Steps of Transcription - Online Tutor, Practice Problems & Exam Prep

Transcription involves three key steps: initiation, elongation, and termination. During initiation, RNA polymerase binds to the promoter region of DNA, with eukaryotes requiring transcription factors for this process. In elongation, RNA polymerase synthesizes RNA by pairing free RNA nucleotides with the DNA template, moving in the 5' to 3' direction. Termination occurs when RNA polymerase reaches a terminator sequence, releasing the RNA molecule. In eukaryotes, this RNA is a premature form (pre-mRNA) that undergoes further processing before translation, unlike in prokaryotes where the RNA is ready for translation immediately.

1) Initiation of Transcription

In this video, we're going to begin our lesson on the steps of transcription. And so the process of transcription actually consists of 3 steps. The very first step is going to be initiation of transcription. The second step is going to be elongation of transcription, and the third and final step is going to be the termination of transcription. And so moving forward, we're going to talk about each of these three steps of transcription in their own separate video starting with initiation.

And so the initiation of transcription, initiation is referring to the beginning of transcription, and this involves the RNA polymerase binding to the promoter region on the DNA and separating the 2 strands of DNA. And so when those two strands of DNA are separated, that is going to allow the second step of transcription to begin. Now it turns out that transcription in eukaryotes and prokaryotes is a little bit different. And in prokaryotes, the RNA polymerase, which is the main enzyme involved in transcription, is going to bind to the promoter region on its own. However, in eukaryotes, transcription factor proteins are required for the RNA polymerase to bind to the promoter, and we'll be able to see that down below in our image.

Now, again, the unwinding of the DNA by the RNA polymerase is going to expose the DNA template strand, which the RNA polymerase can use the DNA template strand as a guide to build the RNA. And so if we take a look at our image, what you'll notice is on the left hand side, we're showing you initiation of transcription in prokaryotes, and on the right hand side, we're showing you initiation of transcription in eukaryotes. And so in the initiation, we know that the RNA polymerase is going to bind to the promoter and separate the 2 strands of DNA. And so here in our image, the pink circle is representing the RNA polymerase, and the RNA polymerase is going to bind specifically to the promoter region on the DNA. And so that's what you can see here.

The RNA polymerase binds specifically to this promoter region on the gene. And so, it will then unwind the DNA, separating the two strands, exposing the template strand of the DNA. You can also see downstream over here, you can see the terminator, which is going to be involved in the final process of transcription. Now over here on the right hand side, you'll see the same process, initiation of transcription, but in eukaryotes. And, really, the main difference that we're focusing on here is that in order for the RNA polymerase to bind to the promoter region in eukaryotes, these other proteins that are, we're representing as these yellow shapes here, are required, and those are the transcription factor proteins.

And so in eukaryotes, RNA polymerase requires transcription factor proteins, to bind to the promoter, and that will allow for the RNA polymerase to bind. And so in the eukaryotes here and in the background, you can see that the transcription factors are bound, and that helps recruit the RNA polymerase so that the RNA polymerase can also bind to the promoter. And then, again, transcription initiation is going to allow for the second step of transcription to begin, which is elongation. And so we'll talk more about elongation, the second step of transcription, in our next video. So I'll see you all there.

1) Elongation of Transcription

In this video, we're going to talk about the second step of transcription, which is the elongation of transcription. And so elongation is really just a word that means to elongate or make something longer. And the something that's being made longer is the RNA itself. And so elongation is the process where the RNA polymerase enzyme is building or synthesizing or elongating an RNA molecule. And so it does this by base pairing free RNA nucleotides that are floating around in the cell with the DNA template.

