Prokaryotic Reproduction - Online Tutor, Practice Problems & Exam Prep

Prokaryotes reproduce asexually through binary fission, resulting in two identical daughter cells. Despite this, genetic variation can occur via mutations due to short generation times and large populations. Additionally, prokaryotes can introduce genetic variation through transformation, where they uptake external DNA, and transduction, where viruses transfer DNA between cells. Conjugation involves direct gene transfer between linked cells using a pilus, often involving F plasmids that can confer traits like antibiotic resistance. These mechanisms highlight the adaptability and evolutionary potential of prokaryotic organisms.

Introduction to Bacterial Plasmids

In this video, we're going to begin our introduction to bacterial plasmids. And so plasmids are really just small molecules of circular double stranded DNA that can be replicated independently of the cell's chromosome. Now these plasmids typically contain genes that are not required for survival of the cell. And so if the cell loses a plasmid, in many cases the cell will still be able to survive. Now that being said, some plasmids do have genes that provide key features for survival.

For example, antibiotic resistance. But for the most part, plasmids do not have genes required for survival. Now the plasmids are going to be replicated by the cell's DNA polymerase, which is the enzyme that performs DNA replication. Now curing is actually a process where the cell loses its plasmid. And when the cell loses its plasmid, this can actually be something that happens spontaneously or naturally, or it's something that can be induced chemically by a scientist.

And so if we take a look at our image down below, we can get a better understanding of plasmid curing with chemical induction. And so notice on the left-hand side over here, we're showing you a bacterial cell. And notice that the bacterial cell has its own chromosomal DNA here in red. But notice that over here in green, there's a circular, small circular double stranded DNA molecule that we call a plasmid. And once again, this plasmid does not typically contain genes that are required for survival.

And so through plasmid curing, which can be induced chemically, chemical induction will allow the cell to lose its plasmid. And so you can see that the plasmid is being lost here. It's being removed. And so over here, we have the cell, which no longer has that plasmid. And notice the cell is saying, "that's okay."

I don't really need it. And so once again, in most cases, these plasmids do not have genes that are required for survival. However, in some scenarios, they can have genes that provide key features such as antibiotic resistance. But for now, this here concludes our brief introduction to bacterial plasmids and we'll be able to apply these concepts here as we move forward. So I'll see you all in our next video.

Which of these is NOT true regarding bacterial plasmids?

• A. Bacterial plasmids are found in all bacteria.
• B. Bacterial plasmids are not essential for bacterial life.
• C. Bacterial plasmids replicate independently of the bacterial chromosome.
• D. Bacteria can lose their plasmids in a process called 'plasmid curing'.
• E. Bacterial plasmids are replicated by the same DNA machinery that replicated the bacterial chromosome.

Which types of genes are commonly found in bacterial plasmids?

• A. Genes that encode for proteins used in cellular respiration.
• B. Genes that encode for proteins used in DNA replication.
• C. Genes that encode for antibiotic resistance.
• D. Genes that encode for cell envelope/membrane development.

Binary Fission

In this video, we're going to begin our lesson on binary fission. Recall from our previous lesson videos that prokaryotic organisms replicate by the process of binary fission. However, eukaryotes do not divide by binary fission; they divide by mitosis. Now, binary fission can be defined as prokaryotic asexual reproduction.

Meaning that there's only one single parental cell that will divide to form 2 new daughter cells. The term "daughter cells" refers to either of the 2 final cells that form after a cell divides. If we take a look at our image below, notice on the left-hand side, we're showing you our parental prokaryotic cell. Notice that its chromosome, which is here in blue, is not within a nucleus. It is a circular chromosome, and so this is a prokaryotic cell.

This single parental prokaryotic cell, when it's ready to divide, will divide by the process of binary fission. The process of binary fission allows this single parental cell to divide into 2 daughter cells. We can label these as the daughter cells. Once again, the daughter cells are the final cells that result from binary fission. This process of binary fission actually contains a few steps, critical steps that include replicating the chromosome so that each of the daughter cells is able to get a copy of the chromosome.

But for now, this concludes our brief introduction to binary fission, and I'll see you guys in our next video.

