Conjugation: F Plasmids - Online Tutor, Practice Problems & Exam Prep

Conjugation in bacteria involves the transfer of genetic material via conjugative plasmids, specifically the F plasmid, which stands for fertility. F+ cells, containing the entire F plasmid, act as donor cells and form an F pilus to connect with F- recipient cells. During conjugation, a single strand of the F plasmid is transferred, allowing both cells to become F+. This process is crucial for horizontal gene transfer, enhancing genetic diversity and adaptability in bacterial populations.

F Plasmids

In this video, we're going to continue to talk about conjugation by focusing specifically on F plasmids. And so conjugation actually requires the presence of a special type of plasmid called a conjugative plasmid. And so a conjugative plasmid, as its name implies, is going to be a plasmid that's capable of directing its own transfer to a recipient cell via conjugation. Now the best studied example of a conjugative plasmid is actually the F plasmid. And the F in F plasmid actually stands for fertility. And so the F plasmid or the fertility plasmid, again, is the best studied example of a conjugative plasmid, which means that the F plasmid is capable of directing its own transfer to a recipient cell. And the F plasmid or the fertility plasmid was originally discovered in E. coli bacteria. And so this leads us to 2 main types of cells that we have listed below.

F+ cells are going to contain the entire F plasmid. And so these are going to be donor cells. And so they will be able to donate the F plasmid to recipient cells. And so these F+ cells that contain the entire F plasmid and our donor cells, they are going to be able to synthesize what's known as an F pilus. And the F pilus allows the F+ cells to initiate conjugation. And so, the second type of cell that's going to be important to note are the F- cells, and the F- cells are going to be cells that do not contain the entire F plasmid. And so because they do not contain the entire F plasmid, these F- cells are going to be recipient cells. And it's important to note that F- cells, it is possible for them to contain a small portion of the F plasmid. But again, they do not contain the entire F plasmid. And because they do not contain the entire F plasmid, this also means that F- cells do not have an F pilus. And so because they don't have an F pilus, F- cells cannot initiate conjugation. And so they can only serve as recipients in conjugation.

And so if we take a look at our image below, we can get a better understanding of this. And so notice that here in this image we're focusing on the conjugate of the F plasmid. And on the left, we actually have an image that represents this F plasmid. Okay. So this represents the F plasmid. So this is going to be a DNA molecule, a small circular DNA molecule. And what you'll notice is that the F plasmid has a specific region right here, that's called the tra region or the tra region. And this tra region or the tra region contains genes that are required for conjugation including genes that are going to create the F pilus. And you'll also notice that on this F plasmid, there's another region here called the oriT region. And this oriT region is basically the region, is going to serve as the origin of replication during conjugation. And so the F plasmid will be replicated and replication begins at this oriT region. And so this here is the F plasmid. Once again, F+ cells, as you see here in this image, are going to contain the entire F plasmid. As you see right here, this is the F plasmid. And because F+ cells contain the entire F plasmid, F+ cells once again are going to be donor cells and so they're able to donate F Plasmid to a recipient cell. And because these F+ cells have the entire F plasmid, they're also able to form an F pilus. And this F pilus here is going to initiate conjugation. And we'll be able to talk about how it initiates conjugation a little later in our course.

Now over here on the right, we're showing you an F- cell. And the F- cell again does not contain the entire F plasmid. It could either not contain any of it at all or it may only contain a small portion of the F plasmid. But it does not contain the entire F plasmid. So here we're not showing it at all. And because it does not contain the entire F plasmid, it does not have an F pilus. And so F- cells are not able to initiate conjugation, and they're going to serve as the recipient cell. And so the F+ cell will be the donor cell and it will be able to donate the F plasmid to an F- recipient cell. And then the F- recipient cell will be converted to an F+ cell. And so we'll be able to see how that works in more detail later in our course as we continue to move forward. But for now, this here concludes our brief introduction to the F plasmid and we'll be able to get some practice applying these concepts and learn more as we move forward in our course. So I'll see you all in our next video.

During conjugation, the ____ cell transfers its ___________ to the recipient cell.

• A. F+; chromosome
• B. F+; plasmid
• C. F-; chromosome
• D. F-; plasmid
• E. None of the above

What is the purpose of the conjugative plasmid in conjugation?

• A. Causes the bacterial cell to begin binary fission.
• B. Directs the process of conjugation.
• C. Carries the genes required for conjugation.
• D. Carries the genes for the transducing particle.
• E. A and D.
• F. B and C.

Mechanism of F Plasmid Conjugation in E. coli

In this video, we're going to begin our lesson on the mechanism of F plasmid conjugation in E. Coli. And so for the transfer of the F plasmid to occur from an F+ cell to an F- cell, this actually involves a series of steps that we have numbered down below in this image. Notice that this image is focusing on F plasmid conjugation. In the very first step, the donor cell, which is the F+ cell, is going to contain the entire F plasmid allowing it to form an F pilus. The donor F+ cell is able to initiate conjugation with a recipient cell, which is the F- cell. You can see over here we're saying that the F pilus of the F+ donor cell is going to bind to a receptor on the outer membrane of the F- recipient cell. That's exactly what we can see taking place right here where the F pilus of the donor F+ cell is going to bind, as you see here, to the outer membrane of the F- recipient cell.

