Eukaryotic Transcriptional Control - Online Tutor, Practice Problems & Exam Prep

Eukaryotic transcription control involves transcription factors that bind to regulatory DNA regions, influencing gene expression. General transcription factors are essential for all genes, recruiting RNA polymerase to the promoter, particularly the TATA box. Specific transcription factors, however, enhance transcription for particular genes by binding to control elements, which can be distal (enhancers) or proximal to the promoter. Understanding these mechanisms is crucial for grasping gene regulation and expression in eukaryotic cells.

Introduction to Transcription Factors

In this video, we're going to begin our lesson on eukaryotic transcription control. Eukaryotes can regulate their gene expression by utilizing DNA binding proteins, which bind to regulatory regions in a gene to help control transcription. These DNA binding proteins are actually called transcription factors. We are introducing transcription factors here. Recall from our previous lesson videos that transcription initiation in eukaryotes requires a complex of transcription factors bound to a promoter sequence. Transcription factors, as their name implies, are important for transcription, and more specifically, they are proteins that bind to specific DNA sequences and regulate transcription initiation and help promote transcription. There are two main types of transcription factors in eukaryotes: general transcription factors, and specific transcription factors.

In the image below, we provide brief information on general and specific transcription factors. As we move forward in our course, we will discuss more details about these. Notice in this image, we show a DNA molecule in the background, which has two strands, one that goes 5' to 3' from left to right, and the other strand goes 5' to 3' from right to left. The promoter region is highlighted in green, followed by the coding sequence of the gene. General transcription factors bind to the promoter region and are required for the transcription of all genes, which is why they are called general transcription factors. Specific transcription factors, on the other hand, do not necessarily bind directly to the promoter but can bind to other regulatory regions around a gene. These specific transcription factors are not required for all genes, but are required for the transcription of specific genes. Some genes require specific transcription factors, but all genes require general transcription factors.

As we move forward in our course, we will continue to discuss more details about general and specific transcription factors. But for now, this concludes our brief introduction to eukaryotic transcriptional control and transcription factors, and I'll see you all in our next video.

General Transcription Factors

In this video, we're going to talk more details about general transcription factors. Recall from our last lesson video that general transcription factors are called general transcription factors because they're required for the transcription of every gene in the genome of all genes. They're general because they are applied to all genes. General transcription factors are important for recruiting RNA polymerase to the promoter region of a gene. Of course, when RNA polymerase is recruited to the promoter region, then transcription can proceed.

What we haven't yet discussed is that the transcription initiation complex, which is commonly abbreviated as just TIC, is really just the entire complex of all general transcription factors and the RNA polymerase complex together. There is a specific sequence associated with eukaryotic organisms called the TATA box. The TATA box is literally just a sequence of adenines and thymines that repeat, and is located in the promoter that recruits the TIC, the transcription initiation complex. The TATA box is important for recruiting general transcription factors as well as the RNA polymerase.

If we take a look at our image down below, notice again we're showing you how general transcription factors will bind to the TATA box in the promoter and recruit RNA polymerase for transcription. Notice again, over here on the left-hand side, we're showing you this miniature map of our lesson, and we're focused on transcription here, transcriptional control, and part of that includes general transcription factors. Notice that within the promoter of the DNA, we have a specific region that has the TATA repeats, specifically the TATA box. The TATA box is important for recruiting general transcription factors.

These general transcription factors are represented as these little yellow structures that you see right here. The general transcription factors will bind to the TATA box within the promoter region. After the general transcription factors bind, they are important for recruiting RNA polymerase, allowing RNA polymerase to bind to the promoter region. Once the RNA polymerase is bound to the TATA box within the promoter region along with all of the general transcription factors, this is what we refer to as the transcription initiation complex or the TIC. At this point, transcription can proceed and start to transcribe the coding sequence.

This here concludes our brief introduction to general transcription factors. As we move forward, we'll compare this to specific transcription factors, which we'll talk about in our next video. So I'll see you all there.

Specific Transcription Factors

In this video, we're going to talk more about specific transcription factors. Recall from our previous lesson videos that specific transcription factors are only required for increasing the transcription of a specific gene. So, specific transcription factors are not required for all genes; they're only required for some specific genes. These specific transcription factors actually bind to regions of DNA called control elements. Control elements are really just regions of noncoding DNA where specific transcription factors will bind. There are two different types of control elements: distal control elements, which are distant from the promoter sequence, and proximal control elements, which are located close or in close proximity to the promoter sequence. A group of distal control elements is referred to as enhancers.

An enhancer is defined as a group of distal control elements where specific transcription factors will bind. Let's take a look at our image below to get a better understanding of these specific transcription factors. Specific transcription factors can bind either to distal or proximal control elements. On the left-hand side, we have our little miniature version of the map where you can see that transcription and transcriptional regulation occurs within the nucleus of eukaryotic cells.