The cellular process by which two bacterial daughter cells arise from one bacterial parent cell is known as:

• A. Conjugation
• B. Meiosis
• C. Binary fission
• D. Mitosis

Horizontal Gene Transfer

In this video, we're going to begin our lesson on horizontal gene transfer. Recall from our previous lesson videos that horizontal gene transfer occurs between two organisms that are not direct descendants of one another. These two organisms are going to be transferring genes between each other. Horizontal gene transfer allows cells to quickly acquire new traits and it also drives genetic diversity among organisms. Now there are three known mechanisms of horizontal gene transfer in bacteria.

Notice that we have those three mechanisms numbered down below: 1, 2, and 3. The first mechanism is transformation. The second mechanism is transduction. The third mechanism of horizontal gene transfer is conjugation. What you'll notice is that these numbers correspond with the numbers in our image.

For the first mechanism of horizontal gene transfer, we have transformation. Transformation is horizontal gene transfer via the uptake of free or naked DNA in the environment by a cell. If we take a look at our image down below at number 1 on the left-hand side, notice it's showing you transformation. Transformation occurs when a cell brings in free or naked DNA from the environment. When the free or naked DNA is brought into the cell and incorporated into the cell, we refer to this as transformation.

Later in our course, we'll be able to talk more about transformation. Transduction is, again, going to be a form of horizontal gene transfer. It occurs between cells and is mediated specifically by a bacteriophage virus. A bacteriophage is a specific type of virus that infects bacteria. If we take a look at number 2 down below, notice that this is showing us transduction, which is not to be confused with transformation because they sound similar, but they are different.

It is showing you a bacteriophage or just a phage for short. The bacteriophage is responsible for transferring DNA into the cell. You can see that donor cell DNA is being transferred by the bacteriophage, and the recipient can receive that DNA. Again, we'll get to talk more about transduction later in our course. This is just the introduction to it.

The third and final mechanism of horizontal gene transfer is conjugation. This refers to the direct horizontal DNA transfer between cells during direct cell-to-cell contact. Notice that the final image over here is focusing on conjugation. We have two neighboring cells and they end up forming direct cell-to-cell contact where DNA and genes can be transferred from one organism over to a neighboring organism. Notice that the green molecule originally was not in this cell on the right, but now at the end, both cells have the green molecule.

This is an example of conjugation, the transfer of genes via direct cell-to-cell contact. Again we'll be able to talk more about conjugation later in our course. This is just the introduction. You can see that this is really our map of our lesson on horizontal gene transfer and moving forward we'll get to talk more about each of these mechanisms in more detail. Starting with transformation, then we'll move on to transduction, and last but not least, we'll move on to conjugation.

This concludes our brief intro to horizontal gene transfer, and I'll see you all in our next video.

Which of the following is not a type of horizontal gene transfer?

• A. Transduction.
• B. Transformation.
• C. Transamination.
• D. Conjugation.

Bacterial Transformation

This video, we're going to begin our lesson on bacterial transformation, a type of horizontal gene transfer. And so recall from our previous lesson videos once again that transformation is a type of horizontal gene transfer that's characterized by the uptake of free or naked DNA in the environment by the cell. And so the cell is able to uptake free or naked DNA from the environment, and that is called transformation. Now, in order for a cell to transform DNA, it must be known as a competent cell. And a competent cell is really describing a really complex physiological state.

And so, competent cells are really cells that have the ability to transform DNA from the environment, in other words, uptake naked DNA from the environment. If a cell is not competent, then it will not be able to transform DNA. And so if we take a look at our image down below, notice that it's distinguishing competent cells versus non-competent cells. And so notice the cell that's over here on the left is a totally competent cell. And again, competency is describing a really complex physiological state, but in the end, competent cells have the ability to transform or uptake DNA from the environment.

And so notice that this cell is able to transform naked DNA from the environment. And so this naked DNA is just this bare DNA that you see here, and it's able to transform it or uptake that naked DNA. So you can see the naked DNA is able to make its way into the cell because the cell is competent. However, a cell that is not competent, like this one over here, notice is not able to uptake DNA. It's not able to transform DNA, and so the DNA is not able to get into the cell if it's not competent.