Then in step number 2, what you're going to see is that the F pilus is going to retract. When the F pilus retracts, it shortens and therefore pulls the cells closer together. You can see here that the F pilus is retracting, represented by this backwards arrow, and the retraction of the pilus brings the two cells closer together, as you see here and here. The F plasmid itself is actually going to be cut at the oriT region of the F plasmid. Here you can see that the oriT region is indicated in red and the plasmid is being nicked or cut right at that oriT region. What can happen at this point in step 3 is that just a single strand of the F plasmid is going to enter the F- cell and then that single strand is going to be used as a template to replicate the F plasmid within the F- cell. Over here in this image is that the single strand of the F plasmid is going to enter into the F- cell, but as it's entering, it's being replicated. You can see that the yellow border here corresponds with the yellow replicate that you see here.

Once the transfer of the entire F plasmid is complete, then what happens is both the donor and the recipient cells are going to be F+ cells because they each have a full copy of the F plasmid. You can see over here we have the donor F+ cell still retains its entire plasmid, and the recipient cell is now F+ because it contains the entire F plasmid that was transferred once again, from the F+ cell over to the F- cell. This is a big takeaway of F plasmid conjugation is that both cells at the end of conjugation are going to be F+. This is going to be different as we talk about other types of conjugation. So this is really important to keep in mind. So this here concludes our brief introduction to the mechanism of F plasmid conjugation in E. Coli. Once again, we'll be able to get some practice applying these concepts and learn about other types of conjugation as we move forward in our course. So I'll see you all in our next video.

What is the process where DNA is transferred from one bacterial cell to another through a pilus?

• A. Horizontal gene transfer by conjugation.
• B. Horizontal gene transfer by transduction.
• C. Horizontal gene transfer by transformation.
• D. Vertical gene transfer by transduction.
• E. Vertical gene transfer by transformation.

Which of the following statements about conjugation is true?

• A. Transferring DNA between cells in conjugation requires a virus carrier.
• B. The donor and recipient cell must be in direct contact (touching) to transfer DNA.
• C. Conjugation can only occur between bacteria of the same species.
• D. Conjugation can occur with or without a conjugative plasmid.

Which of the following statements about conjugation is false?

i. Conjugation is a form of horizontal gene transfer.
ii. Conjugation forms a bridge between two bacterial cells called a plasmid.
iii. Conjugation involves the transfer of genetic information via bacteriophages.

• A. i only.
• B. ii only.
• C. iii only.
• D. i and ii only.
• E. ii and iii only.
• F. i and iii only.

For a bacterium to be able to conjugate it must possess a _____ with genes that encode a _____.

• A. Nucleoid; plasmid.
• B. Plasmid; pilus.
• C. Nucleoid; pilus.
• D. Pilus; plasmid.

Here’s what students ask on this topic:

What is the role of the F plasmid in bacterial conjugation?

The F plasmid, or fertility plasmid, plays a crucial role in bacterial conjugation by enabling the transfer of genetic material between bacteria. F+ cells, which contain the entire F plasmid, act as donor cells. They form an F pilus, a structure that connects to F- recipient cells, which lack the full F plasmid. During conjugation, a single strand of the F plasmid is transferred from the F+ donor to the F- recipient. This process allows both cells to become F+, thereby facilitating horizontal gene transfer. This mechanism enhances genetic diversity and adaptability in bacterial populations.

How does the F pilus function in the conjugation process?

The F pilus is a hair-like appendage formed by F+ cells, which contain the entire F plasmid. Its primary function is to initiate conjugation by connecting the F+ donor cell to an F- recipient cell. The F pilus binds to a receptor on the outer membrane of the F- cell. Once attached, the pilus retracts, pulling the two cells closer together. This proximity allows the transfer of a single strand of the F plasmid from the donor to the recipient. The recipient cell then uses this strand as a template to replicate the entire F plasmid, converting it into an F+ cell.

What are the main differences between F+ and F- cells?

F+ cells contain the entire F plasmid and can act as donor cells in the conjugation process. They are capable of forming an F pilus, which is essential for initiating conjugation. In contrast, F- cells do not contain the entire F plasmid and therefore cannot form an F pilus. As a result, F- cells can only serve as recipient cells during conjugation. After receiving the F plasmid from an F+ donor, the F- cell becomes an F+ cell, gaining the ability to form an F pilus and act as a donor in future conjugation events.

What is the significance of the oriT region in the F plasmid?

The oriT (origin of transfer) region in the F plasmid is crucial for the conjugation process. It serves as the starting point for the transfer of the F plasmid from the donor (F+) cell to the recipient (F-) cell. During conjugation, the F plasmid is nicked at the oriT region, allowing a single strand of the plasmid to be transferred to the recipient cell. This single strand is then used as a template to replicate the entire F plasmid within the recipient cell, converting it into an F+ cell. The oriT region ensures the precise initiation and regulation of plasmid transfer.

How does the transfer of the F plasmid affect the genetic diversity of bacterial populations?

The transfer of the F plasmid through conjugation significantly enhances the genetic diversity of bacterial populations. By enabling the horizontal transfer of genetic material between bacteria, conjugation allows for the spread of beneficial genes, such as those conferring antibiotic resistance or metabolic capabilities. This genetic exchange increases the adaptability and survival of bacterial populations in changing environments. The conversion of F- cells to F+ cells during conjugation also facilitates further genetic exchanges, promoting continuous genetic diversity and evolution within bacterial communities.