The key difference between post transcriptional and post translational modification is that post transcriptional modification occurs after the transcription step of the protein synthesis, while post translational modification occurs after the translation step of the protein synthesis.
Protein synthesis contains two basic mechanisms as transcription and translation. In transcription, a DNA molecule is converted into mRNA, while in translation, the mRNA molecule is converted into the final protein. After each step, modifications or processing to the newly synthesized molecule happen. They are called post transcriptional and post translational modification. These modifications are extremely important for making fully functional protein molecules in the body.
CONTENTS
1. Overview and Key Difference
2. What is Post Transcriptional Modification
3. What is Post Translational Modification
4. Similarities – Post Transcriptional and Post Translational Modification
5. Post Transcriptional vs Post Translational Modification in Tabular Form
6. Summary – Post Transcriptional vs Post Translational Modification
What is Post Transcriptional Modification?
Post transcriptional modification occurs after the transcription step of protein synthesis. In this mechanism, the newly synthesized mRNA molecule is modified before moving into the translation step of protein synthesis. Post transcriptional modification is normally common to most eukaryotic cells, in which the primary RNA molecules that are synthesized in the transcription process are chemically altered following the transcription process. This converts the primary RNA molecule into a mature mRNA molecule. After post transcriptional modifications, the mature mRNA molecule leaves the nucleus and performs a variety of different functions in the biological cell. There are many types of post transcriptional modifications.
Figure 01: Post Transcriptional Modification
One main example is the conversion of precursor mRNA molecule into mature mRNA molecule that is capable of being translated into a functional protein. This conversion involves three major chemical changes. They are the addition of a 5’ cap to a pre-mRNA molecule, the addition of a 3’ polyadenylated tail to a pre-mRNA molecule, and mRNA splicing (removing introns and joining exons). The above cap and tail facilitate the transport of mRNA to a ribosome and protect it from degradation. On the other hand, mRNA splicing helps make a specific protein molecule by using a peculiar mRNA molecule. Furthermore, post transcriptional modifications may also occur during the processing of other RNA molecules, such as tRNA and rRNA.
What is Post Translational Modification?
Post translational modification occurs after the translation step of the protein synthesis. By using this mechanism, the protein molecule undergoes covalent and enzymatic modification following translation. Post translational modification takes place in the endoplasmic reticulum and Golgi apparatus. Proteins that are produced using the codons of mRNA molecules undergo post translational modification to form a mature protein product.
Figure 02: Post Translational Modification
Post translational modifications are very important mechanisms in cellular signalling. This mechanism is particularly obvious when prohormones are converted to hormones in the body. Post translational modifications can occur on the amino acid side chains or the C or N terminals of the protein molecule. Furthermore, some examples of post translational modifications include phosphorylation (addition of phosphate group), lipidation (addition of lipid molecule, carbonylation (addition of carbon monoxide), SUMOylation (the covalent linkage to the SUMO protein), acylation (addition of acyl group), and alkylation (addition of alkyl group).
What are the Similarities Between Post Transcriptional and Post Translational Modification?
- Post transcriptional and post translational modifications are two different types of modifications that occur in protein biosynthesis.
- These modifications are extremely important for making fully functional protein molecules in the body.
- Both mechanisms mainly occur in the eukaryotes.
- Deregulation of both mechanisms leads to diseases in eukaryotes.
What is the Difference Between Post Transcriptional and Post Translational Modification?
Post transcriptional modification occurs after the transcription step of the protein synthesis, while post translational modification occurs after the translation step of the protein synthesis. Thus, this is the key difference between post transcriptional and post translational modification. Furthermore, post transcriptional modification is done to the precursor mRNA molecule, while post translational is done to the immature protein.
The below infographic presents the differences between post transcriptional and post translational modification in tabular form for side-by-side comparison.
Summary – Post Transcriptional vs Post Translational Modification
Post transcriptional and post translational modifications are two different types of modifications that occur during protein biosynthesis. They are extremely important for the survival of eukaryotes. Post transcriptional modification occurs after the transcription step of the protein synthesis, while post translational modification occurs after the translation step of the protein synthesis. So, this is the key difference between post transcriptional and post translational modification.
Reference:
1. “Overview of Post-Translational Modification.” Thermo Fisher Scientific – US.
2. “Post-Transcriptional Modifications (RNA Processing): Concise Medical Knowledge.” Lecturio, 5 Sept. 2022.
Image Courtesy:
1. “Post-transcriptional modification of pre-mRNA” By Kep17 – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Post-translational modification by cleavage” By Kep17 – Own work (CC BY-SA 4.0) via Commons Wikimedia