Introduction to Transcription - Online Tutor, Practice Problems & Exam Prep

Transcription is the process where DNA is converted into RNA, beginning at the promoter and ending at the terminator. RNA polymerase, the key enzyme, binds to the promoter and synthesizes RNA from the template strand, creating a sequence that mirrors the coding strand, with uracil replacing thymine. This process occurs in the 5' to 3' direction, utilizing base pairing rules. Understanding transcription is crucial for grasping how genes encode proteins, as it lays the foundation for subsequent translation into functional products.

Introduction to Transcription

In this video, we're going to begin our introduction to transcription. Recall from our previous lesson video that transcription is the process that builds RNA by using the DNA within a gene as the coding template, and so this is the process of building RNA. Also recall from our previous lesson videos that genes are really referring to small units of DNA that encode a product, for example, a protein. Genes, in order to create a protein, will need to be both transcribed and translated. Here we're talking about the first step of the process which is transcription, being transcribed.

Now, in order to better understand transcription, it's helpful to describe some specific sequences of DNA that mark where the transcription of a gene begins and ends. The first sequence of DNA that you should note is called the promoter. The promoter is a small stretch of DNA sequences where transcription begins. The promoter is just the site where the RNA polymerase is going to attach, and the RNA polymerase is the primary enzyme involved in transcription. As we mention below, the RNA polymerase is an enzyme, the primary enzyme, that is going to polymerize or build RNA from scratch.

It turns out that RNA polymerases do not need a primer like DNA polymerases do. RNA polymerase does not require a primer. We're going to talk a lot more about RNA polymerase and transcription as we move forward in our course here. It's important to note that the promoter is the sequence where transcription begins because this is the site where the RNA polymerase first attaches. The terminator, on the other hand, is also a stretch of DNA sequences, but this is where transcription is going to end.

If we take a look at our image below, what you'll notice is on the far left, we have a chromosome, a replicated chromosome, which consists of DNA and protein. If you unravel this chromosome, you'll find that there is DNA in here, and some of this DNA are genes. They encode a product like a protein. If we take a look at a typical gene, and zoom into it, what you'll find is that it's going to have a green region here that we're referring to as the promoter.

The promoter is, again, the small stretch of DNA sequences that allow for the RNA polymerase to bind. This pink structure that you see here is the RNA polymerase, the primary enzyme involved with transcription. The RNA polymerase will bind to the gene specifically at this promoter region, and then the RNA polymerase will transcribe the coding sequence of this gene. The terminator over here at the end is, of course, where transcription is going to end.

Collectively, the promoter, the coding sequence, and the terminator, this entire region right here, is referred to as the gene. Sometimes there are other important sequences that surround a gene, and so it's important to be able to refer to the directionality of those sequences that might be outside of the gene. They use the terms upstream of the gene and downstream of the gene. It turns out that downstream of the gene is referring to DNA sequences in the same direction as transcription. You can think of little fish downstream, and the downstream is going to represent DNA sequences outside of the gene that are in the same direction of transcription. The opposite direction is going to be referred to as upstream. Upstream refers to DNA sequences in the opposite direction of transcription. Again, the RNA polymerase binds at the promoter and transcribes in this direction, but upstream of the gene is in the opposite direction of the transcription direction.

This here concludes our brief introduction to transcription. As we move forward in our course, we're going to continue to learn more and more about transcription. I'll see you all in our next video.

Which of the following is the best definition of a gene?

• A. An RNA molecule transcribed from a sequence of DNA.
• B. A stretch of DNA that can be transcribed.
• C. A sequence of DNA where the process of transcription ends.
• D. A sequence of DNA that encodes a product like an RNA or a protein.
• E. A sequence of DNA where the process of transcription begins.

Which of the following statements is false?

• A. Transcription is the process that creates an RNA product from a sequence of DNA.
• B. RNA polymerase builds RNA molecules from a DNA template.
• C. A promoter is a sequence of DNA within a gene where RNA polymerase can begin transcription.
• D. RNA polymerase, like DNA polymerase, requires a primer to begin RNA synthesis.

