Exon and Cistron Explained with Easy Definitions and Examples
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 Exon vs Cistron: Understanding the Core Differences
1. What is an exon in the context of gene structure?
An exon is a segment of a DNA or RNA molecule that contains information coding for a protein or a specific part of a protein. In eukaryotic genes, exons are the sequences that are 'expressed'. During the process of gene transcription and splicing, the non-coding intervening sequences (introns) are removed, and the exons are joined together to form the final, mature messenger RNA (mRNA) that is used for protein synthesis.
2. What is a cistron and how is it defined?
A cistron is a functional unit of DNA that is often used as a more precise, technical term for a gene. It is defined as the smallest segment of DNA that codes for a single, complete polypeptide chain (a protein or a subunit of a protein). Therefore, a cistron represents a complete set of instructions for building one specific protein.
3. What is the primary difference between an exon and a cistron?
The primary difference is one of hierarchy and completeness. A cistron refers to the entire gene sequence responsible for a single polypeptide. An exon is only a part of that cistron. Most eukaryotic cistrons (genes) are made up of multiple exons (coding regions) and introns (non-coding regions). In essence, a cistron is the whole recipe, while exons are the essential ingredient instructions within that recipe.
4. How do introns differ from exons?
Introns and exons are both parts of a gene, but they serve opposite roles in protein synthesis:
Exons (Expressed Regions): These are the coding sequences that are retained in the final mature mRNA and are translated into an amino acid sequence.
Introns (Intervening Regions): These are non-coding sequences that are removed from the primary RNA transcript through a process called splicing. They do not contribute to the final protein product.
5. How are the concepts of gene, cistron, and exon related to each other?
These terms describe genetic units at different levels. A gene is the fundamental physical and functional unit of heredity. A cistron is a functional definition of a gene that specifies a single polypeptide. An exon is a structural component within a cistron. The relationship can be visualized as: a cistron (gene) is composed of one or more exons, which may be separated by introns. For most purposes in the CBSE syllabus, 'gene' and 'cistron' can be considered synonymous.
6. What is the importance of distinguishing between monocistronic and polycistronic mRNA?
The distinction is crucial for understanding gene regulation in different organisms.
Monocistronic mRNA is characteristic of eukaryotes. Each mRNA molecule carries the genetic information to translate only one protein, allowing for complex and independent regulation of each gene.
Polycistronic mRNA is found in prokaryotes. A single mRNA molecule contains the code for multiple, often functionally related, proteins. This allows the cell to efficiently synthesise a group of proteins needed for a specific metabolic pathway from a single transcript.
7. Are all exons necessarily coding for proteins? Explain this concept.
No, this is a common misconception. While most exons are coding sequences, some exons form the Untranslated Regions (UTRs) at the 5' and 3' ends of the mature mRNA. These UTRs are transcribed and retained after splicing (making them exons by definition) but are not translated into amino acids. They play critical roles in regulating mRNA stability, localization, and the efficiency of translation.
