The key difference between replication and transcription is that replication is the process that produces two identical copies of DNA from an original DNA molecule while transcription is the first step of gene expression that produces mRNA molecule from a DNA template.
Cells divide and increase in number in order to grow and develop. Furthermore, the production of reproductive cells is necessary to maintain their generations. The cell cycle is a series of events related to the production of new daughter cells from a cell. During the cell cycle, two processes known as replication and transcription are utmost important. It is because replication facilitates the transmission of genetic information to the next generation while the transcription facilitates the production of proteins that are necessary for the nuclear division. Both replication and transcription occur at the interphase of the cell cycle but, at different sub-phases.
CONTENTS
1. Overview and Key Difference
2. What is Replication
3. What is Transcription
4. Similarities Between Replication and Transcription
5. Side by Side Comparison – Replication vs Transcription in Tabular Form
6. Summary
What is Replication?
DNA replication is a process that produces two identical copies of DNA from an original DNA molecule. It is a complex process that takes place during the S (synthesis) phase of the cell cycle. Thus, DNA replication facilitates the inheritance of genetic information stored in the parental DNA through the progeny. Also, during the replication process, both strands of DNA serve as templates. Hence, it occurs in a semi-conservative manner.
Furthermore, a group of enzymes called DNA polymerases; the topoisomerase, DNA helicase, DNA primase, and DNA ligase, involve in the DNA replication process. With the assistance of a short RNA primer, DNA replication process begins. And, DNA helicase is the enzyme that separates or unwinds two DNA strands in order to use the templates for the formation of new strands. Also, DNA replication occurs bi-directionally starting from the site called replication fork.
Figure 01: DNA Replication
Since there are two strands, two new strands; leading strand and lagging strand form at the end of the replication process. Leading strand is the new DNA strand that synthesizes continuously while the lagging strand is the second new strand that synthesizes as pieces (Okazaki fragments). The addition of nucleotides by DNA polymerase occurs in the direction of 3’ to 5’. It also facilitates the proofreading activity in the same direction to eliminate mismatched pairs.
What is Transcription?
Transcription is the first step of gene expression in which the genetic information stored in the coding sequence of the gene copies into a mRNA sequence in order to produce a protein. It is an enzyme-driven process. In fact, RNA polymerase is the main enzyme that catalyzes the transcription. There are three main steps of transcription namely initiation, elongation and termination. Transcription process initiates soon after binding the RNA polymerase and transcription factors with the promoter sequence located upstream to the transcription initiation unit. This binding creates a transcription bubble at the transcription unit.
Figure 01: Transcription
Once the transcription initiation site is established, RNA polymerase catalyzes the addition of ribonucleotides in order to form the mRNA sequence. Consequently, it synthesizes the primary mRNA transcript by reading the antisense DNA strand in the direction of 3’ to 5’. This results in an RNA strand which is complementary and antiparallel to the template strand but contains the genetic code of the sense sequence. Transcription process terminates by adding a polyadenine tail when the RNA polymerase gets the termination signal. In prokaryotes, addition to the polyadenine tail, 5’end capping and exon splicing occur as post-transcriptional modifications.
What are the Similarities Between Replication and Transcription?
- Replication and transcription are complex processes.
- They are highly regulated processes that take place at the cellular level.
- Also, both replication and transcription occur during the cell cycle, and they are important for the completion of the cell cycle.
- Moreover, they are enzyme-catalyzed reactions driven in the 3’ to 5’ direction.
- Furthermore, both processes constitute three main steps; the initiation, elongation, and termination.
- Besides, DNA unwinding is an essential event in both processes.
What is the Difference Between Replication and Transcription?
Replication and transcription are two important events that take place in the cells of living organisms. Replication is the process of copying a DNA molecule and producing replicas of it. On the other hand, transcription is the first step of gene expression in which the nucleotide sequence of the coding sequence is copied into a mRNA molecule. Thus, this is the key difference between replication and transcription. In replication, both DNA strands work as templates while in transcription, only the antisense DNA sequence acts as a template. Hence, it is another difference between replication and transcription.
Furthermore, one other difference between replication and transcription is that the DNA polymerase catalyzes the replication while RNA polymerase catalyzes the transcription. Moreover, replication needs an RNA primer while transcription does not require a primer. Thus, this is also a difference between replication and transcription.
The below infographic presents more details on the difference between replication and transcription.
Summary – Replication vs Transcription
Replication and transcription are two events that occur during the cell cycle. Both processes take place in the nucleus but occur due to two different objectives. Replication occurs in order to transmit the genetic information into the next generation while the transcription occurs in order to produce proteins. In summary, the key difference between replication and transcription is the resulting molecule. Replication produces two identical copies of DNA while the transcription produces a mRNA molecule.
Reference:
1.Nature News, Nature Publishing Group. Available here
2.“Overview of Transcription.” Khan Academy, Khan Academy. Available here
Image Courtesy:
1.”13080697695″ by Genomics Education Programme (CC BY 2.0) via Flickr
2.”Simple transcription elongation1″By Forluvoft – Own work, (Public Domain) via Commons Wikimedia