And so only competent cells are capable of transformation. Now, cells can actually be either naturally competent or cells can be induced to be competent by chemical treatment. And so some chemical treatments can induce cells to become more competent and allow them to transform or uptake external DNA. And so this here concludes our brief lesson or our brief intro to bacterial transformation and competent cells, and we'll be able to learn more about transformation as we continue to move forward in our course. So I'll see you all in our next video.

What does it mean when a bacterial cell is naturally competent?

• A. The bacterial cell is able to transform its chromosomal DNA into RNA.
• B. The bacterial cell is able to transform DNA from their environment.
• C. The bacterial cell is able to degrade viral DNA from attacking viruses.
• D. The bacterial cell is able to take in naked DNA and incorporate that DNA into its genome.
• E. A and C.
• F. B and D.

Bacterial cells can become competent in two ways, which are:

• A. Spontaneously.
• B. Instinctively.
• C. Horizontally.
• D. Induced.
• E. A and D.
• F. A and C.
• G. B and C.

Transduction

In this video, we're going to begin our lesson on transduction. Recall from our previous lesson videos that transduction is another type of horizontal gene transfer or horizontal DNA transfer that occurs between cells and is mediated by what are known as bacteriophage viruses, otherwise just known as phages. Bacteriophages or just phages are viruses that infect bacteria. To be a little more formal, phages can be defined as bacterial obligate intracellular parasites, which means that they have to infect living bacteria and use the cell machinery of the living bacteria to replicate. These phages are made of either DNA or RNA packed into a protein coat.

These phages infect living cells, then they use the cellular machinery of those living cells to replicate, and then they ultimately end up lysing the cell or causing the cell to rupture. When the cell ruptures, it releases new phage particles, and those phage particles can be released and then initiate another infection of a different cell. Transduction involves horizontal DNA transfer using these bacteriophage viruses. It actually results from an error consisting of bacterial DNA accidentally being packaged into the phage instead of viral DNA being packaged.

When this error occurs and bacterial DNA is packaged into the phage, this creates what is called a transducing particle. A transducing particle is a defective phage that is carrying bacterial DNA instead of carrying its own viral DNA. This bacterial DNA can then be horizontally transferred to another organism. Let's take a look at this image below to get a better understanding of the production of these transducing particles. We have our cell here in this circle. Inside the cell, we have the bacterial DNA, the bacterial chromosome. The red structure you see here represents the bacteriophage. The bacteriophage, or just the phage, will attach and inject viral DNA into the bacterial cell.

Phage enzymes, which are also going to be injected, are going to cut the bacterial DNA. Notice that the bacterial DNA is being cut into a whole bunch of different pieces. Then, the bacteriophage DNA will replicate, and you can see that from one molecule of the phage DNA in green, we now have multiple molecules. In addition to the phage DNA replicating, viral proteins are also going to be made. More viral proteins represented by these red shells here will be formed. The transducing particle comes into play due to an error where bacterial DNA is accidentally packaged into the phage instead of viral DNA. Some bacteriophages are going to contain phage DNA in green, representing another virus that could conduct another viral infection. But sometimes, there is an error where the phage is packaged with bacterial DNA, shown by these little blue particles, which are phages containing bacterial DNA. These phages are referred to as transducing particles.

The transducing particle is a virus, a phage, that contains bacterial DNA. When this transducing particle goes to initiate another infection for a different cell, it will be injecting bacterial DNA instead of injecting phage DNA. This is how genes can be transferred between different bacteria using bacteriophages. This process is called transduction. This concludes our brief introduction to transduction and transducing particles.

As we move forward in our course, we will be able to continue to talk more about transduction. I'll see you all in our next video.

Transduction is a form of horizontal gene transfer which requires a carrier for the genetic information being transferred. What is this carrier and what is it made of?

• A. Transduction particle made of a human virus carrying bacterial DNA.
• B. Transformation particle made of bacteriophage carrying human DNA.
• C. Transduction particle made of a bacteriophage carrying bacterial DNA.
• D. Transduction particle made of a bacteriophage carrying viral DNA.

Introduction to Conjugation

In this video, we're going to begin our introduction to conjugation. And so first recall from our previous lesson videos that conjugation is one of the 3 main types of horizontal gene transfer. Conjugation is really just the direct transfer of DNA between 2 bacterial cells that are making direct cell-to-cell contact. Conjugation is going to require both a donor cell that will be donating the DNA and a recipient cell that will be receiving the DNA from the donor cell. Conjugation can either transfer a plasmid or it could transfer part of the donor cell's chromosomal DNA.