Overview of Transcription

In this video, we're going to do an overview of the entire process of transcription. However, it's important to keep in mind that as we continue to move forward in our course, we're going to continue to break down transcription in more detail. And later in our course, in a separate video, we'll talk about the individual steps of transcription in more detail. And here in this video, we're just doing an overview of the entire process. And so it's important to note that the two strands of DNA in a gene are referred to as either the coding strand or the template strand.

Now, it turns out that during transcription, the RNA molecules that are being built are going to have the same exact sequence as the coding DNA strand, and the template DNA strand is just going to serve as a template for building the RNA. But ultimately, the RNA molecule is going to be carrying the message that's in the coding DNA strand. And so the only difference between the RNA sequence and the coding DNA sequence is going to be the fact that it's going to be replacing all of the T's or thymines with U's or uracils. And recall that this is because RNA has uracils, whereas DNA is going to have thymines. And we'll be able to see an example and application of this down below in our example.

Now, it's also important to note that during transcription, the RNA molecule itself is going to be built from its 5' end to its 3' end, and it's going to be built by pairing free RNA nucleotides that are floating around in the cell on a DNA template. And so we'll be able to see that down below in our image over here on this side. Now, this nucleotide pairing is going to occur via Watson and Crick base pairing, which, recall, we already covered in our previous lesson videos, which basically says that A's or adenines will pair with T's or thymines. Or in the case of DNA base pairing with RNA, A's are going to be base pairing with U's, because remember that in RNA, U's are going to replace the T's. And then, of course, we know that G's are going to base pair with C's.

And so, if we take a look at our image down below, we can better understand the overall overview of transcription. And so this example here wants us to determine the sequence for the template DNA strand and for the mRNA transcript given the following coding strand. And so, when we take a look at this side of the image over here, what you'll notice is we have a DNA molecule. And recall that DNA has 2 strands, and each of these two strands, one of them is going to be the coding strand and the other one's going to be the template strand. In this case, the coding strand is at the top here and the template strand is the one on the bottom.

And so it wants us to determine the template DNA strand sequence along with the mRNA transcript sequence that's down below. And so, what's important to note here is that when we look at the coding sequence, coding strand sequence, it is GGA T C. And we know that through Watson and Crick base pairing that the G's are going to base pair with C's, and so these G's here will base pair with C's on the DNA. So we know that C's are going to go in these positions and that A's are going to base pair with T's in the DNA, and so, we will put T's here, and T's will base pair with A's, and, of course, C's base pair with G's. And so this sequence here is the sequence of the template strand.

Now, of course, the process of transcription represented by this arrow is going to use the DNA to build RNA. And the RNA, as we mentioned up above, is going to have the same sequence as the coding DNA strand with this exception right here, replacing the T's with U's. And so what we can see here is that the coding sequence strand is right here at the top, and RNA is going to have the same sequence as the coding strand. So it is going to be GGA, and then, of course, replacing the T's with U's, as we mentioned here, replacing the T's with U's. And so here, instead of having a T at this position, we're going to have a U.

And then, of course, the C here is going to go right here. And so this will be the sequence of the RNA. Now it turns out that in eukaryotic cells, the RNA that is first made is called a pre-mRNA transcript because it's not fully mature, but we're going to talk more details about that later in our course. Now over here on the right, we're kind of showing you more of a zoom out of the overall process of transcription. And recall that the RNA polymerase enzyme, which is this big pink circle in the background, is the primary enzyme involved with transcription.

And so it will bind to the promoter region on a gene and start to transcribe the gene. And so when it transcribes a gene, it's going to be building the RNA, and the RNA is going to be built from its 5' end to its 3' end, again, by pairing free RNA nucleotides that are floating around in the cell on a DNA template. And so you can see that this RNA is being built from its 5' end over here towards its 3' end over here. And the direction of the RNA polymerase is to the right, so transcription is proceeding to the right. And so what you'll notice is that the DNA is going to unwind, and you can see that there's a coding strand and, again, a template strand.

