Processing of pre-mRNA: Study with Video Lessons, Practice Problems & Examples

In eukaryotic cells, DNA contains exons, which code for proteins, and introns, which do not. During transcription, both are copied into pre-mRNA (hnRNA). The processing phase involves spliceosomes that remove introns and splice exons together, resulting in mature mRNA. This mature mRNA exits the nucleus to the ribosomes for protein synthesis. Understanding this process is crucial for grasping how genetic information is expressed and utilized in cellular functions.

Processing of Pre-mRNA Concept 1

Hey everyone. So, in this video, we're going to take a look at the processing of pre-mRNA. Now, with Eukaryotic species, mainly animals and plants, we're going to say DNA contains segments called Exons and Introns. Exons are the portions that code for proteins, while Introns are the portions that do not. Now, with transcription, we're going to say it copies both exons and introns to pre-mRNA, also called hnRNA. You might hear these two terms being used interchangeably. They're the same thing. Now, here, we have a process called processing where spliceosomes are going to process our pre-mRNA to produce mature mRNA for protein synthesis. Now, it cuts the introns out, and it's going to splice the exons together. Our memory tool here is that exons are expressed. If we take a look here at this image, we have our gene, our informational strand. It has exons and introns involved. Through transcription, we still have our exons and introns involved because we're just copying it. This is what we call our pre-mRNA or our hnRNA. Now, this starts to undergo processing. And through processing with our spliceosome, we're cutting the connections between our exons and our introns. And we're going to remove the introns, keeping the exons around. We're going to splice them together. Now we have only exons remaining at the end, and this represents our mature mRNA. Now, recall that when we talk about mRNA, it's going to then move out of the nucleus to the Ribosomes in the Cytoplasm for Protein Synthesis. So, just remember, we're copying a segment of our DNA to make this initial pre-mRNA. It still needs to be processed where we get rid of the introns so that the exons can be expressed later on. This is important so that we are left with what's necessary for proper protein synthesis.

Processing of Pre-mRNA Example 1

Here it says, which of the following statements is incorrect about hRNA, hnRNA processing? Remember, hnRNA is the same thing as pre mRNA. It's the non processed version of mature mRNA. Now, here, hnRNA is processed inside the nucleus in structures called spliceosomes. That's true. Introns that do not code for proteins are removed from hnRNA during processing. That is also true. Spliceosomes join the exons together after introns are removed. Yes, that's correct. Remember, the memory tool: exons are expressed. They're left behind and then spliced together so that they eventually leave the nucleus to go towards the ribosomes, which are in the cytosol for protein synthesis. hnRNA is processed to reduce its size so that it can fit inside ribosomes. Nor did we talk about having to cut out the introns because of spatial issues. It's not about size involved. We're just getting rid of the portions that do not code for proteins. Remember, the whole point of making mRNA is that we can eventually make the necessary proteins from it. So we just gotta get rid of the portions that don't help us code for protein. So here, the answer here would be option d.

The underlined sections of the pre-mRNA below are introns. Write the sequence for mature mRNA.

5’ GCC CGA UUU AUC AGG GAC CCA 3’

• A. 5’ GCC UUU AUC AGG 3’
• B. 5’ GCC UUU GAC CCA 3’
• C. 5’ GCC CGA AUC AGG 3’
• D. 5’ GCC CGA UUU CCA 3’

Here’s what students ask on this topic:

What is the role of spliceosomes in the processing of pre-mRNA?

Spliceosomes are essential molecular complexes in the processing of pre-mRNA. They are responsible for removing introns, which are non-coding regions, from the pre-mRNA. The spliceosome cuts the connections between exons and introns, excising the introns and splicing the exons together. This process results in the formation of mature mRNA, which contains only the coding sequences necessary for protein synthesis. The mature mRNA then exits the nucleus and travels to the ribosomes in the cytoplasm, where it directs the synthesis of proteins. Understanding the role of spliceosomes is crucial for grasping how genetic information is accurately expressed in eukaryotic cells.

What are exons and introns in the context of pre-mRNA processing?

Exons and introns are segments of DNA that are transcribed into pre-mRNA. Exons are the coding regions that contain the information necessary to produce proteins. In contrast, introns are non-coding regions that do not contribute to protein synthesis. During the processing of pre-mRNA, spliceosomes remove the introns and splice the exons together to form mature mRNA. This mature mRNA, which consists only of exons, is then used in the cytoplasm for protein synthesis. The distinction between exons and introns is fundamental to understanding how genetic information is edited and utilized in eukaryotic cells.

How does pre-mRNA differ from mature mRNA?

Pre-mRNA, also known as hnRNA, is the initial transcript that is produced during transcription. It contains both exons (coding regions) and introns (non-coding regions). In contrast, mature mRNA is the result of the processing of pre-mRNA, where introns are removed, and exons are spliced together by spliceosomes. Mature mRNA contains only the coding sequences necessary for protein synthesis. This mature mRNA exits the nucleus and travels to the ribosomes in the cytoplasm, where it directs the synthesis of proteins. The key difference lies in the presence of introns in pre-mRNA and their absence in mature mRNA.

Why is the removal of introns important in mRNA processing?

The removal of introns is crucial in mRNA processing because introns are non-coding regions that do not contribute to protein synthesis. If introns were not removed, the resulting mRNA would contain sequences that could disrupt the translation process, leading to the production of non-functional or harmful proteins. By removing introns and splicing exons together, the cell ensures that the mature mRNA contains only the necessary coding sequences for accurate protein synthesis. This precise editing process is essential for the proper expression and function of genetic information in eukaryotic cells.

What happens to mature mRNA after it is processed?

After mature mRNA is processed, it exits the nucleus and travels to the ribosomes in the cytoplasm. Ribosomes are the cellular machinery responsible for translating the mRNA sequence into a specific protein. The mature mRNA serves as a template, guiding the ribosomes in assembling amino acids in the correct order to form a functional protein. This process, known as translation, is the final step in the expression of genetic information, allowing the cell to produce the proteins necessary for its various functions and activities.