Now, there are 3 main types of conjugation that we have numbered down below: 1, 2, and 3. The first main type of conjugation is going to be F+ plasmid conjugation. The second main type of conjugation is going to be HFR cell conjugation. The third main type of conjugation is going to be F' plasmid conjugation where this little apostrophe here is stated as 'prime'. So, this is F' conjugation.

As we move forward in our course, we're going to talk about each of these three main types of conjugation in more detail in their own separate videos. But for now, notice that we're showing you an image or a map of our lesson on these three main types of conjugation. On the far left, once again, we have F+ plasmid conjugation, in the middle, we have HFR cell conjugation, and on the far right, we have F' cell conjugation. Within here, we give you some details of each of these different types of conjugation.

But once again, we're gonna talk more about each of these different types of conjugation as we move forward in their own separate videos. So, you don't really need to worry too much about the details that you see here right now. You can always come back and review this image after we've covered those more in-depth videos. What you'll notice about F+ plasmid conjugation, one of the main features that we're going to emphasize as we move forward as well, is that the entire F plasmid is going to be transferred from the donor cell to the recipient cell. With HFR cell conjugation, what we'll see is that only some or only part of the integrated F plasmid is going to be transferred, along with some of the donor cell's chromosomal DNA.

And once again, we'll be able to talk more about HFR cell conjugation later in our course. And then, last but not least, over here on the far right, what we have is F' cell conjugation. In this one, what we see is that, once again, the entire F' plasmid, with integrated donor DNA is going to be transferred. And once again, we'll be able to talk more about F' cell conjugation later in our course in a different video.

But for now, this here concludes our brief introduction to conjugation and the 3 main types of conjugation, and we'll get to learn more about these 3 main types of conjugation as we move forward in our course. So I'll see you all in our next video.

How is conjugation different from the two other forms of horizontal gene transfer, transformation and transduction?

• A. Conjugation directly transfers DNA from donor to recipient cell.
• B. Conjugation requires a phage to transfer the DNA between cells.
• C. Conjugation requires a donor and a recipient cell.
• D. Conjugation allows the recipient cell to take in free DNA from the environment.
• E. A and D.
• F. B and C.

Sex Pilus

In this video, we're going to introduce the sex pilus. And so the sex pilus is also referred to as the conjugation pilus. And what it does is it connects two cells directly for a special type of DNA transfer known as conjugation. And so conjugation can be defined as the process by which DNA is transferred, or the process of transferring DNA directly from one bacterial cell to another bacterial cell by using direct contact through the sex pilus or the conjugation pilus. Now this transferred DNA that occurs via conjugation can actually add a new function to a cell.

For example, resistance to antibiotics. And so if we take a look at this image down below, we can get a better understanding of how a sex pilus can bring two cells together to directly transfer genetic material from one cell to another cell. And so notice over here in this part of the image that we're showing you two bacterial cells. Bacterial cell A is over here, and bacterial cell B is over here. And notice that bacterial cell A has this little yellow circle here, which is representing a DNA plasmid.

And it has, some, perhaps antibiotic resistance on this plasmid. And so bacterial cell A has the plasmid and is resistant to antibiotics. But notice that cell B over here does not have that little yellow circle. And so it is going to, not be resistant to antibiotics. It will be sensitive to antibiotics.

However, through this green structure that you see here, which is the sex pilus itself or the conjugation pilus, what can happen is that the sex pilus can, help to bring the two cells into closer proximity, move the two cells together. So notice that the movement of the cells is towards each other, because of the actions of the sex pilus. And so, the sex pilus can help with this process of conjugation to transfer this DNA plasmid over to the other cell. And so that's what we see over here in this image is, the DNA is actually being copied and transferred over, to cell B. And so you can see here that the DNA plasmid is being replicated and being copied and transferred over to cell B.

And in the end over here, notice that we have cell A and cell B both have that plasmid. So that DNA has been transferred from cell A over to cell B, through the action of the sex pilus. And notice that both cell A and cell B each have their own sex pilus, and so now cell B can move on to transfer its DNA to another cell that may not have it. And so this is through the action of the sex pilus or conjugation pilus. And this concludes our lesson here, so I'll see you all in our next video.

