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

Transcription is the process where DNA serves as a template to synthesize RNA, primarily facilitated by the enzyme RNA polymerase. This process occurs in three stages: initiation, elongation, and termination, with RNA synthesized in the 5' to 3' direction. Only one DNA strand, the template strand, is used for transcription, while the coding strand has the same sequence as the RNA, except for uracil replacing thymine. Understanding the concepts of upstream and downstream is crucial, as they refer to regions before and after the gene start site, respectively.

Overview of Transcription

Hi. In this video, we're going to be doing an overview of transcription. Transcription is the process of using DNA as a template, and that template DNA is used to synthesize RNA. DNA is the template, RNA is what is created. Now, RNA polymerase is the enzyme that is responsible for transcribing the DNA and turning it into an RNA copy. There are many different types of RNA polymerases, and we'll talk about those in a different video, but each RNA polymerase makes a different type of RNA. There's ribosomal RNA, transfer RNA, messenger RNA, noncoding RNAs, and there are different RNA polymerases for each one of those RNAs. It's always important in biology to understand the direction that things are happening in, so RNA transcripts are synthesized in the 5 prime to 3 prime direction. This means that the new strand is produced 5 prime to 3 prime. How this happens is new RNTPs or new RNA nucleotides are added onto the 3 prime end. There's a hydroxyl group there, and that hydroxyl group is important for adding new nucleotides in, and that hydroxyl group is on the 3 prime end.

DNA is double-stranded, and that means that the information for the genes is actually found on both strands. They're complementary, but all that information is the same. However, each gene is only transcribed using one strand. So even though it's a double helix, even though there are two strands, only one of those strands correctly transcribes or is used to transcribe the RNA that will go on to create that protein. This is important. Oftentimes, when we talk about transcription, we use two terms: upstream and downstream. Upstream means that it starts before the gene start site. It's a sequence of DNA that's before where the gene starts, and downstream means there's an area of DNA that is after the gene start site. Upstream comes before the gene starts and downstream comes after the gene starts. This is because an overview transcription occurs in 3 stages: initiation, elongation, and termination, and these stages are slightly different between prokaryotes and eukaryotes, and we'll talk about those differences in other videos.

But here we have an example, so here's the RNA polymerase, RNA P, that's what that stands for. And you can see there are 2 strands of DNA, going 5 prime to 3 prime and 3 prime to 5 prime. Now the template strand, so this is the strand that's being used by the polymerase, see it's attached onto the template strand, is being used by the RNA polymerase to make RNA, and it synthesizes it 5 prime to 3 prime. So you can see that the blue strand here is 5 prime and the black strand, which is the template strand, is 3 prime here to 5 prime here. Understanding this orientation is important, and that means the template strand is what's used to create, and this is going to be complementary, right? These are pairing here. So the template strand will be complementary and the coding strand will be the exact copy.

What I mean is that if you start out with DNA and you have bases on each side, they are complementary, meaning that if you have A here, you're going to have T here, and if you have C here, you're going to have G here. Now when the RNA polymerase comes in, it binds here, say RNA P. That means that when it's synthesizing RNA, what it's doing is it's putting U here, G here, and so this sequence isn't the exact same as the template strand, but it is the exact same as the coding strand with the exception of, RNA has uracil instead of thymine.

So if I were to give a sequence, and I were to say here's the template strand and here's the coding strand, and I were to ask what is the RNA sequence? If the template strand is ATCGATCG, that would mean the coding strand is TAGCTAGC. So what is the RNA sequence? Can you guess? It is the template strand that RNA polymerase binds to, which means that the RNA that's read is UAGCUAGC. Notice here that the template strand and the RNA are complementary, but the coding strand and the RNA are the same sequence with the exception of uracil and thymine. So oftentimes, you'll be given a question that asks, here is the coding strand, what is the sequence of the RNA? If you're given the coding strand, know that it is the exact same sequence except that uracil is exchanged for thymine. But if you're given the template strand, that's the complementary. That's the difference between the two. So, that's the overview of transcription, so with that, let's now move on.

Transcription is the process of which of the following?

• A. DNA → Protein
• B. DNA → RNA
• C. DNA → DNA
• D. RNA → DNA

Only one strand of DNA is used during transcription of a gene.

• A. True
• B. False

If a DNA sequence is upstream of where the gene is, where is these sequence?

• A. Before the gene
• B. After the gene
• C. In the middle of an intron
• D. At the start of the first exon

Here’s what students ask on this topic:

What is the role of RNA polymerase in transcription?

RNA polymerase is the enzyme responsible for synthesizing RNA from a DNA template during transcription. It binds to the DNA at the promoter region and unwinds the DNA strands. Using one of the DNA strands as a template, RNA polymerase adds RNA nucleotides in the 5' to 3' direction, creating a complementary RNA strand. Different types of RNA polymerases exist, each synthesizing different types of RNA, such as messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). The enzyme plays a crucial role in the initiation, elongation, and termination stages of transcription.

What are the three stages of transcription?

Transcription occurs in three stages: initiation, elongation, and termination. During initiation, RNA polymerase binds to the promoter region of the DNA, causing the DNA strands to unwind. In the elongation stage, RNA polymerase moves along the template strand, adding RNA nucleotides in the 5' to 3' direction to synthesize the RNA strand. Finally, in the termination stage, RNA polymerase reaches a terminator sequence, causing the newly synthesized RNA to be released and the RNA polymerase to detach from the DNA. These stages ensure the accurate synthesis of RNA from the DNA template.

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

In transcription, the template strand is the DNA strand used by RNA polymerase to synthesize RNA. It is complementary to the RNA sequence being produced. The coding strand, on the other hand, has the same sequence as the RNA (except that thymine (T) in DNA is replaced by uracil (U) in RNA). While the template strand is directly involved in the synthesis process, the coding strand serves as a reference for the RNA sequence. Understanding the roles of these strands is crucial for interpreting genetic information.

What do the terms 'upstream' and 'downstream' mean in the context of transcription?

In the context of transcription, 'upstream' and 'downstream' refer to the relative positions on the DNA strand. 'Upstream' denotes the region of DNA that is before the gene start site, while 'downstream' refers to the region after the gene start site. These terms help in identifying the locations of various regulatory elements and sequences that influence the transcription process. For example, promoters are typically found upstream of the gene, while terminator sequences are located downstream.

In which direction is RNA synthesized during transcription?

During transcription, RNA is synthesized in the 5' to 3' direction. This means that new RNA nucleotides are added to the 3' end of the growing RNA strand. The RNA polymerase reads the DNA template strand in the 3' to 5' direction, ensuring that the RNA strand is complementary to the template strand. This directionality is crucial for the accurate synthesis of RNA and the proper functioning of the genetic code.