Notice, number 1, what we're showing you are the distal control elements. A group of distal control elements is referred to as an enhancer. You can see three different regions here that are these distal control elements. Notice that they are some distance away from the promoter region of the gene. This little horizontal, 2 slash bar here just represents that it is a significant distance away from the promoter region. Then, number 2, what we have are the proximal control elements. These two yellow regions here are fairly close to the promoter region.

Notice that these specific transcription factors, symbolized here with pink shapes, can either bind to the distal or the proximal control elements, as you can see here, binding to the distal. Below, in our image here, specific transcription factors binding to the proximal control elements. However, the general transcription factors discussed in our previous lesson videos will bind specifically to the promoter region and are needed for all genes in general. The idea here is that specific transcription factors can either bind to proximal control elements or distal control elements. This concludes our brief lesson on specific transcription factors, 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.

Regulatory segments of DNA that function to increase transcription levels in eukaryotes are called:

• A. promoters.
• B. silencers.
• C. enhancers.
• D. transcriptional start sites.
• E. activators.

Which of the following statements correctly describes the primary difference between enhancers and proximal control elements?

• A. Enhancers are transcription factors; proximal control elements are DNA sequences.
• B. Enhancers increase transcription of specific genes; proximal control elements inhibit transcription of specific genes.
• C. Enhancers are located thousands of nucleotides away from the promoter; proximal control elements are close to the promoter.
• D. Enhancers are DNA sequences; proximal control elements are transcription factors.

Which of the following is NOT true regarding the differences of transcription in eukaryotes and prokaryotes?

• A. Eukaryotes use multiple transcription factors to help initiate transcription.
• B. Most eukaryotes have regulatory sites that are close to their promoters.
• C. Most prokaryotes transcribe multiple genes under the regulation of a single operon.
• D. Prokaryotic transcription factors usually interact directly with RNA polymerase while eukaryotic transcription factors do not.

Which of the following statements about transcription factors is incorrect:

• A. The transcription initiation complex is composed of RNA polymerase, general and specific transcription factors.
• B. General transcription factors help initiate transcription of all eukaryotic genes.
• C. Specific transcription factors do not bind the promoter of a gene, but to control elements associated with the gene.
• D. The transcription initiation complex associates with the TATA box of the promoter to begin transcription.

Here’s what students ask on this topic:

What are general transcription factors and their role in eukaryotic transcription?

General transcription factors are proteins essential for the transcription of all genes in eukaryotic cells. They bind to the promoter region of DNA, specifically to a sequence known as the TATA box. Their primary role is to recruit RNA polymerase to the promoter, forming the transcription initiation complex (TIC). This complex is crucial for the initiation of transcription, allowing RNA polymerase to start synthesizing RNA from the DNA template. Without general transcription factors, RNA polymerase cannot bind to the promoter, and transcription cannot proceed.

What is the TATA box and its significance in transcription?

The TATA box is a DNA sequence found in the promoter region of many eukaryotic genes. It consists of a repeating sequence of adenine (A) and thymine (T) bases. The TATA box is significant because it serves as a binding site for general transcription factors and RNA polymerase, forming the transcription initiation complex (TIC). This complex is essential for the initiation of transcription, as it positions RNA polymerase correctly to start transcribing the gene. Without the TATA box, the assembly of the TIC would be inefficient, hindering gene expression.

What are specific transcription factors and how do they differ from general transcription factors?

Specific transcription factors are proteins that regulate the transcription of particular genes, unlike general transcription factors, which are required for all genes. Specific transcription factors bind to control elements, which can be either distal (enhancers) or proximal to the promoter region. These factors increase or decrease the transcription of specific genes by interacting with the transcription machinery and other regulatory proteins. Their role is crucial for the precise regulation of gene expression, allowing cells to respond to various signals and conditions.

What are enhancers and how do they function in gene regulation?

Enhancers are regions of noncoding DNA that contain distal control elements. They are located far from the promoter region of a gene and serve as binding sites for specific transcription factors. When these transcription factors bind to enhancers, they facilitate the formation of a loop in the DNA, bringing the enhancer in close proximity to the promoter. This interaction enhances the recruitment of the transcription initiation complex (TIC) and RNA polymerase, thereby increasing the transcription of the target gene. Enhancers play a critical role in the precise and efficient regulation of gene expression.

How do proximal control elements influence gene transcription?

Proximal control elements are regions of noncoding DNA located close to the promoter region of a gene. They serve as binding sites for specific transcription factors, which can either activate or repress the transcription of the gene. By binding to these proximal control elements, specific transcription factors can influence the assembly and stability of the transcription initiation complex (TIC) at the promoter. This regulation ensures that the gene is transcribed at the right time and in the right amount, contributing to the precise control of gene expression in eukaryotic cells.