And so by the end of the process, the RNA molecule that's being built is going to be carrying the message that's encoded by the DNA. Now the RNA polymerase enzyme, which is, again, the primary enzyme involved in transcription, is going to continue to move across the gene, unwinding the DNA as it moves and building the RNA as it moves in the 5 prime to 3 prime direction of the RNA. And so if we take a look at our image down below at the elongation of transcription, you can see that the RNA polymerase enzyme, this big pink circle, is now bound to the promoter region on the DNA, and, the RNA polymerase has unwound the DNA. So you can see that the DNA on the inside is unwound, and it's beginning to elongate or build that RNA molecule by pairing free RNA nucleotides, these little guys here that are floating in the cell, each of these little squares represents free RNA nucleotides, and the RNA polymerase incorporates them into this growing RNA strand, by pairing these RNA nucleotides with the DNA template strand. And so this RNA polymerase is transcribing in this direction towards the right, so it will continue to transcribe the coding sequence.

And so, this is representing the process of elongation. And, of course, during elongation, the mRNA, the molecule, RNA molecule is growing. It is elongating. And it's elongating from its 5 prime end to its own 3 prime end. And the RNA polymerase will continue to elongate in this direction, continue to transcribe the gene until it reaches this terminator sequence that you see on the end here.

And we'll talk more about this termination process in our next video. Now one thing that's important to note here is that in eukaryotic organisms, the RNA that is first transcribed is not the final RNA. Instead, it's a premature RNA or just a pre-mRNA. And so we'll get to talk more about the pre-mRNA later in our course. Now it's also interesting to note that a single gene can actually be transcribed simultaneously by several RNA polymerases to make more RNA if it's needed.

And so while this mRNA here is being built by this RNA polymerase, it is possible for a second RNA polymerase to come and bind to the promoter and to transcribe this gene simultaneously where there's multiple RNA molecules being built simultaneously from the same gene. And so, that is just simultaneously from the same gene. And so, that is just something to keep in mind. And so this here concludes our brief introduction to the elongation of transcription. And so in our next video, we'll get to talk about the 3rd and final step of transcription, which is the termination of transcription.

So I'll see you all there.

3) Termination of Transcription

In this video, we're going to talk about the third and final step of transcription, which is the termination of transcription. Termination refers to putting something to an end. The termination of transcription is the process that results in the end of transcription to produce an RNA molecule. It turns out that prokaryotes and eukaryotes differ in the way that they terminate transcription. Specifically, in eukaryotes, eukaryotic termination forms a premature RNA molecule.

This premature RNA molecule is not the final molecule in eukaryotic organisms. The premature RNA molecule in eukaryotic organisms requires further modification through RNA processing, which we'll get to talk more about as we move forward in our course. However, in prokaryotes, the RNA molecule formed is not premature and does not require RNA processing. The premature RNA is only found in eukaryotic organisms. When looking at our image below, at the termination of transcription, what you'll notice is that the RNA polymerase is reaching this terminator sequence here, and the terminator sequence on the DNA initiates the process of termination.

Ultimately, termination results in the RNA polymerase being released and the RNA molecule being released. In prokaryotic organisms, the RNA molecule is ready for translation immediately. However, in eukaryotic organisms, the RNA is a premature RNA, a pre-mRNA. This is not going to be the final version of the RNA in eukaryotic organisms. This RNA would have to undergo RNA processing in eukaryotic organisms before translation can take place.

Again, this is only applicable for eukaryotes, not for prokaryotes. This concludes our brief introduction to the termination of transcription, and we'll be able to get some practice applying these concepts as we move forward in our course. I'll see you all in our next video.

During which stage of transcription do the following processes take place?

1. RNA polymerase binds to the promoter.

2. The RNA transcript is released.

3. The RNA transcript extended.

• A. 1-termination; 2-initiation; 3-elongation.
• B. 1-initiation; 2-elongation; 3-termination.
• C. 1-elongation; 2-termination; 3- initiation.
• D. 1-initiation; 2-termination; 3-elongation.
• E. 1-termination; 2-elongation; 3-initiation.

Transcription in eukaryotes requires which of the following molecules in addition to RNA polymerase?