Which of the following is NOT a function of pili?

• A. Gliding motility of cells
• B. Conjugation (DNA transfer)
• C. Antibiotic resistance
• D. Twitching motility of cells
• E. All are functions of pili

F Plasmids

In this video, we're going to continue to talk about conjugation by focusing specifically on F plasmids. Conjugation actually requires the presence of a special type of plasmid called a conjugative plasmid. 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. The best studied example of a conjugative plasmid is the F plasmid. The 'F' in F plasmid actually stands for fertility.

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. The F plasmid, or the fertility plasmid, was originally discovered in E. coli bacteria. This leads us to two main types of cells that we have listed down below. F⁺ cells are going to contain the entire F plasmid.

These are going to be donor cells, and they will be able to donate the F plasmid to recipient cells. These F⁺ cells that contain the entire F plasmid and are donor cells, they are going to be able to synthesize what's known as an F pilus. The F pilus allows the F⁺ cells to initiate conjugation. The second type of cell that's going to be important to note are the F^- cells, and F^- cells are going to be cells that do not contain the entire F plasmid.

Because they do not contain the entire F plasmid, these F^- cells are going to be recipient cells. 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. Because they don't have an F pilus, F^- cells cannot initiate conjugation.

They can only serve as recipients in conjugation. If we take a look at our image down below, we can get a better understanding of this. Notice that here in this image we're focusing on the conjugate of F plasmid, and on the left we actually have an image that represents this F plasmid. This represents the F plasmid.

It is going to be a DNA molecule, a small circular DNA molecule. What you'll notice is that the F plasmid has a specific region right here, that's called the tra region or the tri region. The tra region or the tri region contains genes that are required for conjugation including genes that are going to create the F pilus. You'll also notice that on this F plasmid there's another region here called the origin of transfer or oriT region. The oriT region is basically the region that is going to serve as the origin of replication during conjugation.

The F plasmid will be replicated and replication begins at this oriT region. Once again, F⁺ cells, as you see here in this image, are going to contain the entire F plasmid. Because F⁺ cells contain the entire F plasmid, they are going to be donor cells and so they're able to donate the F plasmid to a recipient cell.

Because these F⁺ cells have the entire F plasmid, they're also able to form an F pilus. This F pilus here is going to initiate conjugation. We'll be able to talk about how it initiates conjugation a little later in our course. Now, on the right we're showing you an F^- cell. 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.

The F, what we're going to learn is that the F⁺ cell will be the donor cell and it will be able to donate the F plasmid to an F^- recipient cell. Then, the F^- recipient cell will be converted to an F⁺ cell. 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. 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. 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, contains 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.

What you can see over here is 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, where the F pilus of the donor F+ cell binds, as you see here, to the outer membrane of the F- recipient cell. Then in step number 2, you're going to see that the F pilus retracts. 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 backward arrow, and the retraction of the pilus brings the two cells closer together, as you see here and here.

Then, 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. That single strand is going to be used as a template to replicate the F plasmid within the F- cell. You can see over here in this image that the single strand of the F plasmid is going to enter into the F- cell, and 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. It is being replicated as it enters into the F- cell. Once the transfer of the entire F plasmid is complete, then what happens is both the donor and the recipient cell are going to be F+ cells because they each have a full copy of the F plasmid. You can see over here that 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, 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. This is really important to keep in mind. 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.

Hfr Cell Conjugation

In this video, we're going to begin our lesson on the conjugation of HFR cells, as well as the conjugation of f prime cells. However, in this video, we're only going to focus on the conjugation of HFR cells. And then later in a different video, we'll focus on the conjugation of f prime cells. And so in order to understand HFR cell conjugation, it's first important to highlight an important fact. And that is that f plasmids have the reversible ability to integrate itself into the host chromosome, and it can also excise or remove itself from the host chromosome.