And the RNA, of course, is going to end up taking the same exact sequence as the coding strand. And again, this bottom one that's down here is going to be the template strand of DNA. Now you'll notice that there is going to be a region here highlighted by this box, which is representing an RNA DNA hybrid region. And so, you can see that these free RNA nucleotides that are floating around in the cell are going to be incorporated into this RNA molecule by the RNA polymerase enzyme. And so this here is representing the overall overview of transcription.

And again, as we move forward in our course, we're going to break down this process of transcription in more detail, looking at it step by step. But for now, this here concludes our overview of transcription, and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.

The strand of DNA that has the same sequence as the RNA molecule being created during transcription is the:

• A. Lagging strand.
• B. Leading strand.
• C. Coding strand.
• D. Template strand.
• E. Parent strand.

Transcription is sometimes described as a process in which RNA is "copied" from the template strand of DNA. This statement is potentially misleading since _____.

• A. The nucleotides in RNA contain ribose and cannot be an exact copy of DNA.
• B. RNA molecules contain uracil instead of thymine and cannot be an exact copy of DNA.
• C. The RNA transcript has a sequence complementary to the template.
• D. The RNA transcript and the DNA template strand are antiparallel.
• E. All of the above.

Here’s what students ask on this topic:

What is the role of RNA polymerase in transcription?

RNA polymerase is the primary enzyme involved in transcription. It binds to the promoter region of a gene and synthesizes RNA by using the DNA template strand. Unlike DNA polymerase, RNA polymerase does not require a primer to start synthesis. It builds the RNA molecule in the 5' to 3' direction by pairing free RNA nucleotides with the complementary bases on the DNA template strand. The resulting RNA sequence mirrors the coding DNA strand, with uracil (U) replacing thymine (T). This enzyme is crucial for converting genetic information from DNA into RNA, which can then be translated into proteins.

What are the promoter and terminator regions in transcription?

The promoter and terminator regions are specific DNA sequences that mark the beginning and end of transcription, respectively. The promoter is a small stretch of DNA where RNA polymerase binds to initiate transcription. It is located upstream of the gene's coding sequence. The terminator, on the other hand, is a sequence that signals the end of transcription. When RNA polymerase reaches the terminator, it releases the newly synthesized RNA molecule and detaches from the DNA. These regions ensure that transcription occurs at the correct location and produces the correct RNA transcript.

What is the difference between the coding strand and the template strand in transcription?

In transcription, the DNA of a gene consists of two strands: the coding strand and the template strand. The coding strand has the same sequence as the RNA transcript, except that thymine (T) is replaced by uracil (U) in RNA. The template strand, on the other hand, serves as the actual template for RNA synthesis. RNA polymerase reads the template strand and synthesizes a complementary RNA molecule. Therefore, the RNA sequence is complementary to the template strand but identical to the coding strand, with the substitution of U for T.

How does base pairing work during transcription?

During transcription, base pairing follows specific rules to ensure accurate RNA synthesis. Adenine (A) in the DNA template strand pairs with uracil (U) in RNA, while cytosine (C) pairs with guanine (G). Guanine (G) pairs with cytosine (C), and thymine (T) in the DNA pairs with adenine (A) in RNA. This base pairing occurs via Watson and Crick base pairing rules. The RNA polymerase enzyme facilitates this process by adding the correct RNA nucleotides to the growing RNA strand, ensuring that the RNA sequence is complementary to the DNA template strand.

What is the significance of the 5' to 3' direction in RNA synthesis?

RNA synthesis occurs in the 5' to 3' direction, meaning that RNA polymerase adds nucleotides to the 3' end of the growing RNA molecule. This directionality is crucial for the proper synthesis and function of RNA. The 5' to 3' direction ensures that the RNA molecule is synthesized in a manner that allows for proper base pairing with the DNA template strand. Additionally, this directionality is important for subsequent processes, such as RNA processing and translation, where the 5' and 3' ends of the RNA molecule play specific roles in stability, localization, and protein synthesis.