• A. Anticodons.
• B. Ribosomes and tRNA.
• C. Transcription factors.
• D. Aminoacyl-tRNA synthetase.

Which of the following is the correct transcript of mRNA for the following DNA template?

DNA Template: 3'-ATGAAGCCGAGTCAT-5'.

• A. 3'-TACTTCGGCTCAGTA-5'.
• B. 3'-AUGACUCGGCUUCAU-5'.
• C. 3'-UACUUCGGCUCAGUA-5'.
• D. 3'-ATGACTCGGCTTCAT-5'.

During transcription of DNA to RNA:

• A. The RNA polymerase moves along the DNA in the 5' to the 3' direction.
• B. The 3' end of the RNA molecule is produced first.
• C. The RNA polymerase must first bind to a promoter sequence.
• D. Transcription is always initiated at a "start codon".

What happens during the initiation step of DNA transcription?

• A. The mRNA detaches from the RNA polymerase as the RNA polymerase leaves the DNA strand.
• B. RNA polymerase attaches to the DNA at the promoter sequence of the gene.
• C. A ribosome attaches to the initiation codon of a completed mRNA strand.
• D. RNA polymerase moves along the template strand of the DNA creating an mRNA strand.

Which of the following properties is NOT shared by RNA polymerase and DNA polymerase?

• A. Can initiate strand synthesis.
• B. Dependent on a DNA sequence template.
• C. Catalyzes phosphodiester bond formation.
• D. Cannot proofread using a 3'-to-5' exonuclease activity.
• E. Polymerizes nucleotides in a 5'-to-3' direction.

Here’s what students ask on this topic:

What are the three main steps of transcription?

The three main steps of transcription are initiation, elongation, and termination. During initiation, RNA polymerase binds to the promoter region of the DNA, with transcription factors required in eukaryotes. In elongation, RNA polymerase synthesizes the RNA strand by pairing free RNA nucleotides with the DNA template, moving in the 5' to 3' direction. Termination occurs when RNA polymerase reaches a terminator sequence, releasing the newly formed RNA molecule. In eukaryotes, this RNA is a premature form (pre-mRNA) that undergoes further processing before translation, unlike in prokaryotes where the RNA is ready for translation immediately.

How does transcription initiation differ between prokaryotes and eukaryotes?

In prokaryotes, RNA polymerase binds directly to the promoter region of the DNA to initiate transcription. In contrast, eukaryotes require additional proteins called transcription factors to help RNA polymerase bind to the promoter. These transcription factors assemble at the promoter region, facilitating the binding of RNA polymerase and the subsequent unwinding of the DNA strands to expose the template strand for RNA synthesis.

What happens during the elongation step of transcription?

During elongation, RNA polymerase synthesizes the RNA strand by adding RNA nucleotides that are complementary to the DNA template strand. The enzyme moves along the DNA in the 5' to 3' direction, unwinding the DNA as it goes and elongating the RNA molecule. This process continues until RNA polymerase reaches a terminator sequence, signaling the end of transcription.

What is the role of the terminator sequence in transcription?

The terminator sequence in transcription signals the end of the RNA synthesis process. When RNA polymerase reaches this sequence, it triggers the release of both the RNA polymerase enzyme and the newly synthesized RNA molecule. In prokaryotes, the RNA is immediately ready for translation. In eukaryotes, the RNA is a premature form (pre-mRNA) that requires further processing before it can be translated into a protein.

Why is RNA processing necessary in eukaryotes but not in prokaryotes?

RNA processing is necessary in eukaryotes because the initial RNA transcript, known as pre-mRNA, contains non-coding regions (introns) that need to be removed. Additionally, a 5' cap and a poly-A tail are added to the pre-mRNA to protect it from degradation and assist in its export from the nucleus. In prokaryotes, the RNA transcript is immediately functional and ready for translation, as it does not contain introns and does not require these modifications.