An HFR cell, where the HFR really stands for high frequency of recombination, these HFR or high frequency of recombination cells are simply cells that have an f plasmid integrated into the host chromosome. And so if we take a look at our image down below, specifically on the left-hand side over here, notice that this box is focused on the reversible HFR cell formation. And so notice that the top cell that you see here is actually the same F plus cell that we talked about in our previous lesson videos because it's a cell that contains the entire F plasmid and therefore it forms this pilus that you see over here. Now again, this f plasmid has the ability, reversible ability, to integrate itself into the chromosome. And so that means that this plasmid has the ability to integrate here into the DNA of the host.

And so when it does integrate, represented by this blue arrow down below, that is what forms the HFR cell. And so the HFR cell is a cell that has an integrated f plasmid into the chromosome as you see here in this image. Now again, the integration of this f plasmid is reversible, which means that the F plasmid can excise itself or remove itself to become the F plasmid again. And so that's what we see here with the excises arrow pointing back upwards, shows you that the F plasmid once again can come back out, and become an F plus cell. And so, what we can see here is that F plus cells and HFR cells can be converted into each other depending on the integration status of the F plasmid.

If the F plasmid is integrated, it's an HFR cell, whereas if the F plasmid is not integrated, it's an F plus cell. Now in our last lesson video, we were able to talk about the conjugation of these F plus cells. And so in this video, we're going to be focusing on the conjugation of these HFR cells. And so during the conjugation of the HFR cells, these HFR cells are going to serve as the donor cells and the transfer of chromosomal DNA to the recipient cell via conjugation. And so instead of only transferring the F plasmid, in an HFR cell conjugation, part of the donor cell's chromosomal DNA is going to be transferred, and that is a big difference from what we saw in our previous videos.

Now what we'll see is that there are also some similarities between the conjugation of HFR cells' chromosomal DNA and the conjugation of the F plasmid and E. Coli. There are some similarities between the two. However, there are also some key differences. And so, some of those key differences include the fact that HFR cells, they are going to be making the f pilus to conjugate with the f minus cell. However, the entire integrated f plasmid is not going to be transferred to the recipient, which means that at the end of conjugation the recipient is still going to remain f minus and so the recipient stays f minus from the beginning to the end of the conjugation process. And so this is very different than what we've seen in our previous videos where both cells were, F plus at the end of conjugation. However, here with HFR cell conjugation, the recipient stays f minus. And this is again because the recipient does not receive the entire f plasmid. Now, again, we can emphasize that only a really, really small portion, only small portions of the donor cell's, chromosomal DNA as well as a small portion of the f plasmid are going to be transferred to the recipient.

And so, that transferred DNA that the f minus recipient cell receives is either going to integrate into the recipient cell's host chromosome or it will be degraded and have no effect. And so if we take a look at our image down below, we can get a better understanding of HFR cell conjugation. Now over here

Hfr strains of bacteria:

• A. Do not have an F plasmid.
• B. Have an F plasmid.
• C. Have an F factor integrated in the bacterial chromosome.
• D. Have a partial F plasmid as a linear fragment in the cytoplasm.

What is transferred between two bacterial cells in Hfr conjugation?

• A. A small portion of the integrated F plasmid from the Hfr donor cell.
• B. A small, random portion of the Hfr donor's cells chromosome.
• C. A small portion of the Hfr donor cell's chromosome and integrated F plasmid.

Plasmids

This video, we're going to focus on plasmids. Plasmids can be defined as circular double-stranded DNA molecules with an origin of replication allowing them to replicate within a cell. Some plasmids are known as high copy number plasmids, and these are plasmids that will replicate very fast or very quickly inside a cell. Other plasmids are known as low copy number plasmids and so they replicate very, very slowly within the cell. These high copy number plasmids that replicate quickly, of course, are going to be found in high numbers or high copy numbers because they replicate so fast.

Whereas, the low copy number plasmids that replicate slowly are going to be found in relatively low numbers within the cell or low copy number. These plasmids, regardless of if they are high copy number or low copy number plasmids, can carry various genes. Sometimes some of those genes are going to be able to provide the cell with the ability to survive in a particular environment, such as an environment that contains antibiotics, for example. We call these plasmids resistance plasmids, otherwise known as r plasmids. Resistance plasmids or r plasmids are plasmids that encode genes that confer resistance to antibiotics, allowing the cell to survive in the presence of antibiotics.

