proceed to the differences. As we can see exons and cistrons are very closely related and are almost similar in a structural and functional way, we need to get a little deeper to understand the concept. This is where the differences between exons and cistrons tabulated properly can be used as a reference. The best way to study it first to define cistron and exon then proceed to the structural and functional differences.
The best way to achieve conceptual development and building a foundation of knowledge of this chapter is to study the differences. Comparing both the terms properly picking up the differences in a tabulated form will deliver the right format to understand and remember. It will become a lot easier to segregate both the terms structurally and functionally. In fact, the experienced teachers of Vedantu suggest how studying the difference can help you remember the main points of a term’s definition. It can be very useful when you are studying new chapters of biology in the higher classes. Once the concept is properly inculcated, you can proceed to the more advanced chapters and learn better. Learning the differences also helps you to revise the concept of cistrons and exons. You can prepare well and answer the questions easily.
FAQs on Difference Between Exon and Cistron in Genetics
1. What is the difference between exon and cistron?
The main difference between an exon and a cistron is that an exon is a coding segment of a gene that remains in mature RNA after splicing, while a cistron is a functional unit of DNA that codes for a single polypeptide.
- Exon: Part of a gene transcribed into RNA and retained after RNA processing.
- Cistron: DNA sequence that encodes one complete polypeptide chain.
- Exons are structural parts of genes; cistrons define functional gene units.
2. What is an exon in molecular biology?
An exon is a segment of a gene that is transcribed and retained in the final mature mRNA after RNA splicing.
- Exons contain coding sequences for proteins.
- They remain after introns are removed.
- Present in both eukaryotic protein-coding genes and some non-coding RNAs.
3. What is a cistron?
A cistron is a segment of DNA that codes for a single polypeptide chain and represents a functional gene unit.
- Term derived from the cis-trans test.
- In prokaryotes, one mRNA may contain multiple cistrons (polycistronic).
- Each cistron produces one specific protein product.
4. Are exon and cistron the same?
No, an exon and a cistron are not the same because an exon is a structural part of a gene, while a cistron is a functional unit encoding a complete polypeptide.
- A gene may contain multiple exons.
- A cistron corresponds to one functional protein-coding sequence.
- Exons together may form one cistron in many eukaryotic genes.
5. How are exons and introns related?
Exons and introns are parts of a gene where exons code for proteins and introns are non-coding sequences removed during RNA processing.
- Both are transcribed into pre-mRNA.
- Introns are removed by RNA splicing.
- Exons join together to form mature mRNA.
6. How does a cistron differ in prokaryotes and eukaryotes?
A cistron in prokaryotes often exists in polycistronic mRNA, while in eukaryotes most mRNA molecules are monocistronic.
- Prokaryotes: One mRNA may contain multiple cistrons (e.g., operon system).
- Eukaryotes: Typically one cistron per mRNA.
- This difference affects gene regulation and protein synthesis.
7. What is the function of exons?
The primary function of exons is to encode the amino acid sequence of proteins or functional RNA molecules.
- They determine the final protein structure.
- Participate in translation after mRNA formation.
- Can undergo alternative splicing to produce protein variants.
8. Can a gene have multiple exons but only one cistron?
Yes, a gene can contain multiple exons but still represent a single cistron if they collectively encode one polypeptide.
- Common in eukaryotic genes.
- Exons are joined after splicing.
- The combined coding sequence forms one functional protein product.
9. What is an example of a cistron?
An example of a cistron is the lacZ gene in the lac operon of Escherichia coli, which codes for the enzyme β-galactosidase.
- Part of a polycistronic operon.
- Produces one specific polypeptide.
- Demonstrates the functional gene concept.
10. Why is understanding exon and cistron important in genetics?
Understanding exons and cistrons is important because they explain gene structure and functional gene expression.
- Helps in studying genetic mutations affecting coding regions.
- Essential for understanding protein synthesis.
- Important in biotechnology, gene therapy, and molecular genetics research.