These genes, that are found on the resistance plasmids, are sometimes referred to as r genes. In addition to the r genes, it's important to note that these plasmids can also have other genes. Most of the resistance plasmids are going to be conjugative plasmids, which means that these plasmids can be horizontally transferred between different species via conjugation. Other than the r genes, they can also contain other genes that are required for DNA transfer by conjugation. If we take a look at our image down below over here on the left-hand side, notice that the top half of this image is focusing on high copy number plasmids.

High copy number plasmids replicate very quickly within the cell, and so they're going to be found in relatively high numbers, high copy numbers within the cell. Whereas the low copy number plasmids on the bottom half over here, you’ll notice they replicate very slowly over time, and so they're going to be found in relatively low numbers within the cell. Here is a representation of a plasmid and some of the different regions of DNA that can be found within the plasmid. This is specifically an r plasmid here, a resistance plasmid. It’s a resistance plasmid because it contains specific genes that allow for antibiotic resistance, such as an amp^r gene, which allows for ampicillin resistance, a gene that allows for ampicillin resistance, allowing the cell to survive in the presence of ampicillin.

At the top is a region, a gene, the tetr gene or tetracycline resistance, resistance to another antibiotic. Then in purple what we have is a can^r gene providing resistance to an antibiotic called kanamycin. In addition to being an r plasmid, it's also a conjugated plasmid as well because it contains this tra region or tra region here, which is the region that is important for conjugation, allowing the r plasmid to be horizontally transferred and passed from cell to cell via conjugation. This also allows for the spreading of resistance genes between different species of bacteria. This concludes our brief lesson on plasmids and how they contribute to genome variability because they are mobile genetic elements that can be passed from one cell to another cell via conjugation.

We'll be able to talk about other mobile genetic elements as we move forward in our course. So, I'll see you all in our next video.

Here’s what students ask on this topic:

How do prokaryotes reproduce asexually?

Prokaryotes reproduce asexually through a process called binary fission. In binary fission, a single bacterial cell replicates its genetic material and then divides into two identical daughter cells. This process allows for rapid population growth, especially under optimal conditions with sufficient nutrients. The steps include DNA replication, elongation of the cell, and division into two cells. Each daughter cell receives an identical copy of the parent cell's chromosome and any plasmids present. Despite the lack of genetic variation through binary fission, mutations can occur, contributing to genetic diversity over time.

What is the role of mutations in prokaryotic genetic variation?

Mutations play a significant role in prokaryotic genetic variation. Although binary fission produces genetically identical daughter cells, the high frequency of mutations during DNA replication introduces genetic diversity. This is particularly impactful due to the short generation times and large populations of prokaryotes. Even small mutations can accumulate rapidly, leading to evolutionary changes. These mutations can result in new traits, such as antibiotic resistance, which can be advantageous for survival in changing environments.

How does transformation contribute to genetic variation in prokaryotes?

Transformation is a process where prokaryotes incorporate external DNA from their environment into their own genome. This exogenous DNA can come from dead cells or other sources. When a prokaryotic cell takes up this DNA, it can integrate it into its chromosome or plasmids, leading to genetic variation. Transformation can occur between different species, allowing for the transfer of beneficial genes, such as those conferring antibiotic resistance. This process enhances genetic diversity and adaptability in prokaryotic populations.

What is transduction in prokaryotes?

Transduction is a method of genetic exchange in prokaryotes mediated by viruses, specifically bacteriophages. During this process, a bacteriophage infects a bacterial cell and incorporates bacterial DNA into its viral particles. When the bacteriophage infects another bacterial cell, it transfers this bacterial DNA along with its own viral DNA. The recipient cell can then integrate the transferred bacterial DNA into its genome, resulting in genetic variation. Transduction can occur within the same species or between different species, facilitating the spread of genetic traits.

How does conjugation differ from other methods of genetic exchange in prokaryotes?

Conjugation is a direct method of genetic exchange between two physically connected prokaryotic cells. It involves the transfer of genetic material through a pilus, a specialized appendage. The donor cell, which contains the F plasmid (or F factor), extends the pilus to connect with the recipient cell. The genetic material, including the F plasmid, is then transferred to the recipient cell. Unlike transformation and transduction, conjugation requires direct cell-to-cell contact. This process can transfer genes that confer advantageous traits, such as antibiotic resistance, enhancing genetic diversity and adaptability.